On partial uninit error point at where we need init

When a binding is declared without a value, borrowck verifies that all
codepaths have *one* assignment to them to initialize them fully. If
there are any cases where a condition can be met that leaves the binding
uninitialized or we attempt to initialize a field of an unitialized
binding, we emit E0381.

We now look at all the statements that initialize the binding, and use
them to explore branching code paths that *don't* and point at them. If
we find *no* potential places where an assignment to the binding might
be missing, we display the spans of all the existing initializers to
provide some context.

compiler/rustc_borrowck/src/borrowck_errors.rs

@@ -33,22 +33,6 @@ impl<'cx, 'tcx> crate::MirBorrowckCtxt<'cx, 'tcx> {
         err
     }
 
-    pub(crate) fn cannot_act_on_uninitialized_variable(
-        &self,
-        span: Span,
-        verb: &str,
-        desc: &str,
-    ) -> DiagnosticBuilder<'cx, ErrorGuaranteed> {
-        struct_span_err!(
-            self,
-            span,
-            E0381,
-            "{} of possibly-uninitialized variable: `{}`",
-            verb,
-            desc,
-        )
-    }
-
     pub(crate) fn cannot_mutably_borrow_multiply(
         &self,
         new_loan_span: Span,
@@ -175,8 +159,7 @@ impl<'cx, 'tcx> crate::MirBorrowckCtxt<'cx, 'tcx> {
             self,
             new_loan_span,
             E0501,
-            "cannot borrow {}{} as {} because previous closure \
+            "cannot borrow {}{} as {} because previous closure requires unique access",
-             requires unique access",
             desc_new,
             opt_via,
             kind_new,
@@ -453,9 +436,8 @@ impl<'cx, 'tcx> crate::MirBorrowckCtxt<'cx, 'tcx> {
             self,
             closure_span,
             E0373,
-            "{} may outlive the current function, \
+            "{} may outlive the current function, but it borrows {}, which is owned by the current \
-             but it borrows {}, \
+             function",
-             which is owned by the current function",
             closure_kind,
             borrowed_path,
         );
@@ -479,7 +461,7 @@ impl<'cx, 'tcx> crate::MirBorrowckCtxt<'cx, 'tcx> {
     }
 
     #[rustc_lint_diagnostics]
-    fn struct_span_err_with_code<S: Into<MultiSpan>>(
+    pub(crate) fn struct_span_err_with_code<S: Into<MultiSpan>>(
         &self,
         sp: S,
         msg: impl Into<DiagnosticMessage>,

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -2,9 +2,12 @@ use either::Either;
 use rustc_const_eval::util::CallKind;
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxHashSet;
-use rustc_errors::{Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, MultiSpan};
+use rustc_errors::{
+    struct_span_err, Applicability, Diagnostic, DiagnosticBuilder, ErrorGuaranteed, MultiSpan,
+};
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
+use rustc_hir::intravisit::{walk_expr, Visitor};
 use rustc_hir::{AsyncGeneratorKind, GeneratorKind};
 use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::traits::ObligationCause;
@@ -94,32 +97,14 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
                 return;
             }
 
-            let item_msg =
+            let err =
-                match self.describe_place_with_options(used_place, IncludingDowncast(true)) {
+                self.report_use_of_uninitialized(mpi, used_place, desired_action, span, use_spans);
-                    Some(name) => format!("`{}`", name),
-                    None => "value".to_owned(),
-                };
-            let mut err = self.cannot_act_on_uninitialized_variable(
-                span,
-                desired_action.as_noun(),
-                &self
-                    .describe_place_with_options(moved_place, IncludingDowncast(true))
-                    .unwrap_or_else(|| "_".to_owned()),
-            );
-            err.span_label(span, format!("use of possibly-uninitialized {}", item_msg));
-
-            use_spans.var_span_label_path_only(
-                &mut err,
-                format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
-            );
-
             self.buffer_error(err);
         } else {
             if let Some((reported_place, _)) = self.has_move_error(&move_out_indices) {
                 if self.prefixes(*reported_place, PrefixSet::All).any(|p| p == used_place) {
                     debug!(
-                        "report_use_of_moved_or_uninitialized place: error suppressed \
+                        "report_use_of_moved_or_uninitialized place: error suppressed mois={:?}",
-                         mois={:?}",
                         move_out_indices
                     );
                     return;
@@ -326,6 +311,99 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         }
     }
 
+    fn report_use_of_uninitialized(
+        &self,
+        mpi: MovePathIndex,
+        used_place: PlaceRef<'tcx>,
+        desired_action: InitializationRequiringAction,
+        span: Span,
+        use_spans: UseSpans<'tcx>,
+    ) -> DiagnosticBuilder<'cx, ErrorGuaranteed> {
+        // We need all statements in the body where the binding was assigned to to later find all
+        // the branching code paths where the binding *wasn't* assigned to.
+        let inits = &self.move_data.init_path_map[mpi];
+        let move_path = &self.move_data.move_paths[mpi];
+        let decl_span = self.body.local_decls[move_path.place.local].source_info.span;
+        let mut spans = vec![];
+        for init_idx in inits {
+            let init = &self.move_data.inits[*init_idx];
+            let span = init.span(&self.body);
+            spans.push(span);
+        }
+
+        let (item_msg, name, desc) =
+            match self.describe_place_with_options(used_place, IncludingDowncast(true)) {
+                Some(name) => (format!("`{name}`"), format!("`{name}`"), format!("`{name}` ")),
+                None => ("value".to_string(), "the variable".to_string(), String::new()),
+            };
+        let initialized = if let InitializationRequiringAction::PartialAssignment = desired_action {
+            // The same error is emitted for bindings that are *sometimes* initialized and the ones
+            // that are *partially* initialized by assigning to a field of an uninitialized
+            // binding. We differentiate between them for more accurate wording here.
+            "fully initialized"
+        } else if spans.iter().filter(|i| !i.contains(span)).count() == 0 {
+            // We filter above to avoid misleading wording in cases like:
+            // ```
+            // let x;
+            // x += 1;
+            // ```
+            "initialized"
+        } else {
+            "initialized in all conditions"
+        };
+        let mut err = struct_span_err!(self, span, E0381, "binding {desc}isn't {initialized}");
+        use_spans.var_span_label_path_only(
+            &mut err,
+            format!("{} occurs due to use{}", desired_action.as_noun(), use_spans.describe()),
+        );
+
+        if let InitializationRequiringAction::PartialAssignment = desired_action {
+            err.help(
+                "partial initialization isn't supported, fully initialize the binding with \
+                a default value and mutate, or use `std::mem::MaybeUninit`",
+            );
+        }
+        let verb = desired_action.as_verb_in_past_tense();
+        err.span_label(span, format!("{item_msg} {verb} here but it isn't {initialized}",));
+
+        // We use the statements were the binding was initialized, and inspect the HIR to look
+        // for the branching codepaths that aren't covered, to point at them.
+        let hir_id = self.mir_hir_id();
+        let map = self.infcx.tcx.hir();
+        let body_id = map.body_owned_by(hir_id);
+        let body = map.body(body_id);
+
+        let mut visitor = ConditionVisitor { spans: &spans, name: &name, errors: vec![] };
+        visitor.visit_body(&body);
+        if visitor.errors.is_empty() {
+            for sp in &spans {
+                if *sp < span && !sp.overlaps(span) {
+                    err.span_label(*sp, "binding initialized here in some conditions");
+                }
+            }
+        }
+        for (sp, label) in visitor.errors {
+            if sp < span && !sp.overlaps(span) {
+                // When we have a case like `match-cfg-fake-edges.rs`, we don't want to mention
+                // match arms coming after the primary span because they aren't relevant:
+                // ```
+                // let x;
+                // match y {
+                //     _ if { x = 2; true } => {}
+                //     _ if {
+                //         x; //~ ERROR
+                //         false
+                //     } => {}
+                //     _ => {} // We don't want to point to this.
+                // };
+                // ```
+                err.span_label(sp, &label);
+            }
+        }
+        err.span_label(decl_span, "variable declared here");
+        err
+    }
+
     fn suggest_borrow_fn_like(
         &self,
         err: &mut DiagnosticBuilder<'tcx, ErrorGuaranteed>,
@@ -2448,3 +2526,103 @@ impl<'tcx> AnnotatedBorrowFnSignature<'tcx> {
         }
     }
 }
+
+/// Detect whether one of the provided spans is a statement nested within the top-most visited expr
+struct ReferencedStatementsVisitor<'a>(&'a [Span], bool);
+
+impl<'a, 'v> Visitor<'v> for ReferencedStatementsVisitor<'a> {
+    fn visit_stmt(&mut self, s: &'v hir::Stmt<'v>) {
+        match s.kind {
+            hir::StmtKind::Semi(expr) if self.0.contains(&expr.span) => {
+                self.1 = true;
+            }
+            _ => {}
+        }
+    }
+}
+
+/// Given a set of spans representing statements initializing the relevant binding, visit all the
+/// function expressions looking for branching code paths that *do not* initialize the binding.
+struct ConditionVisitor<'b> {
+    spans: &'b [Span],
+    name: &'b str,
+    errors: Vec<(Span, String)>,
+}
+
+impl<'b, 'v> Visitor<'v> for ConditionVisitor<'b> {
+    fn visit_expr(&mut self, ex: &'v hir::Expr<'v>) {
+        match ex.kind {
+            hir::ExprKind::If(cond, body, None) => {
+                // `if` expressions with no `else` that initialize the binding might be missing an
+                // `else` arm.
+                let mut v = ReferencedStatementsVisitor(self.spans, false);
+                v.visit_expr(body);
+                if v.1 {
+                    self.errors.push((
+                        cond.span,
+                        format!(
+                            "this `if` expression might be missing an `else` arm where {} is \
+                             initialized",
+                            self.name,
+                        ),
+                    ));
+                }
+            }
+            hir::ExprKind::If(cond, body, Some(other)) => {
+                // `if` expressions where the binding is only initialized in one of the two arms
+                // might be missing a binding initialization.
+                let mut a = ReferencedStatementsVisitor(self.spans, false);
+                a.visit_expr(body);
+                let mut b = ReferencedStatementsVisitor(self.spans, false);
+                b.visit_expr(other);
+                match (a.1, b.1) {
+                    (true, true) | (false, false) => {}
+                    (true, false) => {
+                        self.errors.push((
+                            cond.span,
+                            format!("{} is uninitialized if this condition isn't met", self.name,),
+                        ));
+                    }
+                    (false, true) => {
+                        self.errors.push((
+                            cond.span,
+                            format!("{} is uninitialized if this condition is met", self.name),
+                        ));
+                    }
+                }
+            }
+            hir::ExprKind::Match(_, arms, _) => {
+                // If the binding is initialized in one of the match arms, then the other match
+                // arms might be missing an initialization.
+                let results: Vec<bool> = arms
+                    .iter()
+                    .map(|arm| {
+                        let mut v = ReferencedStatementsVisitor(self.spans, false);
+                        v.visit_arm(arm);
+                        v.1
+                    })
+                    .collect();
+                if results.iter().any(|x| *x) && !results.iter().all(|x| *x) {
+                    for (arm, seen) in arms.iter().zip(results) {
+                        if !seen {
+                            self.errors.push((
+                                arm.pat.span,
+                                format!(
+                                    "{} is uninitialized if this pattern is matched",
+                                    self.name
+                                ),
+                            ));
+                        }
+                    }
+                }
+            }
+            // FIXME: should we also account for binops, particularly `&&` and `||`? `try` should
+            // also be accounted for. For now it is fine, as if we don't find *any* relevant
+            // branching code paths, we point at the places where the binding *is* initialized for
+            // *some* context. We should also specialize the output for `while` and `for` loops,
+            // but for now we can rely on their desugaring to provide appropriate output.
+            _ => {}
+        }
+        walk_expr(self, ex);
+    }
+}

src/test/ui/asm/x86_64/type-check-5.rs

@@ -13,10 +13,10 @@ fn main() {
 
         let x: u64;
         asm!("{}", in(reg) x);
-        //~^ ERROR use of possibly-uninitialized variable: `x`
+        //~^ ERROR E0381
         let mut y: u64;
         asm!("{}", inout(reg) y);
-        //~^ ERROR use of possibly-uninitialized variable: `y`
+        //~^ ERROR E0381
         let _ = y;
 
         // Outputs require mutable places

src/test/ui/asm/x86_64/type-check-5.stderr

@@ -1,14 +1,18 @@
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/type-check-5.rs:15:28
    |
+LL |         let x: u64;
+   |             - variable declared here
 LL |         asm!("{}", in(reg) x);
-   |                            ^ use of possibly-uninitialized `x`
+   |                            ^ `x` used here but it isn't initialized
 
-error[E0381]: use of possibly-uninitialized variable: `y`
+error[E0381]: binding `y` isn't initialized
   --> $DIR/type-check-5.rs:18:9
    |
+LL |         let mut y: u64;
+   |             ----- variable declared here
 LL |         asm!("{}", inout(reg) y);
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^ use of possibly-uninitialized `y`
+   |         ^^^^^^^^^^^^^^^^^^^^^^^^ `y` used here but it isn't initialized
 
 error[E0596]: cannot borrow `v` as mutable, as it is not declared as mutable
   --> $DIR/type-check-5.rs:26:29

src/test/ui/async-await/no-non-guaranteed-initialization.rs

@@ -6,8 +6,7 @@ async fn no_non_guaranteed_initialization(x: usize) -> usize {
     if x > 5 {
         y = echo(10).await;
     }
-    y
+    y //~ ERROR E0381
-    //~^ use of possibly-uninitialized variable: `y`
 }
 
 async fn echo(x: usize) -> usize { x + 1 }

src/test/ui/async-await/no-non-guaranteed-initialization.stderr

@@ -1,8 +1,13 @@
-error[E0381]: use of possibly-uninitialized variable: `y`
+error[E0381]: binding `y` isn't initialized in all conditions
   --> $DIR/no-non-guaranteed-initialization.rs:9:5
    |
+LL |     let y;
+   |         - variable declared here
+LL |     if x > 5 {
+   |        ----- this `if` expression might be missing an `else` arm where `y` is initialized
+...
 LL |     y
-   |     ^ use of possibly-uninitialized `y`
+   |     ^ `y` used here but it isn't initialized in all conditions
 
 error: aborting due to previous error
 

src/test/ui/async-await/partial-initialization-across-await.rs

@@ -10,8 +10,7 @@ async fn noop() {}
 
 async fn test_tuple() {
     let mut t: (i32, i32);
-    t.0 = 42;
+    t.0 = 42; //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `t` [E0381]
     noop().await;
     t.1 = 88;
     let _ = t;
@@ -19,8 +18,7 @@ async fn test_tuple() {
 
 async fn test_tuple_struct() {
     let mut t: T;
-    t.0 = 42;
+    t.0 = 42; //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `t` [E0381]
     noop().await;
     t.1 = 88;
     let _ = t;
@@ -28,8 +26,7 @@ async fn test_tuple_struct() {
 
 async fn test_struct() {
     let mut t: S;
-    t.x = 42;
+    t.x = 42; //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `t` [E0381]
     noop().await;
     t.y = 88;
     let _ = t;

src/test/ui/async-await/partial-initialization-across-await.stderr

@@ -1,20 +1,32 @@
-error[E0381]: assign to part of possibly-uninitialized variable: `t`
+error[E0381]: binding `t` isn't fully initialized
   --> $DIR/partial-initialization-across-await.rs:13:5
    |
+LL |     let mut t: (i32, i32);
+   |         ----- variable declared here
 LL |     t.0 = 42;
-   |     ^^^^^^^^ use of possibly-uninitialized `t`
+   |     ^^^^^^^^ `t` partially assigned here but it isn't fully initialized
-
-error[E0381]: assign to part of possibly-uninitialized variable: `t`
-  --> $DIR/partial-initialization-across-await.rs:22:5
    |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
+
+error[E0381]: binding `t` isn't fully initialized
+  --> $DIR/partial-initialization-across-await.rs:21:5
+   |
+LL |     let mut t: T;
+   |         ----- variable declared here
 LL |     t.0 = 42;
-   |     ^^^^^^^^ use of possibly-uninitialized `t`
+   |     ^^^^^^^^ `t` partially assigned here but it isn't fully initialized
-
-error[E0381]: assign to part of possibly-uninitialized variable: `t`
-  --> $DIR/partial-initialization-across-await.rs:31:5
    |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
+
+error[E0381]: binding `t` isn't fully initialized
+  --> $DIR/partial-initialization-across-await.rs:29:5
+   |
+LL |     let mut t: S;
+   |         ----- variable declared here
 LL |     t.x = 42;
-   |     ^^^^^^^^ use of possibly-uninitialized `t`
+   |     ^^^^^^^^ `t` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error: aborting due to 3 previous errors
 

src/test/ui/borrowck/assign_mutable_fields.stderr

@@ -1,14 +1,22 @@
-error[E0381]: assign to part of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't fully initialized
   --> $DIR/assign_mutable_fields.rs:9:5
    |
+LL |     let mut x: (u32, u32);
+   |         ----- variable declared here
 LL |     x.0 = 1;
-   |     ^^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^^ `x` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't fully initialized
   --> $DIR/assign_mutable_fields.rs:17:5
    |
+LL |     let mut x: (u32, u32);
+   |         ----- variable declared here
 LL |     x.0 = 1;
-   |     ^^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^^ `x` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error: aborting due to 2 previous errors
 

src/test/ui/borrowck/borrowck-and-init.rs

@@ -2,5 +2,5 @@ fn main() {
     let i: isize;
 
     println!("{}", false && { i = 5; true });
-    println!("{}", i); //~ ERROR borrow of possibly-uninitialized variable: `i`
+    println!("{}", i); //~ ERROR E0381
 }

src/test/ui/borrowck/borrowck-and-init.stderr

@@ -1,8 +1,13 @@
-error[E0381]: borrow of possibly-uninitialized variable: `i`
+error[E0381]: binding `i` isn't initialized in all conditions
   --> $DIR/borrowck-and-init.rs:5:20
    |
+LL |     let i: isize;
+   |         - variable declared here
+LL |
+LL |     println!("{}", false && { i = 5; true });
+   |                               ----- binding initialized here in some conditions
 LL |     println!("{}", i);
-   |                    ^ use of possibly-uninitialized `i`
+   |                    ^ `i` borrowed here but it isn't initialized in all conditions
    |
    = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/borrowck/borrowck-block-unint.rs

@@ -1,7 +1,7 @@
 fn force<F>(f: F) where F: FnOnce() { f(); }
 fn main() {
     let x: isize;
-    force(|| {  //~ ERROR borrow of possibly-uninitialized variable: `x`
+    force(|| {  //~ ERROR E0381
         println!("{}", x);
     });
 }

src/test/ui/borrowck/borrowck-block-unint.stderr

@@ -1,8 +1,10 @@
-error[E0381]: borrow of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-block-unint.rs:4:11
    |
+LL |     let x: isize;
+   |         - variable declared here
 LL |     force(|| {
-   |           ^^ use of possibly-uninitialized `x`
+   |           ^^ `x` borrowed here but it isn't initialized
 LL |         println!("{}", x);
    |                        - borrow occurs due to use in closure
 

src/test/ui/borrowck/borrowck-break-uninit-2.rs

@@ -6,7 +6,7 @@ fn foo() -> isize {
         x = 0;
     }
 
-    println!("{}", x); //~ ERROR borrow of possibly-uninitialized variable: `x`
+    println!("{}", x); //~ ERROR E0381
 
     return 17;
 }

src/test/ui/borrowck/borrowck-break-uninit-2.stderr

@@ -1,8 +1,11 @@
-error[E0381]: borrow of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-break-uninit-2.rs:9:20
    |
+LL |     let x: isize;
+   |         - variable declared here
+...
 LL |     println!("{}", x);
-   |                    ^ use of possibly-uninitialized `x`
+   |                    ^ `x` borrowed here but it isn't initialized
    |
    = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/borrowck/borrowck-break-uninit.rs

@@ -6,7 +6,7 @@ fn foo() -> isize {
         x = 0;
     }
 
-    println!("{}", x); //~ ERROR borrow of possibly-uninitialized variable: `x`
+    println!("{}", x); //~ ERROR E0381
 
     return 17;
 }

src/test/ui/borrowck/borrowck-break-uninit.stderr

@@ -1,8 +1,11 @@
-error[E0381]: borrow of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-break-uninit.rs:9:20
    |
+LL |     let x: isize;
+   |         - variable declared here
+...
 LL |     println!("{}", x);
-   |                    ^ use of possibly-uninitialized `x`
+   |                    ^ `x` borrowed here but it isn't initialized
    |
    = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/borrowck/borrowck-field-sensitivity.rs

@@ -78,20 +78,20 @@ fn fu_move_after_fu_move() {
 
 fn copy_after_field_assign_after_uninit() {
     let mut x: A;
-    x.a = 1; //~ ERROR assign to part of possibly-uninitialized variable: `x`
+    x.a = 1; //~ ERROR E0381
     drop(x.a);
 }
 
 fn borrow_after_field_assign_after_uninit() {
     let mut x: A;
-    x.a = 1; //~ ERROR assign to part of possibly-uninitialized variable: `x`
+    x.a = 1; //~ ERROR E0381
     let p = &x.a;
     drop(*p);
 }
 
 fn move_after_field_assign_after_uninit() {
     let mut x: A;
-    x.b = Box::new(1); //~ ERROR assign to part of possibly-uninitialized variable: `x`
+    x.b = Box::new(1); //~ ERROR E0381
     drop(x.b);
 }
 

src/test/ui/borrowck/borrowck-field-sensitivity.stderr

@@ -108,23 +108,35 @@ LL |     let _z = A { a: 4, .. x };
    |
    = note: move occurs because `x.b` has type `Box<isize>`, which does not implement the `Copy` trait
 
-error[E0381]: assign to part of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't fully initialized
   --> $DIR/borrowck-field-sensitivity.rs:81:5
    |
+LL |     let mut x: A;
+   |         ----- variable declared here
 LL |     x.a = 1;
-   |     ^^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^^ `x` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't fully initialized
   --> $DIR/borrowck-field-sensitivity.rs:87:5
    |
+LL |     let mut x: A;
+   |         ----- variable declared here
 LL |     x.a = 1;
-   |     ^^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^^ `x` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't fully initialized
   --> $DIR/borrowck-field-sensitivity.rs:94:5
    |
+LL |     let mut x: A;
+   |         ----- variable declared here
 LL |     x.b = Box::new(1);
-   |     ^^^ use of possibly-uninitialized `x`
+   |     ^^^ `x` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error: aborting due to 14 previous errors
 

src/test/ui/borrowck/borrowck-if-no-else.rs

@@ -2,5 +2,5 @@ fn foo(x: isize) { println!("{}", x); }
 
 fn main() {
     let x: isize; if 1 > 2 { x = 10; }
-    foo(x); //~ ERROR use of possibly-uninitialized variable: `x`
+    foo(x); //~ ERROR E0381
 }

src/test/ui/borrowck/borrowck-if-no-else.stderr

@@ -1,8 +1,12 @@
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized in all conditions
   --> $DIR/borrowck-if-no-else.rs:5:9
    |
+LL |     let x: isize; if 1 > 2 { x = 10; }
+   |         -            ----- this `if` expression might be missing an `else` arm where `x` is initialized
+   |         |
+   |         variable declared here
 LL |     foo(x);
-   |         ^ use of possibly-uninitialized `x`
+   |         ^ `x` used here but it isn't initialized in all conditions
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-if-with-else.rs

@@ -7,5 +7,5 @@ fn main() {
     } else {
         x = 10;
     }
-    foo(x); //~ ERROR use of possibly-uninitialized variable: `x`
+    foo(x); //~ ERROR E0381
 }

src/test/ui/borrowck/borrowck-if-with-else.stderr

@@ -1,8 +1,13 @@
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized in all conditions
   --> $DIR/borrowck-if-with-else.rs:10:9
    |
+LL |     let x: isize;
+   |         - variable declared here
+LL |     if 1 > 2 {
+   |        ----- `x` is uninitialized if this condition is met
+...
 LL |     foo(x);
-   |         ^ use of possibly-uninitialized `x`
+   |         ^ `x` used here but it isn't initialized in all conditions
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-init-in-called-fn-expr.rs

@@ -1,7 +1,7 @@
 fn main() {
     let j = || -> isize {
         let i: isize;
-        i //~ ERROR use of possibly-uninitialized variable: `i`
+        i //~ ERROR E0381
     };
     j();
 }

src/test/ui/borrowck/borrowck-init-in-called-fn-expr.stderr

@@ -1,8 +1,10 @@
-error[E0381]: use of possibly-uninitialized variable: `i`
+error[E0381]: binding `i` isn't initialized
   --> $DIR/borrowck-init-in-called-fn-expr.rs:4:9
    |
+LL |         let i: isize;
+   |             - variable declared here
 LL |         i
-   |         ^ use of possibly-uninitialized `i`
+   |         ^ `i` used here but it isn't initialized
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-init-in-fn-expr.rs

@@ -1,7 +1,7 @@
 fn main() {
     let f  = || -> isize {
         let i: isize;
-        i //~ ERROR use of possibly-uninitialized variable: `i`
+        i //~ ERROR E0381
     };
     println!("{}", f());
 }

src/test/ui/borrowck/borrowck-init-in-fn-expr.stderr

@@ -1,8 +1,10 @@
-error[E0381]: use of possibly-uninitialized variable: `i`
+error[E0381]: binding `i` isn't initialized
   --> $DIR/borrowck-init-in-fn-expr.rs:4:9
    |
+LL |         let i: isize;
+   |             - variable declared here
 LL |         i
-   |         ^ use of possibly-uninitialized `i`
+   |         ^ `i` used here but it isn't initialized
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-init-in-fru.rs

@@ -7,6 +7,6 @@ struct Point {
 fn main() {
     let mut origin: Point;
     origin = Point { x: 10, ..origin };
-    //~^ ERROR use of possibly-uninitialized variable: `origin` [E0381]
+    //~^ ERROR E0381
     origin.clone();
 }

src/test/ui/borrowck/borrowck-init-in-fru.stderr

@@ -1,8 +1,10 @@
-error[E0381]: use of possibly-uninitialized variable: `origin`
+error[E0381]: binding `origin.y` isn't initialized
   --> $DIR/borrowck-init-in-fru.rs:9:14
    |
+LL |     let mut origin: Point;
+   |         ---------- variable declared here
 LL |     origin = Point { x: 10, ..origin };
-   |              ^^^^^^^^^^^^^^^^^^^^^^^^^ use of possibly-uninitialized `origin.y`
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^ `origin.y` used here but it isn't initialized
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-init-op-equal.rs

@@ -1,6 +1,6 @@
 fn test() {
     let v: isize;
-    v += 1; //~ ERROR use of possibly-uninitialized variable: `v`
+    v += 1; //~ ERROR E0381
     v.clone();
 }
 

src/test/ui/borrowck/borrowck-init-op-equal.stderr

@@ -1,8 +1,10 @@
-error[E0381]: use of possibly-uninitialized variable: `v`
+error[E0381]: binding `v` isn't initialized
   --> $DIR/borrowck-init-op-equal.rs:3:5
    |
+LL |     let v: isize;
+   |         - variable declared here
 LL |     v += 1;
-   |     ^^^^^^ use of possibly-uninitialized `v`
+   |     ^^^^^^ `v` used here but it isn't initialized
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-init-plus-equal.rs

@@ -1,6 +1,6 @@
 fn test() {
     let mut v: isize;
-    v = v + 1; //~ ERROR use of possibly-uninitialized variable: `v`
+    v = v + 1; //~ ERROR E0381
     v.clone();
 }
 

src/test/ui/borrowck/borrowck-init-plus-equal.stderr

@@ -1,8 +1,10 @@
-error[E0381]: use of possibly-uninitialized variable: `v`
+error[E0381]: binding `v` isn't initialized
   --> $DIR/borrowck-init-plus-equal.rs:3:9
    |
+LL |     let mut v: isize;
+   |         ----- variable declared here
 LL |     v = v + 1;
-   |         ^ use of possibly-uninitialized `v`
+   |         ^ `v` used here but it isn't initialized
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-or-init.rs

@@ -2,5 +2,5 @@ fn main() {
     let i: isize;
 
     println!("{}", false || { i = 5; true });
-    println!("{}", i); //~ ERROR borrow of possibly-uninitialized variable: `i`
+    println!("{}", i); //~ ERROR E0381
 }

src/test/ui/borrowck/borrowck-or-init.stderr

@@ -1,8 +1,13 @@
-error[E0381]: borrow of possibly-uninitialized variable: `i`
+error[E0381]: binding `i` isn't initialized in all conditions
   --> $DIR/borrowck-or-init.rs:5:20
    |
+LL |     let i: isize;
+   |         - variable declared here
+LL |
+LL |     println!("{}", false || { i = 5; true });
+   |                               ----- binding initialized here in some conditions
 LL |     println!("{}", i);
-   |                    ^ use of possibly-uninitialized `i`
+   |                    ^ `i` borrowed here but it isn't initialized in all conditions
    |
    = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/borrowck/borrowck-partial-reinit-4.rs

@@ -14,8 +14,7 @@ impl Drop for Test2 {
 
 fn stuff() {
     let mut x : (Test2, Test2);
-    (x.0).0 = Some(Test);
+    (x.0).0 = Some(Test); //~ ERROR E0381
-    //~^ ERROR assign of possibly-uninitialized variable: `x.0`
 }
 
 fn main() {

src/test/ui/borrowck/borrowck-partial-reinit-4.stderr

@@ -1,8 +1,10 @@
-error[E0381]: assign of possibly-uninitialized variable: `x.0`
+error[E0381]: binding `x.0` isn't initialized
   --> $DIR/borrowck-partial-reinit-4.rs:17:5
    |
+LL |     let mut x : (Test2, Test2);
+   |         ----- variable declared here
 LL |     (x.0).0 = Some(Test);
-   |     ^^^^^^^ use of possibly-uninitialized `x.0`
+   |     ^^^^^^^ `x.0` assigned here but it isn't initialized
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-return.rs

@@ -1,6 +1,6 @@
 fn f() -> isize {
     let x: isize;
-    return x; //~ ERROR use of possibly-uninitialized variable: `x`
+    return x; //~ ERROR E0381
 }
 
 fn main() { f(); }

src/test/ui/borrowck/borrowck-return.stderr

@@ -1,8 +1,10 @@
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-return.rs:3:12
    |
+LL |     let x: isize;
+   |         - variable declared here
 LL |     return x;
-   |            ^ use of possibly-uninitialized `x`
+   |            ^ `x` used here but it isn't initialized
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-storage-dead.stderr

@@ -1,8 +1,10 @@
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-storage-dead.rs:16:17
    |
+LL |         let x: i32;
+   |             - variable declared here
 LL |         let _ = x + 1;
-   |                 ^ use of possibly-uninitialized `x`
+   |                 ^ `x` used here but it isn't initialized
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-uninit-after-item.rs

@@ -1,5 +1,5 @@
 fn main() {
     let bar;
     fn baz(_x: isize) { }
-    baz(bar); //~ ERROR use of possibly-uninitialized variable: `bar`
+    baz(bar); //~ ERROR E0381
 }

src/test/ui/borrowck/borrowck-uninit-after-item.stderr

@@ -1,8 +1,11 @@
-error[E0381]: use of possibly-uninitialized variable: `bar`
+error[E0381]: binding `bar` isn't initialized
   --> $DIR/borrowck-uninit-after-item.rs:4:9
    |
+LL |     let bar;
+   |         --- variable declared here
+LL |     fn baz(_x: isize) { }
 LL |     baz(bar);
-   |         ^^^ use of possibly-uninitialized `bar`
+   |         ^^^ `bar` used here but it isn't initialized
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-uninit-field-access.stderr

@@ -1,8 +1,10 @@
-error[E0381]: use of possibly-uninitialized variable: `a`
+error[E0381]: binding `a.x` isn't initialized
   --> $DIR/borrowck-uninit-field-access.rs:21:13
    |
+LL |     let mut a: Point;
+   |         ----- variable declared here
 LL |     let _ = a.x + 1;
-   |             ^^^ use of possibly-uninitialized `a.x`
+   |             ^^^ `a.x` used here but it isn't initialized
 
 error[E0382]: use of moved value: `line1.origin`
   --> $DIR/borrowck-uninit-field-access.rs:25:13

src/test/ui/borrowck/borrowck-uninit-in-assignop.rs

@@ -3,32 +3,32 @@
 
 pub fn main() {
     let x: isize;
-    x += 1; //~ ERROR use of possibly-uninitialized variable: `x`
+    x += 1; //~ ERROR E0381
 
     let x: isize;
-    x -= 1; //~ ERROR use of possibly-uninitialized variable: `x`
+    x -= 1; //~ ERROR E0381
 
     let x: isize;
-    x *= 1; //~ ERROR use of possibly-uninitialized variable: `x`
+    x *= 1; //~ ERROR E0381
 
     let x: isize;
-    x /= 1; //~ ERROR use of possibly-uninitialized variable: `x`
+    x /= 1; //~ ERROR E0381
 
     let x: isize;
-    x %= 1; //~ ERROR use of possibly-uninitialized variable: `x`
+    x %= 1; //~ ERROR E0381
 
     let x: isize;
-    x ^= 1; //~ ERROR use of possibly-uninitialized variable: `x`
+    x ^= 1; //~ ERROR E0381
 
     let x: isize;
-    x &= 1; //~ ERROR use of possibly-uninitialized variable: `x`
+    x &= 1; //~ ERROR E0381
 
     let x: isize;
-    x |= 1; //~ ERROR use of possibly-uninitialized variable: `x`
+    x |= 1; //~ ERROR E0381
 
     let x: isize;
-    x <<= 1;    //~ ERROR use of possibly-uninitialized variable: `x`
+    x <<= 1; //~ ERROR E0381
 
     let x: isize;
-    x >>= 1;    //~ ERROR use of possibly-uninitialized variable: `x`
+    x >>= 1; //~ ERROR E0381
 }

src/test/ui/borrowck/borrowck-uninit-in-assignop.stderr

@@ -1,62 +1,82 @@
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:6:5
    |
+LL |     let x: isize;
+   |         - variable declared here
 LL |     x += 1;
-   |     ^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^ `x` used here but it isn't initialized
 
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:9:5
    |
+LL |     let x: isize;
+   |         - variable declared here
 LL |     x -= 1;
-   |     ^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^ `x` used here but it isn't initialized
 
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:12:5
    |
+LL |     let x: isize;
+   |         - variable declared here
 LL |     x *= 1;
-   |     ^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^ `x` used here but it isn't initialized
 
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:15:5
    |
+LL |     let x: isize;
+   |         - variable declared here
 LL |     x /= 1;
-   |     ^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^ `x` used here but it isn't initialized
 
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:18:5
    |
+LL |     let x: isize;
+   |         - variable declared here
 LL |     x %= 1;
-   |     ^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^ `x` used here but it isn't initialized
 
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:21:5
    |
+LL |     let x: isize;
+   |         - variable declared here
 LL |     x ^= 1;
-   |     ^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^ `x` used here but it isn't initialized
 
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:24:5
    |
+LL |     let x: isize;
+   |         - variable declared here
 LL |     x &= 1;
-   |     ^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^ `x` used here but it isn't initialized
 
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:27:5
    |
+LL |     let x: isize;
+   |         - variable declared here
 LL |     x |= 1;
-   |     ^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^ `x` used here but it isn't initialized
 
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:30:5
    |
+LL |     let x: isize;
+   |         - variable declared here
 LL |     x <<= 1;
-   |     ^^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^^ `x` used here but it isn't initialized
 
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-uninit-in-assignop.rs:33:5
    |
+LL |     let x: isize;
+   |         - variable declared here
 LL |     x >>= 1;
-   |     ^^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^^ `x` used here but it isn't initialized
 
 error: aborting due to 10 previous errors
 

src/test/ui/borrowck/borrowck-uninit-ref-chain.rs

@@ -5,29 +5,29 @@ struct S<X, Y> {
 
 fn main() {
     let x: &&Box<i32>;
-    let _y = &**x; //~ [E0381]
+    let _y = &**x; //~ ERROR [E0381]
 
     let x: &&S<i32, i32>;
-    let _y = &**x; //~ [E0381]
+    let _y = &**x; //~ ERROR [E0381]
 
     let x: &&i32;
-    let _y = &**x; //~ [E0381]
+    let _y = &**x; //~ ERROR [E0381]
 
 
     let mut a: S<i32, i32>;
-    a.x = 0;            //~ ERROR assign to part of possibly-uninitialized variable: `a` [E0381]
+    a.x = 0; //~ ERROR [E0381]
     let _b = &a.x;
 
     let mut a: S<&&i32, &&i32>;
-    a.x = &&0;          //~ ERROR assign to part of possibly-uninitialized variable: `a` [E0381]
+    a.x = &&0; //~ ERROR [E0381]
     let _b = &**a.x;
 
 
     let mut a: S<i32, i32>;
-    a.x = 0;            //~ ERROR assign to part of possibly-uninitialized variable: `a` [E0381]
+    a.x = 0; //~ ERROR [E0381]
     let _b = &a.y;
 
     let mut a: S<&&i32, &&i32>;
-    a.x = &&0;          //~ assign to part of possibly-uninitialized variable: `a` [E0381]
+    a.x = &&0; //~ ERROR [E0381]
     let _b = &**a.y;
 }

src/test/ui/borrowck/borrowck-uninit-ref-chain.stderr

@@ -1,44 +1,66 @@
-error[E0381]: borrow of possibly-uninitialized variable: `x`
+error[E0381]: binding `**x` isn't initialized
   --> $DIR/borrowck-uninit-ref-chain.rs:8:14
    |
+LL |     let x: &&Box<i32>;
+   |         - variable declared here
 LL |     let _y = &**x;
-   |              ^^^^ use of possibly-uninitialized `**x`
+   |              ^^^^ `**x` borrowed here but it isn't initialized
 
-error[E0381]: borrow of possibly-uninitialized variable: `x`
+error[E0381]: binding `**x` isn't initialized
   --> $DIR/borrowck-uninit-ref-chain.rs:11:14
    |
+LL |     let x: &&S<i32, i32>;
+   |         - variable declared here
 LL |     let _y = &**x;
-   |              ^^^^ use of possibly-uninitialized `**x`
+   |              ^^^^ `**x` borrowed here but it isn't initialized
 
-error[E0381]: borrow of possibly-uninitialized variable: `x`
+error[E0381]: binding `**x` isn't initialized
   --> $DIR/borrowck-uninit-ref-chain.rs:14:14
    |
+LL |     let x: &&i32;
+   |         - variable declared here
 LL |     let _y = &**x;
-   |              ^^^^ use of possibly-uninitialized `**x`
+   |              ^^^^ `**x` borrowed here but it isn't initialized
 
-error[E0381]: assign to part of possibly-uninitialized variable: `a`
+error[E0381]: binding `a` isn't fully initialized
   --> $DIR/borrowck-uninit-ref-chain.rs:18:5
    |
+LL |     let mut a: S<i32, i32>;
+   |         ----- variable declared here
 LL |     a.x = 0;
-   |     ^^^^^^^ use of possibly-uninitialized `a`
+   |     ^^^^^^^ `a` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `a`
+error[E0381]: binding `a` isn't fully initialized
   --> $DIR/borrowck-uninit-ref-chain.rs:22:5
    |
+LL |     let mut a: S<&&i32, &&i32>;
+   |         ----- variable declared here
 LL |     a.x = &&0;
-   |     ^^^^^^^^^ use of possibly-uninitialized `a`
+   |     ^^^^^^^^^ `a` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `a`
+error[E0381]: binding `a` isn't fully initialized
   --> $DIR/borrowck-uninit-ref-chain.rs:27:5
    |
+LL |     let mut a: S<i32, i32>;
+   |         ----- variable declared here
 LL |     a.x = 0;
-   |     ^^^^^^^ use of possibly-uninitialized `a`
+   |     ^^^^^^^ `a` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `a`
+error[E0381]: binding `a` isn't fully initialized
   --> $DIR/borrowck-uninit-ref-chain.rs:31:5
    |
+LL |     let mut a: S<&&i32, &&i32>;
+   |         ----- variable declared here
 LL |     a.x = &&0;
-   |     ^^^^^^^^^ use of possibly-uninitialized `a`
+   |     ^^^^^^^^^ `a` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error: aborting due to 7 previous errors
 

src/test/ui/borrowck/borrowck-uninit.rs

@@ -2,5 +2,5 @@ fn foo(x: isize) { println!("{}", x); }
 
 fn main() {
     let x: isize;
-    foo(x); //~ ERROR use of possibly-uninitialized variable: `x`
+    foo(x); //~ ERROR E0381
 }

src/test/ui/borrowck/borrowck-uninit.stderr

@@ -1,8 +1,10 @@
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-uninit.rs:5:9
    |
+LL |     let x: isize;
+   |         - variable declared here
 LL |     foo(x);
-   |         ^ use of possibly-uninitialized `x`
+   |         ^ `x` used here but it isn't initialized
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-union-uninitialized.rs

@@ -10,8 +10,8 @@ fn main() {
     unsafe {
         let mut s: S;
         let mut u: U;
-        s.a = 0; //~ ERROR assign to part of possibly-uninitialized variable: `s`
+        s.a = 0; //~ ERROR E0381
-        u.a = 0; //~ ERROR assign to part of possibly-uninitialized variable: `u`
+        u.a = 0; //~ ERROR E0381
         let sa = s.a;
         let ua = u.a;
     }

src/test/ui/borrowck/borrowck-union-uninitialized.stderr

@@ -1,14 +1,24 @@
-error[E0381]: assign to part of possibly-uninitialized variable: `s`
+error[E0381]: binding `s` isn't fully initialized
   --> $DIR/borrowck-union-uninitialized.rs:13:9
    |
+LL |         let mut s: S;
+   |             ----- variable declared here
+LL |         let mut u: U;
 LL |         s.a = 0;
-   |         ^^^^^^^ use of possibly-uninitialized `s`
+   |         ^^^^^^^ `s` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `u`
+error[E0381]: binding `u` isn't fully initialized
   --> $DIR/borrowck-union-uninitialized.rs:14:9
    |
+LL |         let mut u: U;
+   |             ----- variable declared here
+LL |         s.a = 0;
 LL |         u.a = 0;
-   |         ^^^^^^^ use of possibly-uninitialized `u`
+   |         ^^^^^^^ `u` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error: aborting due to 2 previous errors
 

src/test/ui/borrowck/borrowck-use-in-index-lvalue.stderr

@@ -1,14 +1,18 @@
-error[E0381]: use of possibly-uninitialized variable: `w`
+error[E0381]: binding `*w` isn't initialized
   --> $DIR/borrowck-use-in-index-lvalue.rs:3:5
    |
+LL |     let w: &mut [isize];
+   |         - variable declared here
 LL |     w[5] = 0;
-   |     ^^^^ use of possibly-uninitialized `*w`
+   |     ^^^^ `*w` used here but it isn't initialized
 
-error[E0381]: use of possibly-uninitialized variable: `w`
+error[E0381]: binding `*w` isn't initialized
   --> $DIR/borrowck-use-in-index-lvalue.rs:6:5
    |
+LL |     let mut w: &mut [isize];
+   |         ----- variable declared here
 LL |     w[5] = 0;
-   |     ^^^^ use of possibly-uninitialized `*w`
+   |     ^^^^ `*w` used here but it isn't initialized
 
 error: aborting due to 2 previous errors
 

src/test/ui/borrowck/borrowck-use-uninitialized-in-cast-trait.stderr

@@ -1,8 +1,10 @@
-error[E0381]: borrow of possibly-uninitialized variable: `x`
+error[E0381]: binding `*x` isn't initialized
   --> $DIR/borrowck-use-uninitialized-in-cast-trait.rs:9:13
    |
+LL |     let x: &i32;
+   |         - variable declared here
 LL |     let y = x as *const dyn Foo;
-   |             ^ use of possibly-uninitialized `*x`
+   |             ^ `*x` borrowed here but it isn't initialized
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-use-uninitialized-in-cast.stderr

@@ -1,8 +1,10 @@
-error[E0381]: borrow of possibly-uninitialized variable: `x`
+error[E0381]: binding `*x` isn't initialized
   --> $DIR/borrowck-use-uninitialized-in-cast.rs:7:13
    |
+LL |     let x: &i32;
+   |         - variable declared here
 LL |     let y = x as *const i32;
-   |             ^ use of possibly-uninitialized `*x`
+   |             ^ `*x` borrowed here but it isn't initialized
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-while-break.rs

@@ -4,7 +4,7 @@ fn test(cond: bool) {
         v = 3;
         break;
     }
-    println!("{}", v); //~ ERROR borrow of possibly-uninitialized variable: `v`
+    println!("{}", v); //~ ERROR E0381
 }
 
 fn main() {

src/test/ui/borrowck/borrowck-while-break.stderr

@@ -1,8 +1,13 @@
-error[E0381]: borrow of possibly-uninitialized variable: `v`
+error[E0381]: binding `v` isn't initialized in all conditions
   --> $DIR/borrowck-while-break.rs:7:20
    |
+LL |     let v;
+   |         - variable declared here
+LL |     while cond {
+   |           ---- `v` is uninitialized if this condition isn't met
+...
 LL |     println!("{}", v);
-   |                    ^ use of possibly-uninitialized `v`
+   |                    ^ `v` borrowed here but it isn't initialized in all conditions
    |
    = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/borrowck/borrowck-while-cond.rs

@@ -1,4 +1,4 @@
 fn main() {
     let x: bool;
-    while x { } //~ ERROR use of possibly-uninitialized variable: `x`
+    while x { } //~ ERROR E0381
 }

src/test/ui/borrowck/borrowck-while-cond.stderr

@@ -1,8 +1,10 @@
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/borrowck-while-cond.rs:3:11
    |
+LL |     let x: bool;
+   |         - variable declared here
 LL |     while x { }
-   |           ^ use of possibly-uninitialized `x`
+   |           ^ `x` used here but it isn't initialized
 
 error: aborting due to previous error
 

src/test/ui/borrowck/borrowck-while.rs

@@ -1,7 +1,7 @@
 fn f() -> isize {
     let mut x: isize;
     while 1 == 1 { x = 10; }
-    return x; //~ ERROR use of possibly-uninitialized variable: `x`
+    return x; //~ ERROR E0381
 }
 
 fn main() { f(); }

src/test/ui/borrowck/borrowck-while.stderr

@@ -1,8 +1,12 @@
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized in all conditions
   --> $DIR/borrowck-while.rs:4:12
    |
+LL |     let mut x: isize;
+   |         ----- variable declared here
+LL |     while 1 == 1 { x = 10; }
+   |           ------ `x` is uninitialized if this condition isn't met
 LL |     return x;
-   |            ^ use of possibly-uninitialized `x`
+   |            ^ `x` used here but it isn't initialized in all conditions
 
 error: aborting due to previous error
 

src/test/ui/borrowck/disallow-possibly-uninitialized.rs

@@ -4,19 +4,19 @@
 fn main() {
     let mut t: (u64, u64);
     t.0 = 1;
-    //~^ ERROR assign to part of possibly-uninitialized variable: `t` [E0381]
+    //~^ ERROR E0381
     t.1 = 1;
 
     let mut t: (u64, u64);
     t.1 = 1;
-    //~^ ERROR assign to part of possibly-uninitialized variable: `t` [E0381]
+    //~^ ERROR E0381
     t.0 = 1;
 
     let mut t: (u64, u64);
     t.0 = 1;
-    //~^ ERROR assign to part of possibly-uninitialized variable: `t` [E0381]
+    //~^ ERROR E0381
 
     let mut t: (u64,);
     t.0 = 1;
-    //~^ ERROR assign to part of possibly-uninitialized variable: `t` [E0381]
+    //~^ ERROR E0381
 }

src/test/ui/borrowck/disallow-possibly-uninitialized.stderr

@@ -1,26 +1,42 @@
-error[E0381]: assign to part of possibly-uninitialized variable: `t`
+error[E0381]: binding `t` isn't fully initialized
   --> $DIR/disallow-possibly-uninitialized.rs:6:5
    |
+LL |     let mut t: (u64, u64);
+   |         ----- variable declared here
 LL |     t.0 = 1;
-   |     ^^^^^^^ use of possibly-uninitialized `t`
+   |     ^^^^^^^ `t` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `t`
+error[E0381]: binding `t` isn't fully initialized
   --> $DIR/disallow-possibly-uninitialized.rs:11:5
    |
+LL |     let mut t: (u64, u64);
+   |         ----- variable declared here
 LL |     t.1 = 1;
-   |     ^^^^^^^ use of possibly-uninitialized `t`
+   |     ^^^^^^^ `t` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `t`
+error[E0381]: binding `t` isn't fully initialized
   --> $DIR/disallow-possibly-uninitialized.rs:16:5
    |
+LL |     let mut t: (u64, u64);
+   |         ----- variable declared here
 LL |     t.0 = 1;
-   |     ^^^^^^^ use of possibly-uninitialized `t`
+   |     ^^^^^^^ `t` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `t`
+error[E0381]: binding `t` isn't fully initialized
   --> $DIR/disallow-possibly-uninitialized.rs:20:5
    |
+LL |     let mut t: (u64,);
+   |         ----- variable declared here
 LL |     t.0 = 1;
-   |     ^^^^^^^ use of possibly-uninitialized `t`
+   |     ^^^^^^^ `t` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error: aborting due to 4 previous errors
 

src/test/ui/borrowck/issue-24267-flow-exit.rs

@@ -9,11 +9,11 @@ pub fn main() {
 pub fn foo1() {
     let x: i32;
     loop { x = break; }
-    println!("{}", x); //~ ERROR borrow of possibly-uninitialized variable: `x`
+    println!("{}", x); //~ ERROR E0381
 }
 
 pub fn foo2() {
     let x: i32;
     for _ in 0..10 { x = continue; }
-    println!("{}", x); //~ ERROR borrow of possibly-uninitialized variable: `x`
+    println!("{}", x); //~ ERROR E0381
 }

src/test/ui/borrowck/issue-24267-flow-exit.stderr

@@ -1,16 +1,22 @@
-error[E0381]: borrow of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/issue-24267-flow-exit.rs:12:20
    |
+LL |     let x: i32;
+   |         - variable declared here
+LL |     loop { x = break; }
 LL |     println!("{}", x);
-   |                    ^ use of possibly-uninitialized `x`
+   |                    ^ `x` borrowed here but it isn't initialized
    |
    = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0381]: borrow of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/issue-24267-flow-exit.rs:18:20
    |
+LL |     let x: i32;
+   |         - variable declared here
+LL |     for _ in 0..10 { x = continue; }
 LL |     println!("{}", x);
-   |                    ^ use of possibly-uninitialized `x`
+   |                    ^ `x` borrowed here but it isn't initialized
    |
    = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/borrowck/issue-54499-field-mutation-marks-mut-as-used.rs

@@ -10,7 +10,7 @@ fn main() {
     {
         let mut t: Tuple;
         t.0 = S(1);
-        //~^ ERROR assign to part of possibly-uninitialized variable: `t` [E0381]
+        //~^ ERROR E0381
         t.1 = 2;
         println!("{:?} {:?}", t.0, t.1);
     }
@@ -18,7 +18,7 @@ fn main() {
     {
         let mut u: Tpair;
         u.0 = S(1);
-        //~^ ERROR assign to part of possibly-uninitialized variable: `u` [E0381]
+        //~^ ERROR E0381
         u.1 = 2;
         println!("{:?} {:?}", u.0, u.1);
     }
@@ -26,7 +26,7 @@ fn main() {
     {
         let mut v: Spair;
         v.x = S(1);
-        //~^ ERROR assign to part of possibly-uninitialized variable: `v` [E0381]
+        //~^ ERROR E0381
         v.y = 2;
         println!("{:?} {:?}", v.x, v.y);
     }

src/test/ui/borrowck/issue-54499-field-mutation-marks-mut-as-used.stderr

@@ -1,20 +1,32 @@
-error[E0381]: assign to part of possibly-uninitialized variable: `t`
+error[E0381]: binding `t` isn't fully initialized
   --> $DIR/issue-54499-field-mutation-marks-mut-as-used.rs:12:9
    |
+LL |         let mut t: Tuple;
+   |             ----- variable declared here
 LL |         t.0 = S(1);
-   |         ^^^^^^^^^^ use of possibly-uninitialized `t`
+   |         ^^^^^^^^^^ `t` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `u`
+error[E0381]: binding `u` isn't fully initialized
   --> $DIR/issue-54499-field-mutation-marks-mut-as-used.rs:20:9
    |
+LL |         let mut u: Tpair;
+   |             ----- variable declared here
 LL |         u.0 = S(1);
-   |         ^^^^^^^^^^ use of possibly-uninitialized `u`
+   |         ^^^^^^^^^^ `u` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `v`
+error[E0381]: binding `v` isn't fully initialized
   --> $DIR/issue-54499-field-mutation-marks-mut-as-used.rs:28:9
    |
+LL |         let mut v: Spair;
+   |             ----- variable declared here
 LL |         v.x = S(1);
-   |         ^^^^^^^^^^ use of possibly-uninitialized `v`
+   |         ^^^^^^^^^^ `v` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error: aborting due to 3 previous errors
 

src/test/ui/borrowck/issue-54499-field-mutation-of-never-init.rs

@@ -10,7 +10,7 @@ fn main() {
     {
         let t: Tuple;
         t.0 = S(1);
-        //~^ ERROR assign to part of possibly-uninitialized variable: `t` [E0381]
+        //~^ ERROR E0381
         t.1 = 2;
         println!("{:?} {:?}", t.0, t.1);
     }
@@ -18,7 +18,7 @@ fn main() {
     {
         let u: Tpair;
         u.0 = S(1);
-        //~^ ERROR assign to part of possibly-uninitialized variable: `u` [E0381]
+        //~^ ERROR E0381
         u.1 = 2;
         println!("{:?} {:?}", u.0, u.1);
     }
@@ -26,7 +26,7 @@ fn main() {
     {
         let v: Spair;
         v.x = S(1);
-        //~^ ERROR assign to part of possibly-uninitialized variable: `v` [E0381]
+        //~^ ERROR E0381
         v.y = 2;
         println!("{:?} {:?}", v.x, v.y);
     }

src/test/ui/borrowck/issue-54499-field-mutation-of-never-init.stderr

@@ -1,20 +1,32 @@
-error[E0381]: assign to part of possibly-uninitialized variable: `t`
+error[E0381]: binding `t` isn't fully initialized
   --> $DIR/issue-54499-field-mutation-of-never-init.rs:12:9
    |
+LL |         let t: Tuple;
+   |             - variable declared here
 LL |         t.0 = S(1);
-   |         ^^^^^^^^^^ use of possibly-uninitialized `t`
+   |         ^^^^^^^^^^ `t` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `u`
+error[E0381]: binding `u` isn't fully initialized
   --> $DIR/issue-54499-field-mutation-of-never-init.rs:20:9
    |
+LL |         let u: Tpair;
+   |             - variable declared here
 LL |         u.0 = S(1);
-   |         ^^^^^^^^^^ use of possibly-uninitialized `u`
+   |         ^^^^^^^^^^ `u` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `v`
+error[E0381]: binding `v` isn't fully initialized
   --> $DIR/issue-54499-field-mutation-of-never-init.rs:28:9
    |
+LL |         let v: Spair;
+   |             - variable declared here
 LL |         v.x = S(1);
-   |         ^^^^^^^^^^ use of possibly-uninitialized `v`
+   |         ^^^^^^^^^^ `v` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error: aborting due to 3 previous errors
 

src/test/ui/borrowck/issue-62107-match-arm-scopes.rs

@@ -1,7 +1,7 @@
 fn main() {
     let e: i32;
     match e {
-        //~^ ERROR use of possibly-uninitialized variable
+        //~^ ERROR E0381
         ref u if true => {}
         ref v if true => {
             let tx = 0;

src/test/ui/borrowck/issue-62107-match-arm-scopes.stderr

@@ -1,8 +1,10 @@
-error[E0381]: use of possibly-uninitialized variable: `e`
+error[E0381]: binding `e` isn't initialized
   --> $DIR/issue-62107-match-arm-scopes.rs:3:11
    |
+LL |     let e: i32;
+   |         - variable declared here
 LL |     match e {
-   |           ^ use of possibly-uninitialized `e`
+   |           ^ `e` used here but it isn't initialized
 
 error: aborting due to previous error
 

src/test/ui/borrowck/reassignment_immutable_fields.stderr

@@ -1,14 +1,22 @@
-error[E0381]: assign to part of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't fully initialized
   --> $DIR/reassignment_immutable_fields.rs:7:5
    |
+LL |     let x: (u32, u32);
+   |         - variable declared here
 LL |     x.0 = 1;
-   |     ^^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^^ `x` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't fully initialized
   --> $DIR/reassignment_immutable_fields.rs:15:5
    |
+LL |     let x: (u32, u32);
+   |         - variable declared here
 LL |     x.0 = 1;
-   |     ^^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^^ `x` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error: aborting due to 2 previous errors
 

src/test/ui/borrowck/reassignment_immutable_fields_overlapping.stderr

@@ -1,8 +1,12 @@
-error[E0381]: assign to part of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't fully initialized
   --> $DIR/reassignment_immutable_fields_overlapping.rs:12:5
    |
+LL |     let x: Foo;
+   |         - variable declared here
 LL |     x.a = 1;
-   |     ^^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^^ `x` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error[E0594]: cannot assign to `x.b`, as `x` is not declared as mutable
   --> $DIR/reassignment_immutable_fields_overlapping.rs:13:5

src/test/ui/borrowck/reassignment_immutable_fields_twice.stderr

@@ -7,11 +7,15 @@ LL |     x = (22, 44);
 LL |     x.0 = 1;
    |     ^^^^^^^ cannot assign
 
-error[E0381]: assign to part of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't fully initialized
   --> $DIR/reassignment_immutable_fields_twice.rs:12:5
    |
+LL |     let x: (u32, u32);
+   |         - variable declared here
 LL |     x.0 = 1;
-   |     ^^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^^ `x` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error: aborting due to 2 previous errors
 

src/test/ui/closures/2229_closure_analysis/match/pattern-matching-should-fail.rs

@@ -6,14 +6,14 @@
 fn test1() {
     let x: !;
     let c1 = || match x { };
-    //~^ ERROR: use of possibly-uninitialized variable: `x`
+    //~^ ERROR E0381
 }
 
 // Should fake read the discriminant and throw an error
 fn test2() {
     let x: !;
     let c2 = || match x { _ => () };
-    //~^ ERROR: borrow of possibly-uninitialized variable: `x`
+    //~^ ERROR E0381
 }
 
 // Testing single variant patterns
@@ -25,7 +25,7 @@ enum SingleVariant {
 fn test3() {
     let variant: !;
     let c = || {
-    //~^ ERROR: borrow of possibly-uninitialized variable: `variant`
+    //~^ ERROR E0381
         match variant {
             SingleVariant::Points(_) => {}
         }
@@ -36,8 +36,7 @@ fn test3() {
 // Should fake read the discriminant and throw an error
 fn test4() {
     let variant: !;
-    let c = || {
+    let c = || { //~ ERROR E0381
-    //~^ ERROR: borrow of possibly-uninitialized variable: `variant`
         match variant {
             SingleVariant::Points(a) => {
                 println!("{:?}", a);
@@ -52,11 +51,9 @@ fn test5() {
     let g: !;
 
     let a = || {
-        match g { };
+        match g { }; //~ ERROR E0381
-        //~^ ERROR: use of possibly-uninitialized variable: `g`
         let c = ||  {
-            match t { };
+            match t { }; //~ ERROR E0381
-            //~^ ERROR: use of possibly-uninitialized variable: `t`
         };
 
         c();
@@ -68,7 +65,7 @@ fn test5() {
 fn test6() {
     let x: u8;
     let c1 = || match x { };
-    //~^ ERROR: use of possibly-uninitialized variable: `x`
+    //~^ ERROR E0381
     //~| ERROR: non-exhaustive patterns: type `u8` is non-empty
 }
 

src/test/ui/closures/2229_closure_analysis/match/pattern-matching-should-fail.stderr

@@ -1,5 +1,5 @@
 error[E0004]: non-exhaustive patterns: type `u8` is non-empty
-  --> $DIR/pattern-matching-should-fail.rs:70:23
+  --> $DIR/pattern-matching-should-fail.rs:67:23
    |
 LL |     let c1 = || match x { };
    |                       ^
@@ -12,55 +12,70 @@ LL +         _ => todo!(),
 LL ~     };
    |
 
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/pattern-matching-should-fail.rs:8:23
    |
+LL |     let x: !;
+   |         - variable declared here
 LL |     let c1 = || match x { };
-   |                       ^ use of possibly-uninitialized `x`
+   |                       ^ `x` used here but it isn't initialized
 
-error[E0381]: borrow of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/pattern-matching-should-fail.rs:15:14
    |
+LL |     let x: !;
+   |         - variable declared here
 LL |     let c2 = || match x { _ => () };
    |              ^^       - borrow occurs due to use in closure
    |              |
-   |              use of possibly-uninitialized `x`
+   |              `x` borrowed here but it isn't initialized
 
-error[E0381]: borrow of possibly-uninitialized variable: `variant`
+error[E0381]: binding `variant` isn't initialized
   --> $DIR/pattern-matching-should-fail.rs:27:13
    |
+LL |     let variant: !;
+   |         ------- variable declared here
 LL |     let c = || {
-   |             ^^ use of possibly-uninitialized `variant`
+   |             ^^ `variant` borrowed here but it isn't initialized
 LL |
 LL |         match variant {
    |               ------- borrow occurs due to use in closure
 
-error[E0381]: borrow of possibly-uninitialized variable: `variant`
+error[E0381]: binding `variant` isn't initialized
   --> $DIR/pattern-matching-should-fail.rs:39:13
    |
+LL |     let variant: !;
+   |         ------- variable declared here
 LL |     let c = || {
-   |             ^^ use of possibly-uninitialized `variant`
+   |             ^^ `variant` borrowed here but it isn't initialized
-LL |
 LL |         match variant {
    |               ------- borrow occurs due to use in closure
 
-error[E0381]: use of possibly-uninitialized variable: `g`
+error[E0381]: binding `g` isn't initialized
-  --> $DIR/pattern-matching-should-fail.rs:55:15
+  --> $DIR/pattern-matching-should-fail.rs:54:15
    |
+LL |     let g: !;
+   |         - variable declared here
+...
 LL |         match g { };
-   |               ^ use of possibly-uninitialized `g`
+   |               ^ `g` used here but it isn't initialized
 
-error[E0381]: use of possibly-uninitialized variable: `t`
+error[E0381]: binding `t` isn't initialized
-  --> $DIR/pattern-matching-should-fail.rs:58:19
+  --> $DIR/pattern-matching-should-fail.rs:56:19
    |
+LL |     let t: !;
+   |         - variable declared here
+...
 LL |             match t { };
-   |                   ^ use of possibly-uninitialized `t`
+   |                   ^ `t` used here but it isn't initialized
 
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
-  --> $DIR/pattern-matching-should-fail.rs:70:23
+  --> $DIR/pattern-matching-should-fail.rs:67:23
    |
+LL |     let x: u8;
+   |         - variable declared here
 LL |     let c1 = || match x { };
-   |                       ^ use of possibly-uninitialized `x`
+   |                       ^ `x` used here but it isn't initialized
 
 error: aborting due to 8 previous errors
 

src/test/ui/const-generics/const-generic-default-wont-borrowck.rs

@@ -1,6 +1,5 @@
 struct X<const N: usize = {
-    let s: &'static str; s.len()
+    let s: &'static str; s.len() //~ ERROR E0381
-    //~^ ERROR borrow of possibly-uninitialized variable
 }>;
 
 fn main() {}

src/test/ui/const-generics/const-generic-default-wont-borrowck.stderr

@@ -1,8 +1,10 @@
-error[E0381]: borrow of possibly-uninitialized variable: `s`
+error[E0381]: binding `*s` isn't initialized
   --> $DIR/const-generic-default-wont-borrowck.rs:2:26
    |
 LL |     let s: &'static str; s.len()
-   |                          ^^^^^^^ use of possibly-uninitialized `*s`
+   |         -                ^^^^^^^ `*s` borrowed here but it isn't initialized
+   |         |
+   |         variable declared here
 
 error: aborting due to previous error
 

src/test/ui/consts/issue-78655.rs

@@ -1,6 +1,6 @@
 const FOO: *const u32 = {
     let x;
-    &x //~ ERROR borrow of possibly-uninitialized variable: `x`
+    &x //~ ERROR E0381
 };
 
 fn main() {

src/test/ui/consts/issue-78655.stderr

@@ -1,8 +1,10 @@
-error[E0381]: borrow of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/issue-78655.rs:3:5
    |
+LL |     let x;
+   |         - variable declared here
 LL |     &x
-   |     ^^ use of possibly-uninitialized `x`
+   |     ^^ `x` borrowed here but it isn't initialized
 
 error: could not evaluate constant pattern
   --> $DIR/issue-78655.rs:7:9

src/test/ui/drop/repeat-drop-2.rs

@@ -9,7 +9,7 @@ const _: [String; 0] = [String::new(); 0];
 
 fn must_be_init() {
     let x: u8;
-    let _ = [x; 0]; //~ ERROR: use of possibly-uninitialized variable: `x`
+    let _ = [x; 0]; //~ ERROR E0381
 }
 
 fn main() {}

src/test/ui/drop/repeat-drop-2.stderr

@@ -17,11 +17,13 @@ LL | const _: [String; 0] = [String::new(); 0];
    |                        |constants cannot evaluate destructors
    |                        value is dropped here
 
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/repeat-drop-2.rs:12:14
    |
+LL |     let x: u8;
+   |         - variable declared here
 LL |     let _ = [x; 0];
-   |              ^ use of possibly-uninitialized `x`
+   |              ^ `x` used here but it isn't initialized
 
 error: aborting due to 3 previous errors
 

src/test/ui/generator/partial-initialization-across-yield.rs

@@ -9,8 +9,7 @@ struct T(i32, i32);
 fn test_tuple() {
     let _ = || {
         let mut t: (i32, i32);
-        t.0 = 42;
+        t.0 = 42; //~ ERROR E0381
-        //~^ ERROR assign to part of possibly-uninitialized variable: `t` [E0381]
         yield;
         t.1 = 88;
         let _ = t;
@@ -20,8 +19,7 @@ fn test_tuple() {
 fn test_tuple_struct() {
     let _ = || {
         let mut t: T;
-        t.0 = 42;
+        t.0 = 42; //~ ERROR E0381
-        //~^ ERROR assign to part of possibly-uninitialized variable: `t` [E0381]
         yield;
         t.1 = 88;
         let _ = t;
@@ -31,8 +29,7 @@ fn test_tuple_struct() {
 fn test_struct() {
     let _ = || {
         let mut t: S;
-        t.x = 42;
+        t.x = 42; //~ ERROR E0381
-        //~^ ERROR assign to part of possibly-uninitialized variable: `t` [E0381]
         yield;
         t.y = 88;
         let _ = t;

src/test/ui/generator/partial-initialization-across-yield.stderr

@@ -1,20 +1,32 @@
-error[E0381]: assign to part of possibly-uninitialized variable: `t`
+error[E0381]: binding `t` isn't fully initialized
   --> $DIR/partial-initialization-across-yield.rs:12:9
    |
+LL |         let mut t: (i32, i32);
+   |             ----- variable declared here
 LL |         t.0 = 42;
-   |         ^^^^^^^^ use of possibly-uninitialized `t`
+   |         ^^^^^^^^ `t` partially assigned here but it isn't fully initialized
-
-error[E0381]: assign to part of possibly-uninitialized variable: `t`
-  --> $DIR/partial-initialization-across-yield.rs:23:9
    |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
+
+error[E0381]: binding `t` isn't fully initialized
+  --> $DIR/partial-initialization-across-yield.rs:22:9
+   |
+LL |         let mut t: T;
+   |             ----- variable declared here
 LL |         t.0 = 42;
-   |         ^^^^^^^^ use of possibly-uninitialized `t`
+   |         ^^^^^^^^ `t` partially assigned here but it isn't fully initialized
-
-error[E0381]: assign to part of possibly-uninitialized variable: `t`
-  --> $DIR/partial-initialization-across-yield.rs:34:9
    |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
+
+error[E0381]: binding `t` isn't fully initialized
+  --> $DIR/partial-initialization-across-yield.rs:32:9
+   |
+LL |         let mut t: S;
+   |             ----- variable declared here
 LL |         t.x = 42;
-   |         ^^^^^^^^ use of possibly-uninitialized `t`
+   |         ^^^^^^^^ `t` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error: aborting due to 3 previous errors
 

src/test/ui/loops/loop-proper-liveness.rs

@@ -6,7 +6,7 @@ fn test1() {
     'a: loop {
         x = loop { break 'a };
     }
-    println!("{:?}", x); //~ ERROR borrow of possibly-uninitialized variable
+    println!("{:?}", x); //~ ERROR E0381
 }
 
 // test2 and test3 should not fail.

src/test/ui/loops/loop-proper-liveness.stderr

@@ -1,8 +1,11 @@
-error[E0381]: borrow of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/loop-proper-liveness.rs:9:22
    |
+LL |     let x: i32;
+   |         - variable declared here
+...
 LL |     println!("{:?}", x);
-   |                      ^ use of possibly-uninitialized `x`
+   |                      ^ `x` borrowed here but it isn't initialized
    |
    = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/mir/drop-elaboration-after-borrowck-error.rs

@@ -6,7 +6,7 @@ static A: () = {
     //~^ ERROR destructors cannot be evaluated at compile-time
     a[0] = String::new();
     //~^ ERROR destructors cannot be evaluated at compile-time
-    //~| ERROR use of possibly-uninitialized variable
+    //~| ERROR binding `a` isn't initialized
 };
 
 struct B<T>([T; 1]);

src/test/ui/mir/drop-elaboration-after-borrowck-error.stderr

@@ -16,11 +16,14 @@ LL |     let a: [String; 1];
 LL | };
    | - value is dropped here
 
-error[E0381]: use of possibly-uninitialized variable: `a`
+error[E0381]: binding `a` isn't initialized
   --> $DIR/drop-elaboration-after-borrowck-error.rs:7:5
    |
+LL |     let a: [String; 1];
+   |         - variable declared here
+LL |
 LL |     a[0] = String::new();
-   |     ^^^^ use of possibly-uninitialized `a`
+   |     ^^^^ `a` used here but it isn't initialized
 
 error[E0493]: destructors cannot be evaluated at compile-time
   --> $DIR/drop-elaboration-after-borrowck-error.rs:18:9

src/test/ui/moves/issue-72649-uninit-in-loop.rs

@@ -57,17 +57,17 @@ fn moved_loop_2() {
 
 fn uninit_1() {
     loop {
-        let value: NonCopy;
+        let value: NonCopy; //~ NOTE variable declared here
-        let _used = value; //~ ERROR use of possibly-uninitialized variable: `value`
+        let _used = value; //~ ERROR binding `value` isn't initialized
-        //~^ NOTE use of possibly-uninitialized `value`
+        //~^ NOTE `value` used here but it isn't initialized
     }
 }
 
 fn uninit_2() {
-    let mut value: NonCopy;
+    let mut value: NonCopy; //~ NOTE variable declared here
     loop {
-        let _used = value; //~ ERROR use of possibly-uninitialized variable: `value`
+        let _used = value; //~ ERROR binding `value` isn't initialized
-        //~^ NOTE use of possibly-uninitialized `value`
+        //~^ NOTE `value` used here but it isn't initialized
     }
 }
 

src/test/ui/moves/issue-72649-uninit-in-loop.stderr

@@ -40,17 +40,22 @@ LL |     let mut value = NonCopy{};
 LL |         let _used2 = value;
    |                      ^^^^^ value moved here, in previous iteration of loop
 
-error[E0381]: use of possibly-uninitialized variable: `value`
+error[E0381]: binding `value` isn't initialized
   --> $DIR/issue-72649-uninit-in-loop.rs:61:21
    |
+LL |         let value: NonCopy;
+   |             ----- variable declared here
 LL |         let _used = value;
-   |                     ^^^^^ use of possibly-uninitialized `value`
+   |                     ^^^^^ `value` used here but it isn't initialized
 
-error[E0381]: use of possibly-uninitialized variable: `value`
+error[E0381]: binding `value` isn't initialized
   --> $DIR/issue-72649-uninit-in-loop.rs:69:21
    |
+LL |     let mut value: NonCopy;
+   |         --------- variable declared here
+LL |     loop {
 LL |         let _used = value;
-   |                     ^^^^^ use of possibly-uninitialized `value`
+   |                     ^^^^^ `value` used here but it isn't initialized
 
 error: aborting due to 6 previous errors
 

src/test/ui/moves/move-into-dead-array-1.rs

@@ -11,5 +11,5 @@ fn main() {
 
 fn foo(i: usize) {
     let mut a: [D; 4];
-    a[i] = d();        //~ ERROR use of possibly-uninitialized variable: `a`
+    a[i] = d(); //~ ERROR E0381
 }

src/test/ui/moves/move-into-dead-array-1.stderr

@@ -1,8 +1,10 @@
-error[E0381]: use of possibly-uninitialized variable: `a`
+error[E0381]: binding `a` isn't initialized
   --> $DIR/move-into-dead-array-1.rs:14:5
    |
+LL |     let mut a: [D; 4];
+   |         ----- variable declared here
 LL |     a[i] = d();
-   |     ^^^^ use of possibly-uninitialized `a`
+   |     ^^^^ `a` used here but it isn't initialized
 
 error: aborting due to previous error
 

src/test/ui/moves/move-of-addr-of-mut.rs

@@ -5,7 +5,7 @@ struct S;
 
 fn main() {
     let mut x: S;
-    std::ptr::addr_of_mut!(x); //~ borrow of
+    std::ptr::addr_of_mut!(x); //~ ERROR E0381
 
     let y = x; // Should error here if `addr_of_mut` is ever allowed on uninitialized variables
     drop(y);

src/test/ui/moves/move-of-addr-of-mut.stderr

@@ -1,8 +1,10 @@
-error[E0381]: borrow of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized
   --> $DIR/move-of-addr-of-mut.rs:8:5
    |
+LL |     let mut x: S;
+   |         ----- variable declared here
 LL |     std::ptr::addr_of_mut!(x);
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ use of possibly-uninitialized `x`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^ `x` borrowed here but it isn't initialized
    |
    = note: this error originates in the macro `std::ptr::addr_of_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
 

src/test/ui/nll/issue-21232-partial-init-and-erroneous-use.rs

@@ -25,14 +25,12 @@ impl Drop for D {
 
 fn cannot_partially_init_adt_with_drop() {
     let d: D;
-    d.x = 10;
+    d.x = 10; //~ ERROR E0381
-    //~^ ERROR assign of possibly-uninitialized variable: `d` [E0381]
 }
 
 fn cannot_partially_init_mutable_adt_with_drop() {
     let mut d: D;
-    d.x = 10;
+    d.x = 10; //~ ERROR E0381
-    //~^ ERROR assign of possibly-uninitialized variable: `d` [E0381]
 }
 
 fn cannot_partially_reinit_adt_with_drop() {
@@ -44,14 +42,12 @@ fn cannot_partially_reinit_adt_with_drop() {
 
 fn cannot_partially_init_inner_adt_via_outer_with_drop() {
     let d: D;
-    d.s.y = 20;
+    d.s.y = 20; //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `d` [E0381]
 }
 
 fn cannot_partially_init_inner_adt_via_mutable_outer_with_drop() {
     let mut d: D;
-    d.s.y = 20;
+    d.s.y = 20; //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `d` [E0381]
 }
 
 fn cannot_partially_reinit_inner_adt_via_outer_with_drop() {

src/test/ui/nll/issue-21232-partial-init-and-erroneous-use.stderr

@@ -1,17 +1,21 @@
-error[E0381]: assign of possibly-uninitialized variable: `d`
+error[E0381]: binding `d` isn't initialized
   --> $DIR/issue-21232-partial-init-and-erroneous-use.rs:28:5
    |
+LL |     let d: D;
+   |         - variable declared here
 LL |     d.x = 10;
-   |     ^^^^^^^^ use of possibly-uninitialized `d`
+   |     ^^^^^^^^ `d` assigned here but it isn't initialized
 
-error[E0381]: assign of possibly-uninitialized variable: `d`
+error[E0381]: binding `d` isn't initialized
-  --> $DIR/issue-21232-partial-init-and-erroneous-use.rs:34:5
+  --> $DIR/issue-21232-partial-init-and-erroneous-use.rs:33:5
    |
+LL |     let mut d: D;
+   |         ----- variable declared here
 LL |     d.x = 10;
-   |     ^^^^^^^^ use of possibly-uninitialized `d`
+   |     ^^^^^^^^ `d` assigned here but it isn't initialized
 
 error[E0382]: assign of moved value: `d`
-  --> $DIR/issue-21232-partial-init-and-erroneous-use.rs:41:5
+  --> $DIR/issue-21232-partial-init-and-erroneous-use.rs:39:5
    |
 LL |     let mut d = D { x: 0, s: S{ y: 0, z: 0 } };
    |         ----- move occurs because `d` has type `D`, which does not implement the `Copy` trait
@@ -20,20 +24,28 @@ LL |     drop(d);
 LL |     d.x = 10;
    |     ^^^^^^^^ value assigned here after move
 
-error[E0381]: assign to part of possibly-uninitialized variable: `d`
+error[E0381]: binding `d.s` isn't fully initialized
-  --> $DIR/issue-21232-partial-init-and-erroneous-use.rs:47:5
+  --> $DIR/issue-21232-partial-init-and-erroneous-use.rs:45:5
    |
+LL |     let d: D;
+   |         - variable declared here
 LL |     d.s.y = 20;
-   |     ^^^^^^^^^^ use of possibly-uninitialized `d.s`
+   |     ^^^^^^^^^^ `d.s` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `d`
+error[E0381]: binding `d.s` isn't fully initialized
-  --> $DIR/issue-21232-partial-init-and-erroneous-use.rs:53:5
+  --> $DIR/issue-21232-partial-init-and-erroneous-use.rs:50:5
    |
+LL |     let mut d: D;
+   |         ----- variable declared here
 LL |     d.s.y = 20;
-   |     ^^^^^^^^^^ use of possibly-uninitialized `d.s`
+   |     ^^^^^^^^^^ `d.s` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error[E0382]: assign to part of moved value: `d`
-  --> $DIR/issue-21232-partial-init-and-erroneous-use.rs:60:5
+  --> $DIR/issue-21232-partial-init-and-erroneous-use.rs:56:5
    |
 LL |     let mut d = D { x: 0, s: S{ y: 0, z: 0} };
    |         ----- move occurs because `d` has type `D`, which does not implement the `Copy` trait

src/test/ui/nll/issue-21232-partial-init-and-use.rs

@@ -94,15 +94,13 @@ macro_rules! use_part {
 
 fn test_0000_local_fully_init_and_use_struct() {
     let s: S<B>;
-    s.x = 10; s.y = Box::new(20);
+    s.x = 10; s.y = Box::new(20); //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `s` [E0381]
     use_fully!(struct s);
 }
 
 fn test_0001_local_fully_init_and_use_tuple() {
     let t: T;
-    t.0 = 10; t.1 = Box::new(20);
+    t.0 = 10; t.1 = Box::new(20); //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `t` [E0381]
     use_fully!(tuple t);
 }
 
@@ -122,15 +120,13 @@ fn test_0011_local_fully_reinit_and_use_tuple() {
 
 fn test_0100_local_partial_init_and_use_struct() {
     let s: S<B>;
-    s.x = 10;
+    s.x = 10; //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `s` [E0381]
     use_part!(struct s);
 }
 
 fn test_0101_local_partial_init_and_use_tuple() {
     let t: T;
-    t.0 = 10;
+    t.0 = 10; //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `t` [E0381]
     use_part!(tuple t);
 }
 
@@ -150,15 +146,13 @@ fn test_0111_local_partial_reinit_and_use_tuple() {
 
 fn test_0200_local_void_init_and_use_struct() {
     let s: S<Void>;
-    s.x = 10;
+    s.x = 10; //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `s` [E0381]
     use_part!(struct s);
 }
 
 fn test_0201_local_void_init_and_use_tuple() {
     let t: Tvoid;
-    t.0 = 10;
+    t.0 = 10; //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `t` [E0381]
     use_part!(tuple t);
 }
 
@@ -173,15 +167,13 @@ fn test_0201_local_void_init_and_use_tuple() {
 
 fn test_1000_field_fully_init_and_use_struct() {
     let q: Q<S<B>>;
-    q.r.f.x = 10; q.r.f.y = Box::new(20);
+    q.r.f.x = 10; q.r.f.y = Box::new(20); //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `q` [E0381]
     use_fully!(struct q.r.f);
 }
 
 fn test_1001_field_fully_init_and_use_tuple() {
     let q: Q<T>;
-    q.r.f.0 = 10; q.r.f.1 = Box::new(20);
+    q.r.f.0 = 10; q.r.f.1 = Box::new(20); //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `q` [E0381]
     use_fully!(tuple q.r.f);
 }
 
@@ -201,15 +193,13 @@ fn test_1011_field_fully_reinit_and_use_tuple() {
 
 fn test_1100_field_partial_init_and_use_struct() {
     let q: Q<S<B>>;
-    q.r.f.x = 10;
+    q.r.f.x = 10; //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `q` [E0381]
     use_part!(struct q.r.f);
 }
 
 fn test_1101_field_partial_init_and_use_tuple() {
     let q: Q<T>;
-    q.r.f.0 = 10;
+    q.r.f.0 = 10; //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `q` [E0381]
     use_part!(tuple q.r.f);
 }
 
@@ -229,15 +219,13 @@ fn test_1111_field_partial_reinit_and_use_tuple() {
 
 fn test_1200_field_void_init_and_use_struct() {
     let mut q: Q<S<Void>>;
-    q.r.f.x = 10;
+    q.r.f.x = 10; //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `q` [E0381]
     use_part!(struct q.r.f);
 }
 
 fn test_1201_field_void_init_and_use_tuple() {
     let mut q: Q<Tvoid>;
-    q.r.f.0 = 10;
+    q.r.f.0 = 10; //~ ERROR E0381
-    //~^ ERROR assign to part of possibly-uninitialized variable: `q` [E0381]
     use_part!(tuple q.r.f);
 }
 

src/test/ui/nll/issue-21232-partial-init-and-use.stderr

@@ -1,17 +1,25 @@
-error[E0381]: assign to part of possibly-uninitialized variable: `s`
+error[E0381]: binding `s` isn't fully initialized
   --> $DIR/issue-21232-partial-init-and-use.rs:97:5
    |
+LL |     let s: S<B>;
+   |         - variable declared here
 LL |     s.x = 10; s.y = Box::new(20);
-   |     ^^^^^^^^ use of possibly-uninitialized `s`
+   |     ^^^^^^^^ `s` partially assigned here but it isn't fully initialized
-
-error[E0381]: assign to part of possibly-uninitialized variable: `t`
-  --> $DIR/issue-21232-partial-init-and-use.rs:104:5
    |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
+
+error[E0381]: binding `t` isn't fully initialized
+  --> $DIR/issue-21232-partial-init-and-use.rs:103:5
+   |
+LL |     let t: T;
+   |         - variable declared here
 LL |     t.0 = 10; t.1 = Box::new(20);
-   |     ^^^^^^^^ use of possibly-uninitialized `t`
+   |     ^^^^^^^^ `t` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error[E0382]: assign to part of moved value: `s`
-  --> $DIR/issue-21232-partial-init-and-use.rs:111:5
+  --> $DIR/issue-21232-partial-init-and-use.rs:109:5
    |
 LL |     let mut s: S<B> = S::new(); drop(s);
    |         -----                        - value moved here
@@ -21,7 +29,7 @@ LL |     s.x = 10; s.y = Box::new(20);
    |     ^^^^^^^^ value partially assigned here after move
 
 error[E0382]: assign to part of moved value: `t`
-  --> $DIR/issue-21232-partial-init-and-use.rs:118:5
+  --> $DIR/issue-21232-partial-init-and-use.rs:116:5
    |
 LL |     let mut t: T = (0, Box::new(0)); drop(t);
    |         -----                             - value moved here
@@ -30,20 +38,28 @@ LL |     let mut t: T = (0, Box::new(0)); drop(t);
 LL |     t.0 = 10; t.1 = Box::new(20);
    |     ^^^^^^^^ value partially assigned here after move
 
-error[E0381]: assign to part of possibly-uninitialized variable: `s`
+error[E0381]: binding `s` isn't fully initialized
-  --> $DIR/issue-21232-partial-init-and-use.rs:125:5
+  --> $DIR/issue-21232-partial-init-and-use.rs:123:5
    |
+LL |     let s: S<B>;
+   |         - variable declared here
 LL |     s.x = 10;
-   |     ^^^^^^^^ use of possibly-uninitialized `s`
+   |     ^^^^^^^^ `s` partially assigned here but it isn't fully initialized
-
-error[E0381]: assign to part of possibly-uninitialized variable: `t`
-  --> $DIR/issue-21232-partial-init-and-use.rs:132:5
    |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
+
+error[E0381]: binding `t` isn't fully initialized
+  --> $DIR/issue-21232-partial-init-and-use.rs:129:5
+   |
+LL |     let t: T;
+   |         - variable declared here
 LL |     t.0 = 10;
-   |     ^^^^^^^^ use of possibly-uninitialized `t`
+   |     ^^^^^^^^ `t` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error[E0382]: assign to part of moved value: `s`
-  --> $DIR/issue-21232-partial-init-and-use.rs:139:5
+  --> $DIR/issue-21232-partial-init-and-use.rs:135:5
    |
 LL |     let mut s: S<B> = S::new(); drop(s);
    |         -----                        - value moved here
@@ -53,7 +69,7 @@ LL |     s.x = 10;
    |     ^^^^^^^^ value partially assigned here after move
 
 error[E0382]: assign to part of moved value: `t`
-  --> $DIR/issue-21232-partial-init-and-use.rs:146:5
+  --> $DIR/issue-21232-partial-init-and-use.rs:142:5
    |
 LL |     let mut t: T = (0, Box::new(0)); drop(t);
    |         -----                             - value moved here
@@ -62,32 +78,48 @@ LL |     let mut t: T = (0, Box::new(0)); drop(t);
 LL |     t.0 = 10;
    |     ^^^^^^^^ value partially assigned here after move
 
-error[E0381]: assign to part of possibly-uninitialized variable: `s`
+error[E0381]: binding `s` isn't fully initialized
-  --> $DIR/issue-21232-partial-init-and-use.rs:153:5
+  --> $DIR/issue-21232-partial-init-and-use.rs:149:5
    |
+LL |     let s: S<Void>;
+   |         - variable declared here
 LL |     s.x = 10;
-   |     ^^^^^^^^ use of possibly-uninitialized `s`
+   |     ^^^^^^^^ `s` partially assigned here but it isn't fully initialized
-
-error[E0381]: assign to part of possibly-uninitialized variable: `t`
-  --> $DIR/issue-21232-partial-init-and-use.rs:160:5
    |
-LL |     t.0 = 10;
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
-   |     ^^^^^^^^ use of possibly-uninitialized `t`
 
-error[E0381]: assign to part of possibly-uninitialized variable: `q`
+error[E0381]: binding `t` isn't fully initialized
+  --> $DIR/issue-21232-partial-init-and-use.rs:155:5
+   |
+LL |     let t: Tvoid;
+   |         - variable declared here
+LL |     t.0 = 10;
+   |     ^^^^^^^^ `t` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
+
+error[E0381]: binding `q.r.f` isn't fully initialized
+  --> $DIR/issue-21232-partial-init-and-use.rs:170:5
+   |
+LL |     let q: Q<S<B>>;
+   |         - variable declared here
+LL |     q.r.f.x = 10; q.r.f.y = Box::new(20);
+   |     ^^^^^^^^^^^^ `q.r.f` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
+
+error[E0381]: binding `q.r.f` isn't fully initialized
   --> $DIR/issue-21232-partial-init-and-use.rs:176:5
    |
-LL |     q.r.f.x = 10; q.r.f.y = Box::new(20);
+LL |     let q: Q<T>;
-   |     ^^^^^^^^^^^^ use of possibly-uninitialized `q.r.f`
+   |         - variable declared here
-
-error[E0381]: assign to part of possibly-uninitialized variable: `q`
-  --> $DIR/issue-21232-partial-init-and-use.rs:183:5
-   |
 LL |     q.r.f.0 = 10; q.r.f.1 = Box::new(20);
-   |     ^^^^^^^^^^^^ use of possibly-uninitialized `q.r.f`
+   |     ^^^^^^^^^^^^ `q.r.f` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error[E0382]: assign to part of moved value: `q.r`
-  --> $DIR/issue-21232-partial-init-and-use.rs:190:5
+  --> $DIR/issue-21232-partial-init-and-use.rs:182:5
    |
 LL |     let mut q: Q<S<B>> = Q::new(S::new()); drop(q.r);
    |                                                 --- value moved here
@@ -97,7 +129,7 @@ LL |     q.r.f.x = 10; q.r.f.y = Box::new(20);
    = note: move occurs because `q.r` has type `R<S<Box<u32>>>`, which does not implement the `Copy` trait
 
 error[E0382]: assign to part of moved value: `q.r`
-  --> $DIR/issue-21232-partial-init-and-use.rs:197:5
+  --> $DIR/issue-21232-partial-init-and-use.rs:189:5
    |
 LL |     let mut q: Q<T> = Q::new((0, Box::new(0))); drop(q.r);
    |                                                      --- value moved here
@@ -106,20 +138,28 @@ LL |     q.r.f.0 = 10; q.r.f.1 = Box::new(20);
    |
    = note: move occurs because `q.r` has type `R<(u32, Box<u32>)>`, which does not implement the `Copy` trait
 
-error[E0381]: assign to part of possibly-uninitialized variable: `q`
+error[E0381]: binding `q.r.f` isn't fully initialized
-  --> $DIR/issue-21232-partial-init-and-use.rs:204:5
+  --> $DIR/issue-21232-partial-init-and-use.rs:196:5
    |
+LL |     let q: Q<S<B>>;
+   |         - variable declared here
 LL |     q.r.f.x = 10;
-   |     ^^^^^^^^^^^^ use of possibly-uninitialized `q.r.f`
+   |     ^^^^^^^^^^^^ `q.r.f` partially assigned here but it isn't fully initialized
-
-error[E0381]: assign to part of possibly-uninitialized variable: `q`
-  --> $DIR/issue-21232-partial-init-and-use.rs:211:5
    |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
+
+error[E0381]: binding `q.r.f` isn't fully initialized
+  --> $DIR/issue-21232-partial-init-and-use.rs:202:5
+   |
+LL |     let q: Q<T>;
+   |         - variable declared here
 LL |     q.r.f.0 = 10;
-   |     ^^^^^^^^^^^^ use of possibly-uninitialized `q.r.f`
+   |     ^^^^^^^^^^^^ `q.r.f` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error[E0382]: assign to part of moved value: `q.r`
-  --> $DIR/issue-21232-partial-init-and-use.rs:218:5
+  --> $DIR/issue-21232-partial-init-and-use.rs:208:5
    |
 LL |     let mut q: Q<S<B>> = Q::new(S::new()); drop(q.r);
    |                                                 --- value moved here
@@ -129,7 +169,7 @@ LL |     q.r.f.x = 10;
    = note: move occurs because `q.r` has type `R<S<Box<u32>>>`, which does not implement the `Copy` trait
 
 error[E0382]: assign to part of moved value: `q.r`
-  --> $DIR/issue-21232-partial-init-and-use.rs:225:5
+  --> $DIR/issue-21232-partial-init-and-use.rs:215:5
    |
 LL |     let mut q: Q<T> = Q::new((0, Box::new(0))); drop(q.r);
    |                                                      --- value moved here
@@ -138,20 +178,28 @@ LL |     q.r.f.0 = 10;
    |
    = note: move occurs because `q.r` has type `R<(u32, Box<u32>)>`, which does not implement the `Copy` trait
 
-error[E0381]: assign to part of possibly-uninitialized variable: `q`
+error[E0381]: binding `q.r.f` isn't fully initialized
-  --> $DIR/issue-21232-partial-init-and-use.rs:232:5
+  --> $DIR/issue-21232-partial-init-and-use.rs:222:5
    |
+LL |     let mut q: Q<S<Void>>;
+   |         ----- variable declared here
 LL |     q.r.f.x = 10;
-   |     ^^^^^^^^^^^^ use of possibly-uninitialized `q.r.f`
+   |     ^^^^^^^^^^^^ `q.r.f` partially assigned here but it isn't fully initialized
-
-error[E0381]: assign to part of possibly-uninitialized variable: `q`
-  --> $DIR/issue-21232-partial-init-and-use.rs:239:5
    |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
+
+error[E0381]: binding `q.r.f` isn't fully initialized
+  --> $DIR/issue-21232-partial-init-and-use.rs:228:5
+   |
+LL |     let mut q: Q<Tvoid>;
+   |         ----- variable declared here
 LL |     q.r.f.0 = 10;
-   |     ^^^^^^^^^^^^ use of possibly-uninitialized `q.r.f`
+   |     ^^^^^^^^^^^^ `q.r.f` partially assigned here but it isn't fully initialized
+   |
+   = help: partial initialization isn't supported, fully initialize the binding with a default value and mutate, or use `std::mem::MaybeUninit`
 
 error[E0382]: assign to part of moved value: `c`
-  --> $DIR/issue-21232-partial-init-and-use.rs:257:13
+  --> $DIR/issue-21232-partial-init-and-use.rs:245:13
    |
 LL |     let mut c = (1, "".to_owned());
    |         ----- move occurs because `c` has type `(i32, String)`, which does not implement the `Copy` trait
@@ -162,7 +210,7 @@ LL |             c.0 = 2;
    |             ^^^^^^^ value partially assigned here after move
 
 error[E0382]: assign to part of moved value: `c`
-  --> $DIR/issue-21232-partial-init-and-use.rs:267:13
+  --> $DIR/issue-21232-partial-init-and-use.rs:255:13
    |
 LL |     let mut c = (1, (1, "".to_owned()));
    |         ----- move occurs because `c` has type `(i32, (i32, String))`, which does not implement the `Copy` trait
@@ -173,7 +221,7 @@ LL |             (c.1).0 = 2;
    |             ^^^^^^^^^^^ value partially assigned here after move
 
 error[E0382]: assign to part of moved value: `c.1`
-  --> $DIR/issue-21232-partial-init-and-use.rs:275:13
+  --> $DIR/issue-21232-partial-init-and-use.rs:263:13
    |
 LL |         c2 => {
    |         -- value moved here

src/test/ui/nll/match-cfg-fake-edges.rs

@@ -18,7 +18,7 @@ fn guard_may_be_skipped(y: i32) {
     match y {
         _ if { x = 2; true } => 1,
         _ if {
-            x; //~ ERROR use of possibly-uninitialized variable: `x`
+            x; //~ ERROR E0381
             false
         } => 2,
         _ => 3,

src/test/ui/nll/match-cfg-fake-edges.stderr

@@ -1,8 +1,13 @@
-error[E0381]: use of possibly-uninitialized variable: `x`
+error[E0381]: binding `x` isn't initialized in all conditions
   --> $DIR/match-cfg-fake-edges.rs:21:13
    |
+LL |     let x;
+   |         - variable declared here
+...
+LL |         _ if {
+   |         - `x` is uninitialized if this pattern is matched
 LL |             x;
-   |             ^ use of possibly-uninitialized `x`
+   |             ^ `x` used here but it isn't initialized in all conditions
 
 error[E0382]: use of moved value: `x`
   --> $DIR/match-cfg-fake-edges.rs:35:13

src/test/ui/nll/match-on-borrowed.stderr

@@ -33,11 +33,13 @@ LL |     match t {
 LL |     x;
    |     - borrow later used here
 
-error[E0381]: use of possibly-uninitialized variable: `n`
+error[E0381]: binding `n` isn't initialized
   --> $DIR/match-on-borrowed.rs:93:11
    |
+LL |     let n: Never;
+   |         - variable declared here
 LL |     match n {}
-   |           ^ use of possibly-uninitialized `n`
+   |           ^ `n` used here but it isn't initialized
 
 error: aborting due to 4 previous errors