Auto merge of #108504 - cjgillot:thir-pattern, r=compiler-errors,Nilstrieb

Check pattern refutability on THIR

The current `check_match` query is based on HIR, but partially re-lowers HIR into THIR.
This PR proposed to use the results of the `thir_body` query to check matches, instead of re-building THIR.

Most of the diagnostic changes are spans getting shorter, or commas/semicolons not getting removed.

This PR degrades the diagnostic for confusing constants in patterns (`let A = foo()` where `A` resolves to a `const A` somewhere): it does not point ot the definition of `const A` any more.

compiler/rustc_middle/src/dep_graph/mod.rs

@@ -94,7 +94,7 @@ impl<'tcx> DepContext for TyCtxt<'tcx> {
     }
 
     #[inline]
-    fn dep_kind_info(&self, dep_kind: DepKind) -> &DepKindStruct<'tcx> {
-        &self.query_kinds[dep_kind as usize]
+    fn dep_kind_info(&self, dk: DepKind) -> &DepKindStruct<'tcx> {
+        &self.query_kinds[dk as usize]
     }
 }

compiler/rustc_middle/src/mir/mod.rs

@@ -2001,6 +2001,13 @@ impl<'tcx> Rvalue<'tcx> {
 }
 
 impl BorrowKind {
+    pub fn mutability(&self) -> Mutability {
+        match *self {
+            BorrowKind::Shared | BorrowKind::Shallow | BorrowKind::Unique => Mutability::Not,
+            BorrowKind::Mut { .. } => Mutability::Mut,
+        }
+    }
+
     pub fn allows_two_phase_borrow(&self) -> bool {
         match *self {
             BorrowKind::Shared | BorrowKind::Shallow | BorrowKind::Unique => false,

compiler/rustc_middle/src/query/mod.rs

@@ -1114,9 +1114,9 @@ rustc_queries! {
         desc { "converting literal to mir constant" }
     }
 
-    query check_match(key: DefId) {
-        desc { |tcx| "match-checking `{}`", tcx.def_path_str(key) }
-        cache_on_disk_if { key.is_local() }
+    query check_match(key: LocalDefId) {
+        desc { |tcx| "match-checking `{}`", tcx.def_path_str(key.to_def_id()) }
+        cache_on_disk_if { true }
     }
 
     /// Performs part of the privacy check and computes effective visibilities.

compiler/rustc_middle/src/thir.rs

@@ -227,6 +227,9 @@ pub enum StmtKind<'tcx> {
 
         /// The lint level for this `let` statement.
         lint_level: LintLevel,
+
+        /// Span of the `let <PAT> = <INIT>` part.
+        span: Span,
     },
 }
 
@@ -594,6 +597,55 @@ impl<'tcx> Pat<'tcx> {
             _ => None,
         }
     }
+
+    /// Call `f` on every "binding" in a pattern, e.g., on `a` in
+    /// `match foo() { Some(a) => (), None => () }`
+    pub fn each_binding(&self, mut f: impl FnMut(Symbol, BindingMode, Ty<'tcx>, Span)) {
+        self.walk_always(|p| {
+            if let PatKind::Binding { name, mode, ty, .. } = p.kind {
+                f(name, mode, ty, p.span);
+            }
+        });
+    }
+
+    /// Walk the pattern in left-to-right order.
+    ///
+    /// If `it(pat)` returns `false`, the children are not visited.
+    pub fn walk(&self, mut it: impl FnMut(&Pat<'tcx>) -> bool) {
+        self.walk_(&mut it)
+    }
+
+    fn walk_(&self, it: &mut impl FnMut(&Pat<'tcx>) -> bool) {
+        if !it(self) {
+            return;
+        }
+
+        use PatKind::*;
+        match &self.kind {
+            Wild | Range(..) | Binding { subpattern: None, .. } | Constant { .. } => {}
+            AscribeUserType { subpattern, .. }
+            | Binding { subpattern: Some(subpattern), .. }
+            | Deref { subpattern } => subpattern.walk_(it),
+            Leaf { subpatterns } | Variant { subpatterns, .. } => {
+                subpatterns.iter().for_each(|field| field.pattern.walk_(it))
+            }
+            Or { pats } => pats.iter().for_each(|p| p.walk_(it)),
+            Array { box ref prefix, ref slice, box ref suffix }
+            | Slice { box ref prefix, ref slice, box ref suffix } => {
+                prefix.iter().chain(slice.iter()).chain(suffix.iter()).for_each(|p| p.walk_(it))
+            }
+        }
+    }
+
+    /// Walk the pattern in left-to-right order.
+    ///
+    /// If you always want to recurse, prefer this method over `walk`.
+    pub fn walk_always(&self, mut it: impl FnMut(&Pat<'tcx>)) {
+        self.walk(|p| {
+            it(p);
+            true
+        })
+    }
 }
 
 impl<'tcx> IntoDiagnosticArg for Pat<'tcx> {
@@ -879,7 +931,7 @@ mod size_asserts {
     static_assert_size!(ExprKind<'_>, 40);
     static_assert_size!(Pat<'_>, 72);
     static_assert_size!(PatKind<'_>, 56);
-    static_assert_size!(Stmt<'_>, 48);
-    static_assert_size!(StmtKind<'_>, 40);
+    static_assert_size!(Stmt<'_>, 56);
+    static_assert_size!(StmtKind<'_>, 48);
     // tidy-alphabetical-end
 }

compiler/rustc_middle/src/thir/visit.rs

@@ -175,6 +175,7 @@ pub fn walk_stmt<'a, 'tcx: 'a, V: Visitor<'a, 'tcx>>(visitor: &mut V, stmt: &Stm
             ref pattern,
             lint_level: _,
             else_block,
+            span: _,
         } => {
             if let Some(init) = initializer {
                 visitor.visit_expr(&visitor.thir()[*init]);