Rollup merge of #65213 - estebank:peel-drop-temps, r=Centril

Ignore `ExprKind::DropTemps` for some ref suggestions

Introduce `Expr::peel_drop_temps()` to ignore `ExprKind::DropTemps` for suggestions that depend on the `ExprKind` for accuracy.

src/librustc/hir/mod.rs

@@ -1548,6 +1548,19 @@ impl Expr {
             }
         }
     }
+
+    /// If `Self.kind` is `ExprKind::DropTemps(expr)`, drill down until we get a non-`DropTemps`
+    /// `Expr`. This is used in suggestions to ignore this `ExprKind` as it is semantically
+    /// silent, only signaling the ownership system. By doing this, suggestions that check the
+    /// `ExprKind` of any given `Expr` for presentation don't have to care about `DropTemps`
+    /// beyond remembering to call this function before doing analysis on it.
+    pub fn peel_drop_temps(&self) -> &Self {
+        let mut expr = self;
+        while let ExprKind::DropTemps(inner) = &expr.kind {
+            expr = inner;
+        }
+        expr
+    }
 }
 
 impl fmt::Debug for Expr {

src/librustc_typeck/check/demand.rs

@@ -115,6 +115,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             Err(e) => e
         };
 
+        let expr = expr.peel_drop_temps();
         let cause = self.misc(expr.span);
         let expr_ty = self.resolve_type_vars_with_obligations(checked_ty);
         let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
@@ -355,6 +356,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         };
         let is_macro = sp.from_expansion() && !is_desugaring;
 
+        // `ExprKind::DropTemps` is semantically irrelevant for these suggestions.
+        let expr = expr.peel_drop_temps();
+
         match (&expr.kind, &expected.kind, &checked_ty.kind) {
             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.kind, &check.kind) {
                 (&ty::Str, &ty::Array(arr, _)) |

src/librustc_typeck/check/expr.rs

@@ -87,12 +87,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
 
         if let Some(mut err) = self.demand_suptype_diag(expr.span, expected_ty, ty) {
+            let expr = expr.peel_drop_temps();
             self.suggest_ref_or_into(&mut err, expr, expected_ty, ty);
-
-            let expr = match &expr.kind {
-                ExprKind::DropTemps(expr) => expr,
-                _ => expr,
-            };
             extend_err(&mut err);
             // Error possibly reported in `check_assign` so avoid emitting error again.
             err.emit_unless(self.is_assign_to_bool(expr, expected_ty));

src/librustc_typeck/check/mod.rs

@@ -4216,20 +4216,21 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     pub fn suggest_mismatched_types_on_tail(
         &self,
         err: &mut DiagnosticBuilder<'tcx>,
-        expression: &'tcx hir::Expr,
+        expr: &'tcx hir::Expr,
         expected: Ty<'tcx>,
         found: Ty<'tcx>,
         cause_span: Span,
         blk_id: hir::HirId,
     ) -> bool {
-        self.suggest_missing_semicolon(err, expression, expected, cause_span);
+        let expr = expr.peel_drop_temps();
+        self.suggest_missing_semicolon(err, expr, expected, cause_span);
         let mut pointing_at_return_type = false;
         if let Some((fn_decl, can_suggest)) = self.get_fn_decl(blk_id) {
             pointing_at_return_type = self.suggest_missing_return_type(
                 err, &fn_decl, expected, found, can_suggest);
         }
-        self.suggest_ref_or_into(err, expression, expected, found);
-        self.suggest_boxing_when_appropriate(err, expression, expected, found);
+        self.suggest_ref_or_into(err, expr, expected, found);
+        self.suggest_boxing_when_appropriate(err, expr, expected, found);
         pointing_at_return_type
     }
 

src/test/ui/if/if-no-match-bindings.stderr

@@ -29,7 +29,7 @@ LL |     if &true {}
    |        ^^^^^
    |        |
    |        expected bool, found &bool
-   |        help: consider dereferencing the borrow: `*&true`
+   |        help: consider removing the borrow: `true`
    |
    = note: expected type `bool`
               found type `&bool`
@@ -41,7 +41,7 @@ LL |     if &mut true {}
    |        ^^^^^^^^^
    |        |
    |        expected bool, found &mut bool
-   |        help: consider dereferencing the borrow: `*&mut true`
+   |        help: consider removing the borrow: `true`
    |
    = note: expected type `bool`
               found type `&mut bool`
@@ -77,7 +77,7 @@ LL |     while &true {}
    |           ^^^^^
    |           |
    |           expected bool, found &bool
-   |           help: consider dereferencing the borrow: `*&true`
+   |           help: consider removing the borrow: `true`
    |
    = note: expected type `bool`
               found type `&bool`
@@ -89,7 +89,7 @@ LL |     while &mut true {}
    |           ^^^^^^^^^
    |           |
    |           expected bool, found &mut bool
-   |           help: consider dereferencing the borrow: `*&mut true`
+   |           help: consider removing the borrow: `true`
    |
    = note: expected type `bool`
               found type `&mut bool`

src/test/ui/rfc-2497-if-let-chains/disallowed-positions.stderr

@@ -520,7 +520,7 @@ LL |     if &let 0 = 0 {}
    |        ^^^^^^^^^^
    |        |
    |        expected bool, found &bool
-   |        help: consider dereferencing the borrow: `*&let 0 = 0`
+   |        help: consider removing the borrow: `let 0 = 0`
    |
    = note: expected type `bool`
               found type `&bool`
@@ -708,7 +708,7 @@ LL |     while &let 0 = 0 {}
    |           ^^^^^^^^^^
    |           |
    |           expected bool, found &bool
-   |           help: consider dereferencing the borrow: `*&let 0 = 0`
+   |           help: consider removing the borrow: `let 0 = 0`
    |
    = note: expected type `bool`
               found type `&bool`