Rollup merge of rust-lang#88451 - theo-lw:issue-87771, r=jackh726

Fix an ICE caused by type mismatch errors being ignored

This PR fixes rust-lang#87771. It turns out that the check on `compiler/rustc_typeck/src/check/demand.rs:148` leads to the ICE. I removed it because the early return in [`check_expr_assign`](https://github.com/theo-lw/rust/blob/dec7fc3ced5bc3c18d0e5d29921d087f93189cb8/compiler/rustc_typeck/src/check/expr.rs#L928) already prevents unnecessary error messages from the call to `check_expr_coercable_to_type`.

compiler/rustc_typeck/src/check/coercion.rs

@@ -1484,21 +1484,7 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
                     fcx.emit_coerce_suggestions(&mut err, expr, found, expected, None);
                 }
 
-                // Error possibly reported in `check_assign` so avoid emitting error again.
-                let assign_to_bool = expression
-                    // #67273: Use initial expected type as opposed to `expected`.
-                    // Otherwise we end up using prior coercions in e.g. a `match` expression:
-                    // ```
-                    // match i {
-                    //     0 => true, // Because of this...
-                    //     1 => i = 1, // ...`expected == bool` now, but not when checking `i = 1`.
-                    //     _ => (),
-                    // };
-                    // ```
-                    .filter(|e| fcx.is_assign_to_bool(e, self.expected_ty()))
-                    .is_some();
-
-                err.emit_unless(assign_to_bool || unsized_return);
+                err.emit_unless(unsized_return);
 
                 self.final_ty = Some(fcx.tcx.ty_error());
             }

compiler/rustc_typeck/src/check/demand.rs

@@ -145,12 +145,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let expr_ty = self.resolve_vars_with_obligations(checked_ty);
         let mut err = self.report_mismatched_types(&cause, expected, expr_ty, e);
 
-        if self.is_assign_to_bool(expr, expected) {
-            // Error reported in `check_assign` so avoid emitting error again.
-            err.delay_as_bug();
-            return (expected, None);
-        }
-
         self.emit_coerce_suggestions(&mut err, expr, expr_ty, expected, expected_ty_expr);
 
         (expected, Some(err))
@@ -172,14 +166,6 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
-    /// Returns whether the expected type is `bool` and the expression is `x = y`.
-    pub fn is_assign_to_bool(&self, expr: &hir::Expr<'_>, expected: Ty<'tcx>) -> bool {
-        if let hir::ExprKind::Assign(..) = expr.kind {
-            return expected == self.tcx.types.bool;
-        }
-        false
-    }
-
     /// If the expected type is an enum (Issue #55250) with any variants whose
     /// sole field is of the found type, suggest such variants. (Issue #42764)
     fn suggest_compatible_variants(

compiler/rustc_typeck/src/check/expr.rs

@@ -92,8 +92,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let expr = expr.peel_drop_temps();
             self.suggest_deref_ref_or_into(&mut err, expr, expected_ty, ty, None);
             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));
+            err.emit();
         }
         ty
     }

src/test/ui/typeck/issue-87771-ice-assign-assign-to-bool.rs

@@ -0,0 +1,4 @@
+fn main() {
+    let mut a;
+    a = a = true; //~ ERROR mismatched types
+}

src/test/ui/typeck/issue-87771-ice-assign-assign-to-bool.stderr

@@ -0,0 +1,9 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-87771-ice-assign-assign-to-bool.rs:3:9
+   |
+LL |     a = a = true;
+   |         ^^^^^^^^ expected `bool`, found `()`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.