Typeck break expr even if break is illegal

We were earlier returning immediately when encountering an illegal break. However, this caused problems later
when the expr that the break was returning was evaluated during writeback. So now we don't return and instead
simply set tainted by error. This lets typeck of break expr to occur even though we've encountered an illegal break.

Author: gurry

compiler/rustc_hir_typeck/src/expr.rs

@@ -626,15 +626,18 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     }
                 };
 
-                let coerce_to = match opt_coerce_to {
-                    Some(c) => c,
-                    None => {
-                        // If the loop context is not a `loop { }`, then break with
-                        // a value is illegal, and `opt_coerce_to` will be `None`.
-                        // Return error in that case (#114529).
-                        return Ty::new_misc_error(tcx);
-                    }
-                };
+                // If the loop context is not a `loop { }`, then break with
+                // a value is illegal, and `opt_coerce_to` will be `None`.
+                // Set expectation to error in that case and set tainted
+                // by error (#114529)
+                let coerce_to = opt_coerce_to.unwrap_or_else(|| {
+                    let guar = tcx.sess.delay_span_bug(
+                        expr.span,
+                        "illegal break with value found but no error reported",
+                    );
+                    self.set_tainted_by_errors(guar);
+                    Ty::new_error(tcx, guar)
+                });
 
                 // Recurse without `enclosing_breakables` borrowed.
                 e_ty = self.check_expr_with_hint(e, coerce_to);

tests/ui/typeck/issue-114529-illegal-break-with-value.rs

@@ -17,4 +17,10 @@ fn main() {
         };
         51
     }];
+
+    while true {
+        break (|| { //~ ERROR `break` with value from a `while` loop
+            let local = 9;
+        });
+    }
 }

tests/ui/typeck/issue-114529-illegal-break-with-value.stderr

@@ -24,6 +24,21 @@ help: use `break` on its own without a value inside this `while` loop
 LL |             break;
    |             ~~~~~
 
-error: aborting due to 2 previous errors
+error[E0571]: `break` with value from a `while` loop
+  --> $DIR/issue-114529-illegal-break-with-value.rs:22:9
+   |
+LL |       while true {
+   |       ---------- you can't `break` with a value in a `while` loop
+LL | /         break (|| {
+LL | |             let local = 9;
+LL | |         });
+   | |__________^ can only break with a value inside `loop` or breakable block
+   |
+help: use `break` on its own without a value inside this `while` loop
+   |
+LL |         break;
+   |         ~~~~~
+
+error: aborting due to 3 previous errors
 
 For more information about this error, try `rustc --explain E0571`.