Rollup merge of #117382 - gurry:114529-ice-const-eval, r=oli-obk

Fail typeck for illegal break-with-value

This is fixes the issue wherein typeck was succeeding for break-with-value exprs at illegal locations such as inside `while`, `while let` and `for` loops which eventually caused an ICE during MIR interpretation for const eval.

Now we fail typeck for such code which prevents faulty MIR from being generated and interpreted, thus fixing the ICE.

Fixes #114529

compiler/rustc_hir_typeck/src/expr.rs

@@ -625,10 +625,15 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     }
                 };
 
-                // If the loop context is not a `loop { }`, then break with
-                // a value is illegal, and `opt_coerce_to` will be `None`.
-                // Just set expectation to error in that case.
-                let coerce_to = opt_coerce_to.unwrap_or_else(|| Ty::new_misc_error(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);
+                    }
+                };
 
                 // 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

@@ -0,0 +1,20 @@
+// Regression test for issue #114529
+// Tests that we do not ICE during const eval for a
+// break-with-value in contexts where it is illegal
+
+#[allow(while_true)]
+fn main() {
+    [(); {
+        while true {
+            break 9; //~ ERROR `break` with value from a `while` loop
+        };
+        51
+    }];
+
+    [(); {
+        while let Some(v) = Some(9) {
+            break v; //~ ERROR `break` with value from a `while` loop
+        };
+        51
+    }];
+}

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

@@ -0,0 +1,29 @@
+error[E0571]: `break` with value from a `while` loop
+  --> $DIR/issue-114529-illegal-break-with-value.rs:9:13
+   |
+LL |         while true {
+   |         ---------- you can't `break` with a value in a `while` loop
+LL |             break 9;
+   |             ^^^^^^^ 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[E0571]: `break` with value from a `while` loop
+  --> $DIR/issue-114529-illegal-break-with-value.rs:16:13
+   |
+LL |         while let Some(v) = Some(9) {
+   |         --------------------------- you can't `break` with a value in a `while` loop
+LL |             break v;
+   |             ^^^^^^^ 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 2 previous errors
+
+For more information about this error, try `rustc --explain E0571`.