Fix control flow check for breaking with diverging values

diff --git a/compiler/rustc_typeck/src/check/expr.rs b/compiler/rustc_typeck/src/check/expr.rs
index 9990f86a36b1374e97b1eb046ffd44e18f2bc538..15820d367c0a669c7998c2c571f45b9db9c85195 100644 (file)
--- a/compiler/rustc_typeck/src/check/expr.rs
+++ b/compiler/rustc_typeck/src/check/expr.rs
@@ -627,7 +627,10 @@ fn check_expr_break(
                 assert!(expr_opt.is_none() || self.tcx.sess.has_errors());
             }
 
-            ctxt.may_break = true;
+            // If we encountered a `break`, then (no surprise) it may be possible to break from the
+            // loop... unless the value being returned from the loop diverges itself, e.g.
+            // `break return 5` or `break loop {}`.
+            ctxt.may_break |= !e_ty.is_never();
 
             // the type of a `break` is always `!`, since it diverges
             tcx.types.never

diff --git a/src/test/ui/break-diverging-value.rs b/src/test/ui/break-diverging-value.rs
new file mode 100644 (file)
index 0000000..0498580
--- /dev/null
+++ b/src/test/ui/break-diverging-value.rs
@@ -0,0 +1,13 @@
+fn loop_break_return() -> i32 {
+    let loop_value = loop { break return 0 }; // ok
+}
+
+fn loop_break_loop() -> i32 {
+    let loop_value = loop { break loop {} }; // ok
+}
+
+fn loop_break_break() -> i32 { //~ ERROR mismatched types
+    let loop_value = loop { break break };
+}
+
+fn main() {}

diff --git a/src/test/ui/break-diverging-value.stderr b/src/test/ui/break-diverging-value.stderr
new file mode 100644 (file)
index 0000000..78a8d78
--- /dev/null
+++ b/src/test/ui/break-diverging-value.stderr
@@ -0,0 +1,11 @@
+error[E0308]: mismatched types
+  --> $DIR/break-diverging-value.rs:9:26
+   |
+LL | fn loop_break_break() -> i32 {
+   |    ----------------      ^^^ expected `i32`, found `()`
+   |    |
+   |    implicitly returns `()` as its body has no tail or `return` expression
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.