diff --git a/compiler/rustc_typeck/src/check/expr.rs b/compiler/rustc_typeck/src/check/expr.rs index 9990f86a36b13..dce3be9399dd6 100644 --- a/compiler/rustc_typeck/src/check/expr.rs +++ b/compiler/rustc_typeck/src/check/expr.rs @@ -627,7 +627,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> { 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 |= !self.diverges.get().is_always(); // 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 index 0000000000000..d070fddaffc19 --- /dev/null +++ b/src/test/ui/break-diverging-value.rs @@ -0,0 +1,37 @@ +#![feature(never_type)] + +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 loop_break_return_2() -> i32 { + let loop_value = loop { break { return 0; () } }; // ok +} + +enum Void {} + +fn get_void() -> Void { + panic!() +} + +fn loop_break_void() -> i32 { //~ ERROR mismatched types + let loop_value = loop { break get_void() }; +} + +fn get_never() -> ! { + panic!() +} + +fn loop_break_never() -> i32 { + let loop_value = loop { break get_never() }; // ok +} + +fn main() {} diff --git a/src/test/ui/break-diverging-value.stderr b/src/test/ui/break-diverging-value.stderr new file mode 100644 index 0000000000000..69edcd2408002 --- /dev/null +++ b/src/test/ui/break-diverging-value.stderr @@ -0,0 +1,19 @@ +error[E0308]: mismatched types + --> $DIR/break-diverging-value.rs:11:26 + | +LL | fn loop_break_break() -> i32 { + | ---------------- ^^^ expected `i32`, found `()` + | | + | implicitly returns `()` as its body has no tail or `return` expression + +error[E0308]: mismatched types + --> $DIR/break-diverging-value.rs:25:25 + | +LL | fn loop_break_void() -> i32 { + | --------------- ^^^ expected `i32`, found `()` + | | + | implicitly returns `()` as its body has no tail or `return` expression + +error: aborting due to 2 previous errors + +For more information about this error, try `rustc --explain E0308`.