Type-check break value; even outside of loop {}.

Fix rust-lang#43162, fix rust-lang#43727.

Author: kennytm

src/librustc_typeck/check/mod.rs

@@ -3652,6 +3652,20 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
                   // inside a loop at all, which is caught by the
                   // loop-checking pass.
                   assert!(self.tcx.sess.err_count() > 0);
+
+                  // We still need to assign a type to the inner expression to
+                  // prevent the ICE in #43162.
+                  if let Some(ref e) = *expr_opt {
+                      self.check_expr_with_hint(e, tcx.types.err);
+
+                      // ... except when we try to 'break rust;'.
+                      // ICE this expression in particular (see #43162).
+                      if let hir::ExprPath(hir::QPath::Resolved(_, ref path)) = e.node {
+                          if path.segments.len() == 1 && path.segments[0].name == "rust" {
+                              fatally_break_rust(self.tcx.sess);
+                          }
+                      }
+                  }
               }
 
               // the type of a `break` is always `!`, since it diverges
@@ -4857,3 +4871,20 @@ pub fn check_bounds_are_used<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
         }
     }
 }
+
+fn fatally_break_rust(sess: &Session) {
+    let handler = sess.diagnostic();
+    handler.span_bug_no_panic(
+        MultiSpan::new(),
+        "It looks like you're trying to break rust; would you like some ICE?",
+    );
+    handler.note_without_error("the compiler expectedly panicked. this is a feature.");
+    handler.note_without_error(
+        "we would appreciate a joke overview: \
+        https://github.com/rust-lang/rust/issues/43162#issuecomment-320764675"
+    );
+    handler.note_without_error(&format!("rustc {} running on {}",
+        option_env!("CFG_VERSION").unwrap_or("unknown_version"),
+        ::session::config::host_triple(),
+    ));
+}

src/test/compile-fail/issue-43162.rs

@@ -0,0 +1,17 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+fn foo() -> bool {
+    break true; //~ ERROR E0268
+}
+
+fn main() {
+    break {}; //~ ERROR E0268
+}

src/test/run-pass/loop-break-value.rs

@@ -137,4 +137,10 @@ pub fn main() {
         panic!("from outer");
     };
     assert_eq!(break_from_while_to_outer, 567);
+
+    let rust = true;
+    let value = loop {
+        break rust;
+    };
+    assert!(value);
 }