Auto merge of #52568 - oli-obk:span_bug_error, r=varkor

Fix loop label resolution around constants

And make `delay_span_bug` a little more helpful

r? @varkor

fixes #52442
fixes #52443

src/test/ui/const-eval/issue-52442.rs

@@ -0,0 +1,13 @@
+// Copyright 2018 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 main() {
+    [();  { &loop { break } as *const _ as usize } ]; //~ ERROR unimplemented expression type
+}

src/test/ui/const-eval/issue-52442.stderr

@@ -0,0 +1,9 @@
+error[E0019]: constant contains unimplemented expression type
+  --> $DIR/issue-52442.rs:12:14
+   |
+LL |     [();  { &loop { break } as *const _ as usize } ]; //~ ERROR unimplemented expression type
+   |              ^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0019`.

src/test/ui/const-eval/issue-52443.rs

@@ -0,0 +1,18 @@
+// Copyright 2018 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 main() {
+    [(); & { loop { continue } } ]; //~ ERROR mismatched types
+    [(); loop { break }]; //~ ERROR mismatched types
+    [(); {while true {break}; 0}]; //~ ERROR constant contains unimplemented expression type
+    [(); { for _ in 0usize.. {}; 0}]; //~ ERROR calls in constants are limited to constant functions
+    //~^ ERROR constant contains unimplemented expression type
+    //~| ERROR could not evaluate repeat length
+}

src/test/ui/const-eval/issue-52443.stderr

@@ -0,0 +1,51 @@
+error[E0308]: mismatched types
+  --> $DIR/issue-52443.rs:12:10
+   |
+LL |     [(); & { loop { continue } } ]; //~ ERROR mismatched types
+   |          ^^^^^^^^^^^^^^^^^^^^^^^
+   |          |
+   |          expected usize, found reference
+   |          help: consider removing the borrow: `{ loop { continue } }`
+   |
+   = note: expected type `usize`
+              found type `&_`
+
+error[E0308]: mismatched types
+  --> $DIR/issue-52443.rs:13:17
+   |
+LL |     [(); loop { break }]; //~ ERROR mismatched types
+   |                 ^^^^^ expected (), found usize
+   |
+   = note: expected type `()`
+              found type `usize`
+
+error[E0019]: constant contains unimplemented expression type
+  --> $DIR/issue-52443.rs:14:11
+   |
+LL |     [(); {while true {break}; 0}]; //~ ERROR constant contains unimplemented expression type
+   |           ^^^^^^^^^^^^^^^^^^
+
+error[E0015]: calls in constants are limited to constant functions, tuple structs and tuple variants
+  --> $DIR/issue-52443.rs:15:21
+   |
+LL |     [(); { for _ in 0usize.. {}; 0}]; //~ ERROR calls in constants are limited to constant functions
+   |                     ^^^^^^^^
+
+error[E0019]: constant contains unimplemented expression type
+  --> $DIR/issue-52443.rs:15:21
+   |
+LL |     [(); { for _ in 0usize.. {}; 0}]; //~ ERROR calls in constants are limited to constant functions
+   |                     ^^^^^^^^
+
+error[E0080]: could not evaluate repeat length
+  --> $DIR/issue-52443.rs:15:10
+   |
+LL |     [(); { for _ in 0usize.. {}; 0}]; //~ ERROR calls in constants are limited to constant functions
+   |          ^^^^^^^^^^^--------^^^^^^^
+   |                     |
+   |                     calling non-const fn `<I as std::iter::IntoIterator><std::ops::RangeFrom<usize>>::into_iter`
+
+error: aborting due to 6 previous errors
+
+Some errors occurred: E0015, E0019, E0080, E0308.
+For more information about an error, try `rustc --explain E0015`.