Auto merge of #45050 - petrochenkov:ambind, r=nikomatsakis

resolve: Use same rules for disambiguating fresh bindings in `match` and `let`

Resolve `Unit` as a unit struct pattern in
```rust
struct Unit;

let Unit = x;
```
consistently with
```rust
match x {
    Unit => {}
}
```
It was previously an error.
(The change also applies to unit variants and constants.)

Fixes https://users.rust-lang.org/t/e0530-cannot-shadow-unit-structs-what-in-the-earthly-what/13054
(This particular change doesn't depend on a fix for the issue mentioned in https://users.rust-lang.org/t/e0530-cannot-shadow-unit-structs-what-in-the-earthly-what/13054/4)

cc @rust-lang/lang
r? @nikomatsakis

1 files changed, 26 insertions, 0 deletions

diff --git a/src/test/ui/const-pattern-irrefutable.rs b/src/test/ui/const-pattern-irrefutable.rs
new file mode 100644
index 00000000000..af0b95e002d
--- /dev/null
+++ b/src/test/ui/const-pattern-irrefutable.rs
@@ -0,0 +1,26 @@
+// Copyright 2015 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.
+
+mod foo {
+    pub const b: u8 = 2;
+    pub const d: u8 = 2;
+}
+
+use foo::b as c;
+use foo::d;
+
+const a: u8 = 2;
+
+fn main() {
+    let a = 4; //~ ERROR refutable pattern in local binding: `_` not covered
+    let c = 4; //~ ERROR refutable pattern in local binding: `_` not covered
+    let d = 4; //~ ERROR refutable pattern in local binding: `_` not covered
+    fn f() {} // Check that the `NOTE`s still work with an item here (c.f. issue #35115).
+}