Auto merge of #55162 - nikomatsakis:issue-54902-underscore-bound, r=tmandry

handle underscore bounds in unexpected places

Per the discussion on #54902, I made it a hard error to use lifetime bounds in various places where they used to be permitted:

- `where Foo: Bar<'_>` for example

I also moved error reporting to HIR lowering and added `Error` variants to let us suppress downstream errors that result.

I (imo) improved the error message wording to be clearer, as well.

In the process, I fixed the ICE in #52098.

Fixes #54902
Fixes #52098

2 files changed, 9 insertions, 9 deletions

diff --git a/src/test/ui/error-codes/E0637.rs b/src/test/ui/error-codes/E0637.rs
index ee6a978d169..b4f769a749f 100644
--- a/src/test/ui/error-codes/E0637.rs
+++ b/src/test/ui/error-codes/E0637.rs
@@ -8,11 +8,11 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-struct Foo<'a: '_>(&'a u8); //~ ERROR invalid lifetime bound name: `'_`
-fn foo<'a: '_>(_: &'a u8) {} //~ ERROR invalid lifetime bound name: `'_`
+struct Foo<'a: '_>(&'a u8); //~ ERROR cannot be used here
+fn foo<'a: '_>(_: &'a u8) {} //~ ERROR cannot be used here
 
 struct Bar<'a>(&'a u8);
-impl<'a: '_> Bar<'a> { //~ ERROR invalid lifetime bound name: `'_`
+impl<'a: '_> Bar<'a> { //~ ERROR cannot be used here
   fn bar() {}
 }
 
diff --git a/src/test/ui/error-codes/E0637.stderr b/src/test/ui/error-codes/E0637.stderr
index 245729376df..2a4545fc43d 100644
--- a/src/test/ui/error-codes/E0637.stderr
+++ b/src/test/ui/error-codes/E0637.stderr
@@ -1,19 +1,19 @@
-error[E0637]: invalid lifetime bound name: `'_`
+error[E0637]: `'_` cannot be used here
   --> $DIR/E0637.rs:11:16
    |
-LL | struct Foo<'a: '_>(&'a u8); //~ ERROR invalid lifetime bound name: `'_`
+LL | struct Foo<'a: '_>(&'a u8); //~ ERROR cannot be used here
    |                ^^ `'_` is a reserved lifetime name
 
-error[E0637]: invalid lifetime bound name: `'_`
+error[E0637]: `'_` cannot be used here
   --> $DIR/E0637.rs:12:12
    |
-LL | fn foo<'a: '_>(_: &'a u8) {} //~ ERROR invalid lifetime bound name: `'_`
+LL | fn foo<'a: '_>(_: &'a u8) {} //~ ERROR cannot be used here
    |            ^^ `'_` is a reserved lifetime name
 
-error[E0637]: invalid lifetime bound name: `'_`
+error[E0637]: `'_` cannot be used here
   --> $DIR/E0637.rs:15:10
    |
-LL | impl<'a: '_> Bar<'a> { //~ ERROR invalid lifetime bound name: `'_`
+LL | impl<'a: '_> Bar<'a> { //~ ERROR cannot be used here
    |          ^^ `'_` is a reserved lifetime name
 
 error: aborting due to 3 previous errors