Auto merge of #93820 - compiler-errors:gat-wfcheck, r=jackh726

Rework GAT `where` clause check

rework the GAT where check to use a fixed-point algorithm, and check all GATs in a trait at once

fixes #93278

r? `@jackh726`
cc `@nikomatsakis`

2 files changed, 34 insertions, 4 deletions

diff --git a/src/test/ui/generic-associated-types/self-outlives-lint.rs b/src/test/ui/generic-associated-types/self-outlives-lint.rs
index fcc53b4ede0..300907adbfc 100644
--- a/src/test/ui/generic-associated-types/self-outlives-lint.rs
+++ b/src/test/ui/generic-associated-types/self-outlives-lint.rs
@@ -140,11 +140,19 @@ trait NotInReturn {
 // We obviously error for `Iterator`, but we should also error for `Item`
 trait IterableTwo {
     type Item<'a>;
+    //~^ missing required
     type Iterator<'a>: Iterator<Item = Self::Item<'a>>;
     //~^ missing required
     fn iter<'a>(&'a self) -> Self::Iterator<'a>;
 }
 
+trait IterableTwoWhere {
+    type Item<'a>;
+    //~^ missing required
+    type Iterator<'a>: Iterator<Item = Self::Item<'a>> where Self: 'a;
+    fn iter<'a>(&'a self) -> Self::Iterator<'a>;
+}
+
 // We also should report region outlives clauses. Here, we know that `'y: 'x`,
 // because of `&'x &'y`, so we require that `'b: 'a`.
 trait RegionOutlives {
diff --git a/src/test/ui/generic-associated-types/self-outlives-lint.stderr b/src/test/ui/generic-associated-types/self-outlives-lint.stderr
index 3b9146ad875..fdb1f50a776 100644
--- a/src/test/ui/generic-associated-types/self-outlives-lint.stderr
+++ b/src/test/ui/generic-associated-types/self-outlives-lint.stderr
@@ -108,8 +108,19 @@ LL |     type Bar<'b>;
    = note: this bound is currently required to ensure that impls have maximum flexibility
    = note: we are soliciting feedback, see issue #87479 <https://github.com/rust-lang/rust/issues/87479> for more information
 
+error: missing required bound on `Item`
+  --> $DIR/self-outlives-lint.rs:142:5
+   |
+LL |     type Item<'a>;
+   |     ^^^^^^^^^^^^^-
+   |                  |
+   |                  help: add the required where clause: `where Self: 'a`
+   |
+   = note: this bound is currently required to ensure that impls have maximum flexibility
+   = note: we are soliciting feedback, see issue #87479 <https://github.com/rust-lang/rust/issues/87479> for more information
+
 error: missing required bound on `Iterator`
-  --> $DIR/self-outlives-lint.rs:143:5
+  --> $DIR/self-outlives-lint.rs:144:5
    |
 LL |     type Iterator<'a>: Iterator<Item = Self::Item<'a>>;
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^-
@@ -119,8 +130,19 @@ LL |     type Iterator<'a>: Iterator<Item = Self::Item<'a>>;
    = note: this bound is currently required to ensure that impls have maximum flexibility
    = note: we are soliciting feedback, see issue #87479 <https://github.com/rust-lang/rust/issues/87479> for more information
 
+error: missing required bound on `Item`
+  --> $DIR/self-outlives-lint.rs:150:5
+   |
+LL |     type Item<'a>;
+   |     ^^^^^^^^^^^^^-
+   |                  |
+   |                  help: add the required where clause: `where Self: 'a`
+   |
+   = note: this bound is currently required to ensure that impls have maximum flexibility
+   = note: we are soliciting feedback, see issue #87479 <https://github.com/rust-lang/rust/issues/87479> for more information
+
 error: missing required bound on `Bar`
-  --> $DIR/self-outlives-lint.rs:151:5
+  --> $DIR/self-outlives-lint.rs:159:5
    |
 LL |     type Bar<'a, 'b>;
    |     ^^^^^^^^^^^^^^^^-
@@ -131,7 +153,7 @@ LL |     type Bar<'a, 'b>;
    = note: we are soliciting feedback, see issue #87479 <https://github.com/rust-lang/rust/issues/87479> for more information
 
 error: missing required bound on `Fut`
-  --> $DIR/self-outlives-lint.rs:167:5
+  --> $DIR/self-outlives-lint.rs:175:5
    |
 LL |     type Fut<'out>;
    |     ^^^^^^^^^^^^^^-
@@ -141,5 +163,5 @@ LL |     type Fut<'out>;
    = note: this bound is currently required to ensure that impls have maximum flexibility
    = note: we are soliciting feedback, see issue #87479 <https://github.com/rust-lang/rust/issues/87479> for more information
 
-error: aborting due to 13 previous errors
+error: aborting due to 15 previous errors