Auto merge of #79209 - spastorino:trait-inheritance-self, r=nikomatsakis

Allow Trait inheritance with cycles on associated types

Fixes #35237

r? `@nikomatsakis`

cc `@estebank`

5 files changed, 22 insertions, 27 deletions

diff --git a/src/test/ui/issues/issue-12511.stderr b/src/test/ui/issues/issue-12511.stderr
index 37e38ff60ae..5f2b98c5237 100644
--- a/src/test/ui/issues/issue-12511.stderr
+++ b/src/test/ui/issues/issue-12511.stderr
@@ -1,15 +1,25 @@
-error[E0391]: cycle detected when computing the supertraits of `T1`
+error[E0391]: cycle detected when computing the super predicates of `T1`
+  --> $DIR/issue-12511.rs:1:1
+   |
+LL | trait T1 : T2 {
+   | ^^^^^^^^^^^^^
+   |
+note: ...which requires computing the super traits of `T1`...
   --> $DIR/issue-12511.rs:1:12
    |
 LL | trait T1 : T2 {
    |            ^^
+note: ...which requires computing the super predicates of `T2`...
+  --> $DIR/issue-12511.rs:5:1
    |
-note: ...which requires computing the supertraits of `T2`...
+LL | trait T2 : T1 {
+   | ^^^^^^^^^^^^^
+note: ...which requires computing the super traits of `T2`...
   --> $DIR/issue-12511.rs:5:12
    |
 LL | trait T2 : T1 {
    |            ^^
-   = note: ...which again requires computing the supertraits of `T1`, completing the cycle
+   = note: ...which again requires computing the super predicates of `T1`, completing the cycle
 note: cycle used when collecting item types in top-level module
   --> $DIR/issue-12511.rs:1:1
    |
diff --git a/src/test/ui/issues/issue-20772.stderr b/src/test/ui/issues/issue-20772.stderr
index d64636310a3..4aecc7eab46 100644
--- a/src/test/ui/issues/issue-20772.stderr
+++ b/src/test/ui/issues/issue-20772.stderr
@@ -1,4 +1,4 @@
-error[E0391]: cycle detected when computing the supertraits of `T`
+error[E0391]: cycle detected when computing the super traits of `T` with associated type name `Item`
   --> $DIR/issue-20772.rs:1:1
    |
 LL | / trait T : Iterator<Item=Self::Item>
@@ -6,8 +6,8 @@ LL | |
 LL | | {}
    | |__^
    |
-   = note: ...which again requires computing the supertraits of `T`, completing the cycle
-note: cycle used when collecting item types in top-level module
+   = note: ...which again requires computing the super traits of `T` with associated type name `Item`, completing the cycle
+note: cycle used when computing the super traits of `T`
   --> $DIR/issue-20772.rs:1:1
    |
 LL | / trait T : Iterator<Item=Self::Item>
diff --git a/src/test/ui/issues/issue-20825.stderr b/src/test/ui/issues/issue-20825.stderr
index 5f9709d1c64..ccbe06d9c0d 100644
--- a/src/test/ui/issues/issue-20825.stderr
+++ b/src/test/ui/issues/issue-20825.stderr
@@ -1,11 +1,11 @@
-error[E0391]: cycle detected when computing the supertraits of `Processor`
+error[E0391]: cycle detected when computing the super traits of `Processor` with associated type name `Input`
   --> $DIR/issue-20825.rs:5:1
    |
 LL | pub trait Processor: Subscriber<Input = Self::Input> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: ...which again requires computing the supertraits of `Processor`, completing the cycle
-note: cycle used when collecting item types in top-level module
+   = note: ...which again requires computing the super traits of `Processor` with associated type name `Input`, completing the cycle
+note: cycle used when computing the super traits of `Processor`
   --> $DIR/issue-20825.rs:5:1
    |
 LL | pub trait Processor: Subscriber<Input = Self::Input> {
diff --git a/src/test/ui/issues/issue-22673.rs b/src/test/ui/issues/issue-22673.rs
index ba8057b684d..4b9b4d6b23d 100644
--- a/src/test/ui/issues/issue-22673.rs
+++ b/src/test/ui/issues/issue-22673.rs
@@ -1,5 +1,6 @@
-trait Expr : PartialEq<Self::Item> {
-    //~^ ERROR: cycle detected
+// check-pass
+
+trait Expr: PartialEq<Self::Item> {
     type Item;
 }
 
diff --git a/src/test/ui/issues/issue-22673.stderr b/src/test/ui/issues/issue-22673.stderr
deleted file mode 100644
index 9e7e4b218b1..00000000000
--- a/src/test/ui/issues/issue-22673.stderr
+++ /dev/null
@@ -1,16 +0,0 @@
-error[E0391]: cycle detected when computing the supertraits of `Expr`
-  --> $DIR/issue-22673.rs:1:1
-   |
-LL | trait Expr : PartialEq<Self::Item> {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-   |
-   = note: ...which again requires computing the supertraits of `Expr`, completing the cycle
-note: cycle used when collecting item types in top-level module
-  --> $DIR/issue-22673.rs:1:1
-   |
-LL | trait Expr : PartialEq<Self::Item> {
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0391`.