Rollup merge of #103609 - BoxyUwU:fix_impl_self_cycle, r=compiler-errors

Emit a nicer error on `impl Self {`

currently it emits a "cycle detected error" but this PR makes it emit a more user friendly error specifically saying that `Self` is disallowed in that position. this is a pretty hacky fix so i dont expect this to be merged (I basically only made this PR because i wanted to see if CI passes)

r? ``@compiler-errors``

4 files changed, 27 insertions, 74 deletions

diff --git a/src/test/ui/resolve/issue-23305.rs b/src/test/ui/resolve/issue-23305.rs
index 95635e12a63..6d7fe7c50a2 100644
--- a/src/test/ui/resolve/issue-23305.rs
+++ b/src/test/ui/resolve/issue-23305.rs
@@ -3,6 +3,6 @@ pub trait ToNbt<T> {
 }
 
 impl dyn ToNbt<Self> {}
-//~^ ERROR cycle detected
+//~^ ERROR `Self` is not valid in the self type of an impl block
 
 fn main() {}
diff --git a/src/test/ui/resolve/issue-23305.stderr b/src/test/ui/resolve/issue-23305.stderr
index 20aeb7b995a..aad1b583a32 100644
--- a/src/test/ui/resolve/issue-23305.stderr
+++ b/src/test/ui/resolve/issue-23305.stderr
@@ -1,22 +1,10 @@
-error[E0391]: cycle detected when computing type of `<impl at $DIR/issue-23305.rs:5:1: 5:21>`
+error: `Self` is not valid in the self type of an impl block
   --> $DIR/issue-23305.rs:5:16
    |
 LL | impl dyn ToNbt<Self> {}
    |                ^^^^
    |
-   = note: ...which immediately requires computing type of `<impl at $DIR/issue-23305.rs:5:1: 5:21>` again
-note: cycle used when collecting item types in top-level module
-  --> $DIR/issue-23305.rs:1:1
-   |
-LL | / pub trait ToNbt<T> {
-LL | |     fn new(val: T) -> Self;
-LL | | }
-LL | |
-...  |
-LL | |
-LL | | fn main() {}
-   | |____________^
+   = note: replace `Self` with a different type
 
 error: aborting due to previous error
 
-For more information about this error, try `rustc --explain E0391`.
diff --git a/src/test/ui/resolve/resolve-self-in-impl.rs b/src/test/ui/resolve/resolve-self-in-impl.rs
index 024fdc51ea3..d0872d1b76f 100644
--- a/src/test/ui/resolve/resolve-self-in-impl.rs
+++ b/src/test/ui/resolve/resolve-self-in-impl.rs
@@ -11,10 +11,11 @@ impl Tr for S where Self: Copy {} // OK
 impl Tr for S where S<Self>: Copy {} // OK
 impl Tr for S where Self::A: Copy {} // OK
 
-impl Tr for Self {} //~ ERROR cycle detected
-impl Tr for S<Self> {} //~ ERROR cycle detected
-impl Self {} //~ ERROR cycle detected
-impl S<Self> {} //~ ERROR cycle detected
+impl Tr for Self {} //~ ERROR `Self` is not valid in the self type of an impl block
+impl Tr for S<Self> {} //~ ERROR `Self` is not valid in the self type of an impl block
+impl Self {} //~ ERROR `Self` is not valid in the self type of an impl block
+impl S<Self> {} //~ ERROR `Self` is not valid in the self type of an impl block
+impl (Self, Self) {} //~ ERROR `Self` is not valid in the self type of an impl block
 impl Tr<Self::A> for S {} //~ ERROR cycle detected
 
 fn main() {}
diff --git a/src/test/ui/resolve/resolve-self-in-impl.stderr b/src/test/ui/resolve/resolve-self-in-impl.stderr
index aa99c1a3335..9f9ed68898f 100644
--- a/src/test/ui/resolve/resolve-self-in-impl.stderr
+++ b/src/test/ui/resolve/resolve-self-in-impl.stderr
@@ -1,86 +1,50 @@
-error[E0391]: cycle detected when computing type of `<impl at $DIR/resolve-self-in-impl.rs:14:1: 14:17>`
+error: `Self` is not valid in the self type of an impl block
   --> $DIR/resolve-self-in-impl.rs:14:13
    |
 LL | impl Tr for Self {}
    |             ^^^^
    |
-   = note: ...which immediately requires computing type of `<impl at $DIR/resolve-self-in-impl.rs:14:1: 14:17>` again
-note: cycle used when collecting item types in top-level module
-  --> $DIR/resolve-self-in-impl.rs:1:1
-   |
-LL | / #![feature(associated_type_defaults)]
-LL | |
-LL | | struct S<T = u8>(T);
-LL | | trait Tr<T = u8> {
-...  |
-LL | |
-LL | | fn main() {}
-   | |____________^
+   = note: replace `Self` with a different type
 
-error[E0391]: cycle detected when computing type of `<impl at $DIR/resolve-self-in-impl.rs:15:1: 15:20>`
+error: `Self` is not valid in the self type of an impl block
   --> $DIR/resolve-self-in-impl.rs:15:15
    |
 LL | impl Tr for S<Self> {}
    |               ^^^^
    |
-   = note: ...which immediately requires computing type of `<impl at $DIR/resolve-self-in-impl.rs:15:1: 15:20>` again
-note: cycle used when collecting item types in top-level module
-  --> $DIR/resolve-self-in-impl.rs:1:1
-   |
-LL | / #![feature(associated_type_defaults)]
-LL | |
-LL | | struct S<T = u8>(T);
-LL | | trait Tr<T = u8> {
-...  |
-LL | |
-LL | | fn main() {}
-   | |____________^
+   = note: replace `Self` with a different type
 
-error[E0391]: cycle detected when computing type of `<impl at $DIR/resolve-self-in-impl.rs:16:1: 16:10>`
+error: `Self` is not valid in the self type of an impl block
   --> $DIR/resolve-self-in-impl.rs:16:6
    |
 LL | impl Self {}
    |      ^^^^
    |
-   = note: ...which immediately requires computing type of `<impl at $DIR/resolve-self-in-impl.rs:16:1: 16:10>` again
-note: cycle used when collecting item types in top-level module
-  --> $DIR/resolve-self-in-impl.rs:1:1
-   |
-LL | / #![feature(associated_type_defaults)]
-LL | |
-LL | | struct S<T = u8>(T);
-LL | | trait Tr<T = u8> {
-...  |
-LL | |
-LL | | fn main() {}
-   | |____________^
+   = note: replace `Self` with a different type
 
-error[E0391]: cycle detected when computing type of `<impl at $DIR/resolve-self-in-impl.rs:17:1: 17:13>`
+error: `Self` is not valid in the self type of an impl block
   --> $DIR/resolve-self-in-impl.rs:17:8
    |
 LL | impl S<Self> {}
    |        ^^^^
    |
-   = note: ...which immediately requires computing type of `<impl at $DIR/resolve-self-in-impl.rs:17:1: 17:13>` again
-note: cycle used when collecting item types in top-level module
-  --> $DIR/resolve-self-in-impl.rs:1:1
+   = note: replace `Self` with a different type
+
+error: `Self` is not valid in the self type of an impl block
+  --> $DIR/resolve-self-in-impl.rs:18:7
    |
-LL | / #![feature(associated_type_defaults)]
-LL | |
-LL | | struct S<T = u8>(T);
-LL | | trait Tr<T = u8> {
-...  |
-LL | |
-LL | | fn main() {}
-   | |____________^
+LL | impl (Self, Self) {}
+   |       ^^^^  ^^^^
+   |
+   = note: replace `Self` with a different type
 
-error[E0391]: cycle detected when computing trait implemented by `<impl at $DIR/resolve-self-in-impl.rs:18:1: 18:23>`
-  --> $DIR/resolve-self-in-impl.rs:18:1
+error[E0391]: cycle detected when computing trait implemented by `<impl at $DIR/resolve-self-in-impl.rs:19:1: 19:23>`
+  --> $DIR/resolve-self-in-impl.rs:19:1
    |
 LL | impl Tr<Self::A> for S {}
    | ^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: ...which immediately requires computing trait implemented by `<impl at $DIR/resolve-self-in-impl.rs:18:1: 18:23>` again
+   = note: ...which immediately requires computing trait implemented by `<impl at $DIR/resolve-self-in-impl.rs:19:1: 19:23>` again
 note: cycle used when collecting item types in top-level module
   --> $DIR/resolve-self-in-impl.rs:1:1
    |
@@ -93,6 +57,6 @@ LL | |
 LL | | fn main() {}
    | |____________^
 
-error: aborting due to 5 previous errors
+error: aborting due to 6 previous errors
 
 For more information about this error, try `rustc --explain E0391`.