Auto merge of #100865 - compiler-errors:parent-substs-still, r=cjgillot

Don't drop parent substs when we have no generic parameters in `create_substs_for_ast_path`

This bug is being shadowed by an explicit check for `generics.params.is_empty()` in the only parent caller that could trigger it (`create_substs_for_associated_item`). I triggered it on another branch where I'm messing around with astconv stuff.

Also, the second commit simplifies `create_substs_for_associated_item`. Removing that explicit check I mentioned above^ and also the special case call to `Astconv::prohibit_generics` causes the UI test `src/test/ui/structs/struct-path-associated-type.stderr` to change, but I think that it's clearer now. The suggestion to remove the generics is actually useful.

2 files changed, 23 insertions, 11 deletions

diff --git a/src/test/ui/structs/struct-path-associated-type.rs b/src/test/ui/structs/struct-path-associated-type.rs
index f88572f8419..2dd7174a9be 100644
--- a/src/test/ui/structs/struct-path-associated-type.rs
+++ b/src/test/ui/structs/struct-path-associated-type.rs
@@ -13,7 +13,7 @@ fn f<T: Tr>() {
     //~^ ERROR expected struct, variant or union type, found associated type
     let z = T::A::<u8> {};
     //~^ ERROR expected struct, variant or union type, found associated type
-    //~| ERROR type arguments are not allowed on this type
+    //~| ERROR this associated type takes 0 generic arguments but 1 generic argument was supplied
     match S {
         T::A {} => {}
         //~^ ERROR expected struct, variant or union type, found associated type
@@ -22,7 +22,7 @@ fn f<T: Tr>() {
 
 fn g<T: Tr<A = S>>() {
     let s = T::A {}; // OK
-    let z = T::A::<u8> {}; //~ ERROR type arguments are not allowed on this type
+    let z = T::A::<u8> {}; //~ ERROR this associated type takes 0 generic arguments but 1 generic argument was supplied
     match S {
         T::A {} => {} // OK
     }
diff --git a/src/test/ui/structs/struct-path-associated-type.stderr b/src/test/ui/structs/struct-path-associated-type.stderr
index bdce0e1b331..abb445214f3 100644
--- a/src/test/ui/structs/struct-path-associated-type.stderr
+++ b/src/test/ui/structs/struct-path-associated-type.stderr
@@ -4,13 +4,19 @@ error[E0071]: expected struct, variant or union type, found associated type
 LL |     let s = T::A {};
    |             ^^^^ not a struct
 
-error[E0109]: type arguments are not allowed on this type
-  --> $DIR/struct-path-associated-type.rs:14:20
+error[E0107]: this associated type takes 0 generic arguments but 1 generic argument was supplied
+  --> $DIR/struct-path-associated-type.rs:14:16
    |
 LL |     let z = T::A::<u8> {};
-   |                -   ^^ type argument not allowed
+   |                ^------ help: remove these generics
    |                |
-   |                not allowed on this type
+   |                expected 0 generic arguments
+   |
+note: associated type defined here, with 0 generic parameters
+  --> $DIR/struct-path-associated-type.rs:4:10
+   |
+LL |     type A;
+   |          ^
 
 error[E0071]: expected struct, variant or union type, found associated type
   --> $DIR/struct-path-associated-type.rs:14:13
@@ -24,13 +30,19 @@ error[E0071]: expected struct, variant or union type, found associated type
 LL |         T::A {} => {}
    |         ^^^^ not a struct
 
-error[E0109]: type arguments are not allowed on this type
-  --> $DIR/struct-path-associated-type.rs:25:20
+error[E0107]: this associated type takes 0 generic arguments but 1 generic argument was supplied
+  --> $DIR/struct-path-associated-type.rs:25:16
    |
 LL |     let z = T::A::<u8> {};
-   |                -   ^^ type argument not allowed
+   |                ^------ help: remove these generics
    |                |
-   |                not allowed on this type
+   |                expected 0 generic arguments
+   |
+note: associated type defined here, with 0 generic parameters
+  --> $DIR/struct-path-associated-type.rs:4:10
+   |
+LL |     type A;
+   |          ^
 
 error[E0223]: ambiguous associated type
   --> $DIR/struct-path-associated-type.rs:32:13
@@ -52,5 +64,5 @@ LL |         S::A {} => {}
 
 error: aborting due to 8 previous errors
 
-Some errors have detailed explanations: E0071, E0109, E0223.
+Some errors have detailed explanations: E0071, E0107, E0223.
 For more information about an error, try `rustc --explain E0071`.