Rollup merge of #105944 - JohnTitor:issue-80816, r=compiler-errors

Add regression test for #80816

Closes #80816
r? `@compiler-errors`
Signed-off-by: Yuki Okushi <jtitor@2k36.org>

src/test/ui/inference/issue-80816.rs

@@ -0,0 +1,54 @@
+#![allow(unreachable_code)]
+
+use std::marker::PhantomData;
+use std::ops::Deref;
+use std::sync::Arc;
+
+pub struct Guard<T> {
+ _phantom: PhantomData<T>,
+}
+impl<T> Deref for Guard<T> {
+ type Target = T;
+ fn deref(&self) -> &T {
+ unimplemented!()
+ }
+}
+
+pub struct DirectDeref<T>(T);
+impl<T> Deref for DirectDeref<Arc<T>> {
+ type Target = T;
+ fn deref(&self) -> &T {
+ unimplemented!()
+ }
+}
+
+pub trait Access<T> {
+ type Guard: Deref<Target = T>;
+ fn load(&self) -> Self::Guard {
+ unimplemented!()
+ }
+}
+impl<T, A: Access<T>, P: Deref<Target = A>> Access<T> for P {
+ //~^ NOTE: required for `Arc<ArcSwapAny<Arc<usize>>>` to implement `Access<_>`
+ type Guard = A::Guard;
+}
+impl<T> Access<T> for ArcSwapAny<T> {
+ //~^ NOTE: multiple `impl`s satisfying `ArcSwapAny<Arc<usize>>: Access<_>` found
+ type Guard = Guard<T>;
+}
+impl<T> Access<T> for ArcSwapAny<Arc<T>> {
+ type Guard = DirectDeref<Arc<T>>;
+}
+
+pub struct ArcSwapAny<T> {
+ _phantom_arc: PhantomData<T>,
+}
+
+pub fn foo() {
+ let s: Arc<ArcSwapAny<Arc<usize>>> = unimplemented!();
+ let guard: Guard<Arc<usize>> = s.load();
+ //~^ ERROR: type annotations needed
+ //~| HELP: try using a fully qualified path to specify the expected types
+}
+
+fn main() {}

src/test/ui/inference/issue-80816.stderr

@@ -0,0 +1,27 @@
+error[E0283]: type annotations needed
+ --> $DIR/issue-80816.rs:49:38
+ |
+LL | let guard: Guard<Arc<usize>> = s.load();
+ | ^^^^
+ |
+note: multiple `impl`s satisfying `ArcSwapAny<Arc<usize>>: Access<_>` found
+ --> $DIR/issue-80816.rs:35:1
+ |
+LL | impl<T> Access<T> for ArcSwapAny<T> {
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+...
+LL | impl<T> Access<T> for ArcSwapAny<Arc<T>> {
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: required for `Arc<ArcSwapAny<Arc<usize>>>` to implement `Access<_>`
+ --> $DIR/issue-80816.rs:31:45
+ |
+LL | impl<T, A: Access<T>, P: Deref<Target = A>> Access<T> for P {
+ | ^^^^^^^^^ ^
+help: try using a fully qualified path to specify the expected types
+ |
+LL | let guard: Guard<Arc<usize>> = <Arc<ArcSwapAny<Arc<usize>>> as Access<T>>::load(&s);
+ | ++++++++++++++++++++++++++++++++++++++++++++++++++ ~
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0283`.