Auto merge of #129073 - compiler-errors:receiver-variance, r=lcnr

Relate receiver invariantly in method probe for `Mode::Path`

Effectively reverts part of #126128
Fixes #126227

This PR changes method probing to use equality for fully path-based method lookup, and subtyping for receiver `.` method lookup.

r? lcnr

15 files changed, 117 insertions, 50 deletions

diff --git a/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg.rs b/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg.rs
index e2fc2961a44..a33d4928f01 100644
--- a/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg.rs
+++ b/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg.rs
@@ -7,4 +7,5 @@ impl Fail<i32> {
 
 fn main() {
     Fail::<()>::C
+    //~^ ERROR no associated item named `C` found for struct `Fail<()>` in the current scope
 }
diff --git a/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg.stderr b/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg.stderr
index f0a6ccf243a..c5816393107 100644
--- a/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg.stderr
+++ b/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg.stderr
@@ -7,6 +7,19 @@ LL | struct Fail<T>;
    = help: consider removing `T`, referring to it in a field, or using a marker such as `PhantomData`
    = help: if you intended `T` to be a const parameter, use `const T: /* Type */` instead
 
-error: aborting due to 1 previous error
+error[E0599]: no associated item named `C` found for struct `Fail<()>` in the current scope
+  --> $DIR/wrong-projection-self-ty-invalid-bivariant-arg.rs:9:17
+   |
+LL | struct Fail<T>;
+   | -------------- associated item `C` not found for this struct
+...
+LL |     Fail::<()>::C
+   |                 ^ associated item not found in `Fail<()>`
+   |
+   = note: the associated item was found for
+           - `Fail<i32>`
+
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0392`.
+Some errors have detailed explanations: E0392, E0599.
+For more information about an error, try `rustc --explain E0392`.
diff --git a/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg2.rs b/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg2.rs
index cb53d902ba1..d891b7bd62b 100644
--- a/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg2.rs
+++ b/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg2.rs
@@ -14,4 +14,5 @@ impl Fail<i32, i32> {
 fn main() {
     Fail::<i32, u32>::C
     //~^ ERROR: type mismatch
+    //~| ERROR no associated item named `C` found for struct `Fail<i32, u32>` in the current scope
 }
diff --git a/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg2.stderr b/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg2.stderr
index 0d63b7f5b29..18d458aea80 100644
--- a/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg2.stderr
+++ b/tests/ui/associated-consts/wrong-projection-self-ty-invalid-bivariant-arg2.stderr
@@ -1,3 +1,15 @@
+error[E0599]: no associated item named `C` found for struct `Fail<i32, u32>` in the current scope
+  --> $DIR/wrong-projection-self-ty-invalid-bivariant-arg2.rs:15:23
+   |
+LL | struct Fail<T: Proj<Assoc = U>, U>(T);
+   | ---------------------------------- associated item `C` not found for this struct
+...
+LL |     Fail::<i32, u32>::C
+   |                       ^ associated item not found in `Fail<i32, u32>`
+   |
+   = note: the associated item was found for
+           - `Fail<i32, i32>`
+
 error[E0271]: type mismatch resolving `<i32 as Proj>::Assoc == u32`
   --> $DIR/wrong-projection-self-ty-invalid-bivariant-arg2.rs:15:5
    |
@@ -15,6 +27,7 @@ note: required by a bound in `Fail`
 LL | struct Fail<T: Proj<Assoc = U>, U>(T);
    |                     ^^^^^^^^^ required by this bound in `Fail`
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0271`.
+Some errors have detailed explanations: E0271, E0599.
+For more information about an error, try `rustc --explain E0271`.
diff --git a/tests/ui/coercion/coerce-issue-49593-box-never.fallback.stderr b/tests/ui/coercion/coerce-issue-49593-box-never.fallback.stderr
deleted file mode 100644
index ef5633f7134..00000000000
--- a/tests/ui/coercion/coerce-issue-49593-box-never.fallback.stderr
+++ /dev/null
@@ -1,11 +0,0 @@
-error[E0277]: the trait bound `(): std::error::Error` is not satisfied
-  --> $DIR/coerce-issue-49593-box-never.rs:18:5
-   |
-LL |     Box::<_ /* ! */>::new(x)
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^ the trait `std::error::Error` is not implemented for `()`
-   |
-   = note: required for the cast from `Box<()>` to `Box<(dyn std::error::Error + 'static)>`
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/coercion/coerce-issue-49593-box-never.rs b/tests/ui/coercion/coerce-issue-49593-box-never.rs
index 53071be47dc..e5569592045 100644
--- a/tests/ui/coercion/coerce-issue-49593-box-never.rs
+++ b/tests/ui/coercion/coerce-issue-49593-box-never.rs
@@ -1,5 +1,5 @@
 //@ revisions: nofallback fallback
-//@check-fail
+//@[fallback] check-pass
 
 #![feature(never_type)]
 #![cfg_attr(fallback, feature(never_type_fallback))]
@@ -13,10 +13,10 @@ fn raw_ptr_box<T>(t: T) -> *mut T {
 }
 
 fn foo(x: !) -> Box<dyn Error> {
-    // Subtyping during method resolution will generate new inference vars and
-    // subtype them. Thus fallback will not fall back to `!`, but `()` instead.
+    // Method resolution will generate new inference vars and relate them.
+    // Thus fallback will not fall back to `!`, but `()` instead.
     Box::<_ /* ! */>::new(x)
-    //~^ ERROR trait bound `(): std::error::Error` is not satisfied
+    //[nofallback]~^ ERROR trait bound `(): std::error::Error` is not satisfied
 }
 
 fn foo_raw_ptr(x: !) -> *mut dyn Error {
diff --git a/tests/ui/const-generics/generic_arg_infer/issue-91614.stderr b/tests/ui/const-generics/generic_arg_infer/issue-91614.stderr
index 217f609459e..b88fe966b77 100644
--- a/tests/ui/const-generics/generic_arg_infer/issue-91614.stderr
+++ b/tests/ui/const-generics/generic_arg_infer/issue-91614.stderr
@@ -8,7 +8,7 @@ note: required by a const generic parameter in `Mask::<T, N>::splat`
   --> $SRC_DIR/core/src/../../portable-simd/crates/core_simd/src/masks.rs:LL:COL
 help: consider giving `y` an explicit type, where the value of const parameter `N` is specified
    |
-LL |     let y: Mask<T, N> = Mask::<_, _>::splat(false);
+LL |     let y: Mask<_, N> = Mask::<_, _>::splat(false);
    |          ++++++++++++
 
 error[E0284]: type annotations needed for `Mask<_, _>`
@@ -21,7 +21,7 @@ note: required by a const generic parameter in `Mask`
   --> $SRC_DIR/core/src/../../portable-simd/crates/core_simd/src/masks.rs:LL:COL
 help: consider giving `y` an explicit type, where the value of const parameter `N` is specified
    |
-LL |     let y: Mask<T, N> = Mask::<_, _>::splat(false);
+LL |     let y: Mask<_, N> = Mask::<_, _>::splat(false);
    |          ++++++++++++
 
 error: aborting due to 2 previous errors
diff --git a/tests/ui/impl-trait/issues/issue-62742.rs b/tests/ui/impl-trait/issues/issue-62742.rs
index 56c63a1daa8..c64278c2c5b 100644
--- a/tests/ui/impl-trait/issues/issue-62742.rs
+++ b/tests/ui/impl-trait/issues/issue-62742.rs
@@ -2,7 +2,8 @@ use std::marker::PhantomData;
 
 fn a() {
     WrongImpl::foo(0i32);
-    //~^ ERROR overflow assigning `_` to `[_]`
+    //~^ ERROR the function or associated item `foo` exists for struct `SafeImpl<_, RawImpl<_>>`, but its trait bounds were not satisfied
+    //~| ERROR the trait bound `RawImpl<_>: Raw<_>` is not satisfied
 }
 
 fn b() {
diff --git a/tests/ui/impl-trait/issues/issue-62742.stderr b/tests/ui/impl-trait/issues/issue-62742.stderr
index 7a1bcfc70d5..94822e41ccd 100644
--- a/tests/ui/impl-trait/issues/issue-62742.stderr
+++ b/tests/ui/impl-trait/issues/issue-62742.stderr
@@ -1,11 +1,43 @@
-error[E0275]: overflow assigning `_` to `[_]`
+error[E0599]: the function or associated item `foo` exists for struct `SafeImpl<_, RawImpl<_>>`, but its trait bounds were not satisfied
   --> $DIR/issue-62742.rs:4:16
    |
 LL |     WrongImpl::foo(0i32);
-   |                ^^^
+   |                ^^^ function or associated item cannot be called on `SafeImpl<_, RawImpl<_>>` due to unsatisfied trait bounds
+...
+LL | pub struct RawImpl<T>(PhantomData<T>);
+   | --------------------- doesn't satisfy `RawImpl<_>: Raw<_>`
+...
+LL | pub struct SafeImpl<T: ?Sized, A: Raw<T>>(PhantomData<(A, T)>);
+   | ----------------------------------------- function or associated item `foo` not found for this struct
+   |
+note: trait bound `RawImpl<_>: Raw<_>` was not satisfied
+  --> $DIR/issue-62742.rs:35:20
+   |
+LL | impl<T: ?Sized, A: Raw<T>> SafeImpl<T, A> {
+   |                    ^^^^^^  --------------
+   |                    |
+   |                    unsatisfied trait bound introduced here
+note: the trait `Raw` must be implemented
+  --> $DIR/issue-62742.rs:19:1
+   |
+LL | pub trait Raw<T: ?Sized> {
+   | ^^^^^^^^^^^^^^^^^^^^^^^^
+
+error[E0277]: the trait bound `RawImpl<_>: Raw<_>` is not satisfied
+  --> $DIR/issue-62742.rs:4:5
+   |
+LL |     WrongImpl::foo(0i32);
+   |     ^^^^^^^^^ the trait `Raw<_>` is not implemented for `RawImpl<_>`
+   |
+   = help: the trait `Raw<[_]>` is implemented for `RawImpl<_>`
+note: required by a bound in `SafeImpl`
+  --> $DIR/issue-62742.rs:33:35
+   |
+LL | pub struct SafeImpl<T: ?Sized, A: Raw<T>>(PhantomData<(A, T)>);
+   |                                   ^^^^^^ required by this bound in `SafeImpl`
 
 error[E0599]: the function or associated item `foo` exists for struct `SafeImpl<(), RawImpl<()>>`, but its trait bounds were not satisfied
-  --> $DIR/issue-62742.rs:9:22
+  --> $DIR/issue-62742.rs:10:22
    |
 LL |     WrongImpl::<()>::foo(0i32);
    |                      ^^^ function or associated item cannot be called on `SafeImpl<(), RawImpl<()>>` due to unsatisfied trait bounds
@@ -17,20 +49,20 @@ LL | pub struct SafeImpl<T: ?Sized, A: Raw<T>>(PhantomData<(A, T)>);
    | ----------------------------------------- function or associated item `foo` not found for this struct
    |
 note: trait bound `RawImpl<()>: Raw<()>` was not satisfied
-  --> $DIR/issue-62742.rs:34:20
+  --> $DIR/issue-62742.rs:35:20
    |
 LL | impl<T: ?Sized, A: Raw<T>> SafeImpl<T, A> {
    |                    ^^^^^^  --------------
    |                    |
    |                    unsatisfied trait bound introduced here
 note: the trait `Raw` must be implemented
-  --> $DIR/issue-62742.rs:18:1
+  --> $DIR/issue-62742.rs:19:1
    |
 LL | pub trait Raw<T: ?Sized> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0277]: the trait bound `RawImpl<()>: Raw<()>` is not satisfied
-  --> $DIR/issue-62742.rs:9:5
+  --> $DIR/issue-62742.rs:10:5
    |
 LL |     WrongImpl::<()>::foo(0i32);
    |     ^^^^^^^^^^^^^^^ the trait `Raw<()>` is not implemented for `RawImpl<()>`
@@ -38,12 +70,12 @@ LL |     WrongImpl::<()>::foo(0i32);
    = help: the trait `Raw<[()]>` is implemented for `RawImpl<()>`
    = help: for that trait implementation, expected `[()]`, found `()`
 note: required by a bound in `SafeImpl`
-  --> $DIR/issue-62742.rs:32:35
+  --> $DIR/issue-62742.rs:33:35
    |
 LL | pub struct SafeImpl<T: ?Sized, A: Raw<T>>(PhantomData<(A, T)>);
    |                                   ^^^^^^ required by this bound in `SafeImpl`
 
-error: aborting due to 3 previous errors
+error: aborting due to 4 previous errors
 
-Some errors have detailed explanations: E0275, E0277, E0599.
-For more information about an error, try `rustc --explain E0275`.
+Some errors have detailed explanations: E0277, E0599.
+For more information about an error, try `rustc --explain E0277`.
diff --git a/tests/ui/inference/need_type_info/type-alias-indirect.stderr b/tests/ui/inference/need_type_info/type-alias-indirect.stderr
index 5c5b4c149c1..535c0044aec 100644
--- a/tests/ui/inference/need_type_info/type-alias-indirect.stderr
+++ b/tests/ui/inference/need_type_info/type-alias-indirect.stderr
@@ -2,7 +2,7 @@ error[E0282]: type annotations needed
   --> $DIR/type-alias-indirect.rs:14:5
    |
 LL |     IndirectAlias::new();
-   |     ^^^^^^^^^^^^^^^^^^^^ cannot infer type for type parameter `T` declared on the type alias `IndirectAlias`
+   |     ^^^^^^^^^^^^^ cannot infer type for type parameter `T` declared on the type alias `IndirectAlias`
 
 error: aborting due to 1 previous error
 
diff --git a/tests/ui/inference/need_type_info/type-alias.stderr b/tests/ui/inference/need_type_info/type-alias.stderr
index fd9bcf2fe3f..2c39a3f5646 100644
--- a/tests/ui/inference/need_type_info/type-alias.stderr
+++ b/tests/ui/inference/need_type_info/type-alias.stderr
@@ -2,19 +2,19 @@ error[E0282]: type annotations needed
   --> $DIR/type-alias.rs:12:5
    |
 LL |     DirectAlias::new()
-   |     ^^^^^^^^^^^^^^^^^^ cannot infer type for type parameter `T` declared on the type alias `DirectAlias`
+   |     ^^^^^^^^^^^^^^^^^^ cannot infer type for type parameter `T`
 
 error[E0282]: type annotations needed
   --> $DIR/type-alias.rs:18:5
    |
 LL |     IndirectAlias::new();
-   |     ^^^^^^^^^^^^^^^^^^^^ cannot infer type for type parameter `T` declared on the type alias `IndirectAlias`
+   |     ^^^^^^^^^^^^^ cannot infer type for type parameter `T` declared on the type alias `IndirectAlias`
 
 error[E0282]: type annotations needed
   --> $DIR/type-alias.rs:32:5
    |
 LL |     DirectButWithDefaultAlias::new();
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type for type parameter `T` declared on the type alias `DirectButWithDefaultAlias`
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ cannot infer type for type parameter `T`
 
 error: aborting due to 3 previous errors
 
diff --git a/tests/ui/methods/receiver-equality.rs b/tests/ui/methods/receiver-equality.rs
new file mode 100644
index 00000000000..891435a425e
--- /dev/null
+++ b/tests/ui/methods/receiver-equality.rs
@@ -0,0 +1,16 @@
+// Tests that we probe receivers invariantly when using path-based method lookup.
+
+struct B<T>(T);
+
+impl B<fn(&'static ())> {
+    fn method(self) {
+        println!("hey");
+    }
+}
+
+fn foo(y: B<fn(&'static ())>) {
+    B::<for<'a> fn(&'a ())>::method(y);
+    //~^ ERROR no function or associated item named `method` found
+}
+
+fn main() {}
diff --git a/tests/ui/methods/receiver-equality.stderr b/tests/ui/methods/receiver-equality.stderr
new file mode 100644
index 00000000000..cea3340e386
--- /dev/null
+++ b/tests/ui/methods/receiver-equality.stderr
@@ -0,0 +1,12 @@
+error[E0599]: no function or associated item named `method` found for struct `B<for<'a> fn(&'a ())>` in the current scope
+  --> $DIR/receiver-equality.rs:12:30
+   |
+LL | struct B<T>(T);
+   | ----------- function or associated item `method` not found for this struct
+...
+LL |     B::<for<'a> fn(&'a ())>::method(y);
+   |                              ^^^^^^ function or associated item not found in `B<fn(&())>`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0599`.
diff --git a/tests/ui/suggestions/mut-borrow-needed-by-trait.rs b/tests/ui/suggestions/mut-borrow-needed-by-trait.rs
index 924bfd82eb8..66e1e77c905 100644
--- a/tests/ui/suggestions/mut-borrow-needed-by-trait.rs
+++ b/tests/ui/suggestions/mut-borrow-needed-by-trait.rs
@@ -17,7 +17,6 @@ fn main() {
     let fp = BufWriter::new(fp);
     //~^ ERROR the trait bound `&dyn std::io::Write: std::io::Write` is not satisfied
     //~| ERROR the trait bound `&dyn std::io::Write: std::io::Write` is not satisfied
-    //~| ERROR the trait bound `&dyn std::io::Write: std::io::Write` is not satisfied
 
     writeln!(fp, "hello world").unwrap(); //~ ERROR the method
 }
diff --git a/tests/ui/suggestions/mut-borrow-needed-by-trait.stderr b/tests/ui/suggestions/mut-borrow-needed-by-trait.stderr
index b2f9150142f..09a9b1d3b34 100644
--- a/tests/ui/suggestions/mut-borrow-needed-by-trait.stderr
+++ b/tests/ui/suggestions/mut-borrow-needed-by-trait.stderr
@@ -14,16 +14,6 @@ error[E0277]: the trait bound `&dyn std::io::Write: std::io::Write` is not satis
   --> $DIR/mut-borrow-needed-by-trait.rs:17:14
    |
 LL |     let fp = BufWriter::new(fp);
-   |              ^^^^^^^^^ the trait `std::io::Write` is not implemented for `&dyn std::io::Write`
-   |
-   = note: `std::io::Write` is implemented for `&mut dyn std::io::Write`, but not for `&dyn std::io::Write`
-note: required by a bound in `BufWriter`
-  --> $SRC_DIR/std/src/io/buffered/bufwriter.rs:LL:COL
-
-error[E0277]: the trait bound `&dyn std::io::Write: std::io::Write` is not satisfied
-  --> $DIR/mut-borrow-needed-by-trait.rs:17:14
-   |
-LL |     let fp = BufWriter::new(fp);
    |              ^^^^^^^^^^^^^^^^^^ the trait `std::io::Write` is not implemented for `&dyn std::io::Write`
    |
    = note: `std::io::Write` is implemented for `&mut dyn std::io::Write`, but not for `&dyn std::io::Write`
@@ -31,13 +21,13 @@ note: required by a bound in `BufWriter`
   --> $SRC_DIR/std/src/io/buffered/bufwriter.rs:LL:COL
 
 error[E0599]: the method `write_fmt` exists for struct `BufWriter<&dyn Write>`, but its trait bounds were not satisfied
-  --> $DIR/mut-borrow-needed-by-trait.rs:22:14
+  --> $DIR/mut-borrow-needed-by-trait.rs:21:14
    |
 LL |     writeln!(fp, "hello world").unwrap();
    |     ---------^^---------------- method cannot be called on `BufWriter<&dyn Write>` due to unsatisfied trait bounds
    |
 note: must implement `io::Write`, `fmt::Write`, or have a `write_fmt` method
-  --> $DIR/mut-borrow-needed-by-trait.rs:22:14
+  --> $DIR/mut-borrow-needed-by-trait.rs:21:14
    |
 LL |     writeln!(fp, "hello world").unwrap();
    |              ^^
@@ -45,7 +35,7 @@ LL |     writeln!(fp, "hello world").unwrap();
            `&dyn std::io::Write: std::io::Write`
            which is required by `BufWriter<&dyn std::io::Write>: std::io::Write`
 
-error: aborting due to 4 previous errors
+error: aborting due to 3 previous errors
 
 Some errors have detailed explanations: E0277, E0599.
 For more information about an error, try `rustc --explain E0277`.