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

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -1388,10 +1388,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  // This also occurs for an enum variant on a type alias.
  let impl_ty = self.normalize(span, tcx.type_of(impl_def_id).instantiate(tcx, args));
  let self_ty = self.normalize(span, self_ty);
- match self.at(&self.misc(span), self.param_env).sub(
+ match self.at(&self.misc(span), self.param_env).eq(
  DefineOpaqueTypes::Yes,
- self_ty,
  impl_ty,
+ self_ty,
  ) {
  Ok(ok) => self.register_infer_ok_obligations(ok),
  Err(_) => {

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -621,6 +621,16 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
  self.unsatisfied_predicates.borrow_mut().clear();
  }
 
+ /// When we're looking up a method by path (UFCS), we relate the receiver
+ /// types invariantly. When we are looking up a method by the `.` operator,
+ /// we relate them covariantly.
+ fn variance(&self) -> ty::Variance {
+ match self.mode {
+ Mode::MethodCall => ty::Covariant,
+ Mode::Path => ty::Invariant,
+ }
+ }
+
  ///////////////////////////////////////////////////////////////////////////
  // CANDIDATE ASSEMBLY
 
@@ -1443,7 +1453,8 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
  (xform_self_ty, xform_ret_ty) =
  self.xform_self_ty(probe.item, impl_ty, impl_args);
  xform_self_ty = ocx.normalize(cause, self.param_env, xform_self_ty);
- match ocx.sup(cause, self.param_env, xform_self_ty, self_ty) {
+ match ocx.relate(cause, self.param_env, self.variance(), self_ty, xform_self_ty)
+ {
  Ok(()) => {}
  Err(err) => {
  debug!("--> cannot relate self-types {:?}", err);
@@ -1514,7 +1525,13 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
  {
  return ProbeResult::NoMatch;
  }
- _ => match ocx.sup(cause, self.param_env, xform_self_ty, self_ty) {
+ _ => match ocx.relate(
+ cause,
+ self.param_env,
+ self.variance(),
+ self_ty,
+ xform_self_ty,
+ ) {
  Ok(()) => {}
  Err(err) => {
  debug!("--> cannot relate self-types {:?}", err);
@@ -1560,7 +1577,8 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
  (xform_self_ty, xform_ret_ty) =
  self.xform_self_ty(probe.item, trait_ref.self_ty(), trait_ref.args);
  xform_self_ty = ocx.normalize(cause, self.param_env, xform_self_ty);
- match ocx.sup(cause, self.param_env, xform_self_ty, self_ty) {
+ match ocx.relate(cause, self.param_env, self.variance(), self_ty, xform_self_ty)
+ {
  Ok(()) => {}
  Err(err) => {
  debug!("--> cannot relate self-types {:?}", err);
@@ -1603,7 +1621,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
  }
 
  debug!("comparing return_ty {:?} with xform ret ty {:?}", return_ty, xform_ret_ty);
- match ocx.sup(cause, self.param_env, return_ty, xform_ret_ty) {
+ match ocx.relate(cause, self.param_env, self.variance(), xform_ret_ty, return_ty) {
  Ok(()) => {}
  Err(_) => {
  result = ProbeResult::BadReturnType;

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
 }

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`.

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
 }

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`.

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 {

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

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() {

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
@@ -17,33 +49,33 @@ 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<()>`
  |
  = 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`.

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
 

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
 

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() {}

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`.

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
 }

tests/ui/suggestions/mut-borrow-needed-by-trait.stderr

@@ -10,16 +10,6 @@ LL | let fp = BufWriter::new(fp);
 note: required by a bound in `BufWriter::<W>::new`
  --> $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`
-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
  |
@@ -31,21 +21,21 @@ 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();
  | ^^
  = note: the following trait bounds were not satisfied:
  `&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`.