From d43683f2e905d34ab289882c16124deb5ed09edd Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Sun, 18 Jun 2023 22:10:07 +0000
Subject: [PATCH] Treat TAIT equation as always ambiguous in coherence
---
compiler/rustc_infer/src/infer/combine.rs | 11 +++----
.../tests/ui/from_over_into_unfixable.rs | 6 ----
.../tests/ui/from_over_into_unfixable.stderr | 33 ++++++++++++++-----
...coherence-treats-tait-ambig.current.stderr | 13 ++++++++
.../coherence-treats-tait-ambig.next.stderr | 13 ++++++++
.../impl-trait/coherence-treats-tait-ambig.rs | 19 +++++++++++
6 files changed, 74 insertions(+), 21 deletions(-)
create mode 100644 tests/ui/impl-trait/coherence-treats-tait-ambig.current.stderr
create mode 100644 tests/ui/impl-trait/coherence-treats-tait-ambig.next.stderr
create mode 100644 tests/ui/impl-trait/coherence-treats-tait-ambig.rs
diff --git a/compiler/rustc_infer/src/infer/combine.rs b/compiler/rustc_infer/src/infer/combine.rs
index 152c56572b6..12cb86d7d72 100644
--- a/compiler/rustc_infer/src/infer/combine.rs
+++ b/compiler/rustc_infer/src/infer/combine.rs
@@ -124,13 +124,10 @@ impl<'tcx> InferCtxt<'tcx> {
}
// During coherence, opaque types should be treated as *possibly*
- // equal to each other, even if their generic params differ, as
- // they could resolve to the same hidden type, even for different
- // generic params.
- (
- &ty::Alias(ty::Opaque, ty::AliasTy { def_id: a_def_id, .. }),
- &ty::Alias(ty::Opaque, ty::AliasTy { def_id: b_def_id, .. }),
- ) if self.intercrate && a_def_id == b_def_id => {
+ // equal to any other type (except for possibly itself). This is an
+ // extremely heavy hammer, but can be relaxed in a fowards-compatible
+ // way later.
+ (&ty::Alias(ty::Opaque, _), _) | (_, &ty::Alias(ty::Opaque, _)) if self.intercrate => {
relation.register_predicates([ty::Binder::dummy(ty::PredicateKind::Ambiguous)]);
Ok(a)
}
diff --git a/src/tools/clippy/tests/ui/from_over_into_unfixable.rs b/src/tools/clippy/tests/ui/from_over_into_unfixable.rs
index bd62c655216..3b280b7488a 100644
--- a/src/tools/clippy/tests/ui/from_over_into_unfixable.rs
+++ b/src/tools/clippy/tests/ui/from_over_into_unfixable.rs
@@ -32,10 +32,4 @@ impl Into<u8> for ContainsVal {
}
}
-type Opaque = impl Sized;
-struct IntoOpaque;
-impl Into<Opaque> for IntoOpaque {
- fn into(self) -> Opaque {}
-}
-
fn main() {}
diff --git a/src/tools/clippy/tests/ui/from_over_into_unfixable.stderr b/src/tools/clippy/tests/ui/from_over_into_unfixable.stderr
index bb966af4b0f..251f1d84e74 100644
--- a/src/tools/clippy/tests/ui/from_over_into_unfixable.stderr
+++ b/src/tools/clippy/tests/ui/from_over_into_unfixable.stderr
@@ -1,12 +1,29 @@
-error[E0658]: `impl Trait` in type aliases is unstable
- --> $DIR/from_over_into_unfixable.rs:35:15
+error: an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true
+ --> $DIR/from_over_into_unfixable.rs:11:1
|
-LL | type Opaque = impl Sized;
- | ^^^^^^^^^^
+LL | impl Into<InMacro> for String {
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
- = note: see issue #63063 <https://github.com/rust-lang/rust/issues/63063> for more information
- = help: add `#![feature(type_alias_impl_trait)]` to the crate attributes to enable
+ = help: replace the `Into` implementation with `From<std::string::String>`
+ = note: `-D clippy::from-over-into` implied by `-D warnings`
-error: aborting due to previous error
+error: an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true
+ --> $DIR/from_over_into_unfixable.rs:19:1
+ |
+LL | impl Into<WeirdUpperSelf> for &'static [u8] {
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+ = help: replace the `Into` implementation with `From<&'static [u8]>`
+
+error: an implementation of `From` is preferred since it gives you `Into<_>` for free where the reverse isn't true
+ --> $DIR/from_over_into_unfixable.rs:28:1
+ |
+LL | impl Into<u8> for ContainsVal {
+ | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+ |
+ = help: `impl From<Local> for Foreign` is allowed by the orphan rules, for more information see
+ https://doc.rust-lang.org/reference/items/implementations.html#trait-implementation-coherence
+ = help: replace the `Into` implementation with `From<ContainsVal>`
+
+error: aborting due to 3 previous errors
-For more information about this error, try `rustc --explain E0658`.
diff --git a/tests/ui/impl-trait/coherence-treats-tait-ambig.current.stderr b/tests/ui/impl-trait/coherence-treats-tait-ambig.current.stderr
new file mode 100644
index 00000000000..61fed16294b
--- /dev/null
+++ b/tests/ui/impl-trait/coherence-treats-tait-ambig.current.stderr
@@ -0,0 +1,13 @@
+error[E0119]: conflicting implementations of trait `Into<T>` for type `Foo`
+ --> $DIR/coherence-treats-tait-ambig.rs:10:1
+ |
+LL | impl Into<T> for Foo {
+ | ^^^^^^^^^^^^^^^^^^^^
+ |
+ = note: conflicting implementation in crate `core`:
+ - impl<T, U> Into<U> for T
+ where U: From<T>;
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0119`.
diff --git a/tests/ui/impl-trait/coherence-treats-tait-ambig.next.stderr b/tests/ui/impl-trait/coherence-treats-tait-ambig.next.stderr
new file mode 100644
index 00000000000..61fed16294b
--- /dev/null
+++ b/tests/ui/impl-trait/coherence-treats-tait-ambig.next.stderr
@@ -0,0 +1,13 @@
+error[E0119]: conflicting implementations of trait `Into<T>` for type `Foo`
+ --> $DIR/coherence-treats-tait-ambig.rs:10:1
+ |
+LL | impl Into<T> for Foo {
+ | ^^^^^^^^^^^^^^^^^^^^
+ |
+ = note: conflicting implementation in crate `core`:
+ - impl<T, U> Into<U> for T
+ where U: From<T>;
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0119`.
diff --git a/tests/ui/impl-trait/coherence-treats-tait-ambig.rs b/tests/ui/impl-trait/coherence-treats-tait-ambig.rs
new file mode 100644
index 00000000000..156a7eb0e23
--- /dev/null
+++ b/tests/ui/impl-trait/coherence-treats-tait-ambig.rs
@@ -0,0 +1,19 @@
+// revisions: current next
+//[next] compile-flags: -Ztrait-solver=next
+
+#![feature(type_alias_impl_trait)]
+
+type T = impl Sized;
+
+struct Foo;
+
+impl Into<T> for Foo {
+//~^ ERROR conflicting implementations of trait `Into<T>` for type `Foo`
+ fn into(self) -> T {
+ Foo
+ }
+}
+
+fn main() {
+ let _: T = Foo.into();
+}