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Rollup merge of rust-lang#133428 - compiler-errors:rpitit-unsound, r=…
…lcnr Actually use placeholder regions for trait method late bound regions in `collect_return_position_impl_trait_in_trait_tys` So in rust-lang#113182, I introduced a "diagnostics improvement" in the form of 473c88d, which changes which signature we end up instantiating with placeholder regions and which signature we end up instantiating with fresh region vars so that we have placeholders corresponding to the names of the late-bound regions coming from the *impl*. However, this is not sound, since now we're essentially no longer proving that *all* instantiations of the trait method are compatible with an instantiation of the impl method, but vice versa (which is weaker). Let's look at the example `tests/ui/impl-trait/in-trait/do-not-imply-from-trait-impl.rs`: ```rust trait MkStatic { fn mk_static(self) -> &'static str; } impl MkStatic for &'static str { fn mk_static(self) -> &'static str { self } } trait Foo { fn foo<'a: 'static, 'late>(&'late self) -> impl MkStatic; } impl Foo for str { fn foo<'a: 'static>(&'a self) -> impl MkStatic + 'static { self } } fn call_foo<T: Foo + ?Sized>(t: &T) -> &'static str { t.foo().mk_static() } fn main() { let s = call_foo(String::from("hello, world").as_str()); println!("> {s}"); } ``` To collect RPITITs, we were previously instantiating the trait signature with infer vars (`fn(&'?0 str) -> ?1t` where `?1t` is the variable we use to infer the RPITIT) and the impl signature with placeholders (there are no late-bound regions in that signature, so we just have `fn(&'a str) -> Opaque`). Equating the signatures works, since all we do is unify `?1t` with `Opaque` and `'?0` with `'a`. However, conceptually it *shouldn't* hold, since this definition is not valid for *all* instantiations of the trait method but just the one where `'0` (i.e. `'late`) is equal to `'a` :( ## So what This PR effectively reverts 473c88d to fix the unsoundness. Fixes rust-lang#133427 Also fixes rust-lang#133425, which is actually coincidentally another instance of this bug (but not one that is weaponized into UB, just one that causes an ICE in refinement checking).
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30 changes: 30 additions & 0 deletions
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tests/ui/impl-trait/in-trait/do-not-imply-from-trait-impl.rs
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// Make sure that we don't accidentally collect an RPITIT hidden type that does not | ||
// hold for all instantiations of the trait signature. | ||
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trait MkStatic { | ||
fn mk_static(self) -> &'static str; | ||
} | ||
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impl MkStatic for &'static str { | ||
fn mk_static(self) -> &'static str { self } | ||
} | ||
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trait Foo { | ||
fn foo<'a: 'static, 'late>(&'late self) -> impl MkStatic; | ||
} | ||
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impl Foo for str { | ||
fn foo<'a: 'static>(&'a self) -> impl MkStatic + 'static { | ||
//~^ ERROR method not compatible with trait | ||
self | ||
} | ||
} | ||
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fn call_foo<T: Foo + ?Sized>(t: &T) -> &'static str { | ||
t.foo().mk_static() | ||
} | ||
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fn main() { | ||
let s = call_foo(String::from("hello, world").as_str()); | ||
println!("> {s}"); | ||
} |
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tests/ui/impl-trait/in-trait/do-not-imply-from-trait-impl.stderr
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error[E0308]: method not compatible with trait | ||
--> $DIR/do-not-imply-from-trait-impl.rs:17:38 | ||
| | ||
LL | fn foo<'a: 'static>(&'a self) -> impl MkStatic + 'static { | ||
| ^^^^^^^^^^^^^^^^^^^^^^^ lifetime mismatch | ||
| | ||
= note: expected signature `fn(&'late _) -> _` | ||
found signature `fn(&'a _) -> _` | ||
note: the lifetime `'late` as defined here... | ||
--> $DIR/do-not-imply-from-trait-impl.rs:13:25 | ||
| | ||
LL | fn foo<'a: 'static, 'late>(&'late self) -> impl MkStatic; | ||
| ^^^^^ | ||
note: ...does not necessarily outlive the lifetime `'a` as defined here | ||
--> $DIR/do-not-imply-from-trait-impl.rs:17:12 | ||
| | ||
LL | fn foo<'a: 'static>(&'a self) -> impl MkStatic + 'static { | ||
| ^^ | ||
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error: aborting due to 1 previous error | ||
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For more information about this error, try `rustc --explain E0308`. |
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15 changes: 8 additions & 7 deletions
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tests/ui/impl-trait/in-trait/signature-mismatch.failure.stderr
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error[E0623]: lifetime mismatch | ||
error[E0477]: the type `impl Future<Output = Vec<u8>>` does not fulfill the required lifetime | ||
--> $DIR/signature-mismatch.rs:77:10 | ||
| | ||
LL | &'a self, | ||
| -------- this parameter and the return type are declared with different lifetimes... | ||
... | ||
LL | ) -> impl Future<Output = Vec<u8>> { | ||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | ||
| | | ||
| ...but data from `buff` is returned here | ||
| | ||
note: type must outlive the lifetime `'a` as defined here as required by this binding | ||
--> $DIR/signature-mismatch.rs:73:32 | ||
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LL | fn async_fn_reduce_outlive<'a, 'b, T>( | ||
| ^^ | ||
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error: aborting due to 1 previous error | ||
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For more information about this error, try `rustc --explain E0623`. | ||
For more information about this error, try `rustc --explain E0477`. |
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7 changes: 4 additions & 3 deletions
7
tests/ui/impl-trait/precise-capturing/rpitit-impl-captures-too-much.stderr
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