Do not use global cache for selection candidates if opaque types can be constrained

Author: oli-obk

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -49,6 +49,7 @@ use rustc_middle::ty::{self, PolyProjectionPredicate, Upcast};
 use rustc_middle::ty::{Ty, TyCtxt, TypeFoldable, TypeVisitableExt};
 use rustc_span::symbol::sym;
 use rustc_span::Symbol;
+use rustc_type_ir::InferCtxtLike as _;
 
 use std::cell::{Cell, RefCell};
 use std::cmp;
@@ -1557,6 +1558,13 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         if self.is_intercrate() {
             return None;
         }
+
+        // Opaque types are not part of the global cache key, so we'd be caching and loading
+        // values, even though we don't have all the information that went into them.
+        if !self.infcx.defining_opaque_types().is_empty() {
+            return None;
+        }
+
         let tcx = self.tcx();
         let pred = cache_fresh_trait_pred.skip_binder();
 
@@ -1595,6 +1603,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         if self.is_intercrate() {
             return false;
         }
+        // Opaque types are not part of the global cache key, so we'd be caching and loading
+        // values, even though we don't have all the information that went into them.
+        if !self.infcx.defining_opaque_types().is_empty() {
+            return false;
+        }
         match result {
             Ok(Some(SelectionCandidate::ParamCandidate(trait_ref))) => !trait_ref.has_infer(),
             _ => true,

tests/ui/coherence/occurs-check/opaques.next.stderr

@@ -1,5 +1,5 @@
 error[E0119]: conflicting implementations of trait `Trait<_>`
-  --> $DIR/opaques.rs:30:1
+  --> $DIR/opaques.rs:28:1
    |
 LL | impl<T> Trait<T> for T {
    | ---------------------- first implementation here
@@ -8,7 +8,7 @@ LL | impl<T> Trait<T> for defining_scope::Alias<T> {
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation
 
 error[E0282]: type annotations needed
-  --> $DIR/opaques.rs:13:20
+  --> $DIR/opaques.rs:11:20
    |
 LL |     pub fn cast<T>(x: Container<Alias<T>, T>) -> Container<T, T> {
    |                    ^ cannot infer type

tests/ui/coherence/occurs-check/opaques.old.stderr

@@ -0,0 +1,21 @@
+error[E0284]: type annotations needed
+  --> $DIR/opaques.rs:11:20
+   |
+LL |     pub fn cast<T>(x: Container<Alias<T>, T>) -> Container<T, T> {
+   |                    ^ cannot infer type
+   |
+   = note: cannot satisfy `<Alias<T> as Trait<T>>::Assoc == _`
+note: required because it appears within the type `Container<Alias<T>, T>`
+  --> $DIR/opaques.rs:17:8
+   |
+LL | struct Container<T: Trait<U>, U> {
+   |        ^^^^^^^^^
+   = help: unsized fn params are gated as an unstable feature
+help: function arguments must have a statically known size, borrowed types always have a known size
+   |
+LL |     pub fn cast<T>(x: &Container<Alias<T>, T>) -> Container<T, T> {
+   |                       +
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0284`.

tests/ui/coherence/occurs-check/opaques.rs

@@ -3,15 +3,13 @@
 
 // A regression test for #105787
 
-//@[old] known-bug: #105787
-//@[old] check-pass
 #![feature(type_alias_impl_trait)]
 mod defining_scope {
     use super::*;
     pub type Alias<T> = impl Sized;
 
     pub fn cast<T>(x: Container<Alias<T>, T>) -> Container<T, T> {
-        //[next]~^ ERROR type annotations needed
+        //~^ ERROR type annotations needed
         x
     }
 }

tests/ui/impl-trait/equality.rs

@@ -22,7 +22,7 @@ fn sum_to(n: u32) -> impl Foo {
         0
     } else {
         n + sum_to(n - 1)
-        //~^ ERROR cannot satisfy `<u32 as Add<impl Foo>>::Output == i32`
+        //~^ ERROR cannot satisfy `<u32 as Add<impl Foo>>::Output == u32`
     }
 }
 

tests/ui/impl-trait/equality.stderr

@@ -22,11 +22,11 @@ help: change the type of the numeric literal from `u32` to `i32`
 LL |     0_i32
    |       ~~~
 
-error[E0284]: type annotations needed: cannot satisfy `<u32 as Add<impl Foo>>::Output == i32`
+error[E0284]: type annotations needed: cannot satisfy `<u32 as Add<impl Foo>>::Output == u32`
   --> $DIR/equality.rs:24:11
    |
 LL |         n + sum_to(n - 1)
-   |           ^ cannot satisfy `<u32 as Add<impl Foo>>::Output == i32`
+   |           ^ cannot satisfy `<u32 as Add<impl Foo>>::Output == u32`
 
 error: aborting due to 2 previous errors; 1 warning emitted
 

tests/ui/type-alias-impl-trait/escaping-bound-var.rs

@@ -8,6 +8,7 @@ trait Test<'a> {}
 
 pub type Foo = impl for<'a> Trait<'a, Assoc = impl Test<'a>>;
 //~^ ERROR `impl Trait` cannot capture higher-ranked lifetime from outer `impl Trait`
+//~| ERROR unconstrained opaque type
 
 impl Trait<'_> for () {
     type Assoc = ();

tests/ui/type-alias-impl-trait/escaping-bound-var.stderr

@@ -10,6 +10,14 @@ note: lifetime declared here
 LL | pub type Foo = impl for<'a> Trait<'a, Assoc = impl Test<'a>>;
    |                         ^^
 
-error: aborting due to 1 previous error
+error: unconstrained opaque type
+  --> $DIR/escaping-bound-var.rs:9:47
+   |
+LL | pub type Foo = impl for<'a> Trait<'a, Assoc = impl Test<'a>>;
+   |                                               ^^^^^^^^^^^^^
+   |
+   = note: `Foo` must be used in combination with a concrete type within the same module
+
+error: aborting due to 2 previous errors
 
 For more information about this error, try `rustc --explain E0657`.