Rollup merge of rust-lang#117133 - compiler-errors:coherence-constrained, r=oli-obk

Merge `impl_wf_inference` (`check_mod_impl_wf`) check into coherence checking

Problem here is that we call `collect_impl_trait_in_trait_types` when checking `check_mod_impl_wf` which is performed before coherence. Due to the `tcx.sess.track_errors`, since we end up reporting an error, we never actually proceed to coherence checking, where we would be emitting a more useful impl overlap error.

This change means that we may report more errors in some cases, but can at least proceed far enough to leave a useful message for overlapping traits with RPITITs in them.

Fixes rust-lang#116982

r? types

Author: matthiaskrgr

compiler/rustc_hir_analysis/src/lib.rs

@@ -181,14 +181,11 @@ pub fn check_crate(tcx: TyCtxt<'_>) -> Result<(), ErrorGuaranteed> {
         })?;
     }
 
-    tcx.sess.track_errors(|| {
-        tcx.sess.time("impl_wf_inference", || {
-            tcx.hir().for_each_module(|module| tcx.ensure().check_mod_impl_wf(module))
-        });
-    })?;
-
     tcx.sess.track_errors(|| {
         tcx.sess.time("coherence_checking", || {
+            // Check impls constrain their parameters
+            tcx.hir().for_each_module(|module| tcx.ensure().check_mod_impl_wf(module));
+
             for &trait_def_id in tcx.all_local_trait_impls(()).keys() {
                 tcx.ensure().coherent_trait(trait_def_id);
             }

tests/ui/async-await/in-trait/coherence-constrained.rs

@@ -0,0 +1,26 @@
+// edition: 2021
+
+trait Foo {
+    type T;
+
+    async fn foo(&self) -> Self::T;
+}
+
+struct Bar;
+
+impl Foo for Bar {
+    type T = ();
+
+    async fn foo(&self) {}
+    //~^ ERROR type annotations needed: cannot satisfy `<Bar as Foo>::T == ()`
+}
+
+impl Foo for Bar {
+    //~^ ERROR conflicting implementations of trait `Foo` for type `Bar`
+    type T = ();
+
+    async fn foo(&self) {}
+    //~^ ERROR type annotations needed: cannot satisfy `<Bar as Foo>::T == ()`
+}
+
+fn main() {}

tests/ui/async-await/in-trait/coherence-constrained.stderr

@@ -0,0 +1,25 @@
+error[E0284]: type annotations needed: cannot satisfy `<Bar as Foo>::T == ()`
+  --> $DIR/coherence-constrained.rs:14:5
+   |
+LL |     async fn foo(&self) {}
+   |     ^^^^^^^^^^^^^^^^^^^ cannot satisfy `<Bar as Foo>::T == ()`
+
+error[E0284]: type annotations needed: cannot satisfy `<Bar as Foo>::T == ()`
+  --> $DIR/coherence-constrained.rs:22:5
+   |
+LL |     async fn foo(&self) {}
+   |     ^^^^^^^^^^^^^^^^^^^ cannot satisfy `<Bar as Foo>::T == ()`
+
+error[E0119]: conflicting implementations of trait `Foo` for type `Bar`
+  --> $DIR/coherence-constrained.rs:18:1
+   |
+LL | impl Foo for Bar {
+   | ---------------- first implementation here
+...
+LL | impl Foo for Bar {
+   | ^^^^^^^^^^^^^^^^ conflicting implementation for `Bar`
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0119, E0284.
+For more information about an error, try `rustc --explain E0119`.

tests/ui/impl-unused-tps.rs

@@ -1,3 +1,5 @@
+//~ ERROR overflow evaluating the requirement `([isize; 0], _): Sized
+
 trait Foo<A> {
     fn get(&self, A: &A) { }
 }
@@ -23,8 +25,7 @@ impl<T:Bar<Out=U>,U> Foo<T> for [isize;3] {
 }
 
 impl<T,U> Foo<T> for U {
-    // OK, T, U are used everywhere. Note that the coherence check
-    // hasn't executed yet, so no errors about overlap.
+    //~^ ERROR conflicting implementations of trait `Foo<_>` for type `[isize; 0]`
 }
 
 impl<T,U> Bar for T {

tests/ui/impl-unused-tps.stderr

@@ -1,33 +1,56 @@
 error[E0207]: the type parameter `U` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/impl-unused-tps.rs:13:8
+  --> $DIR/impl-unused-tps.rs:15:8
    |
 LL | impl<T,U> Foo<T> for [isize;1] {
    |        ^ unconstrained type parameter
 
 error[E0207]: the type parameter `U` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/impl-unused-tps.rs:30:8
+  --> $DIR/impl-unused-tps.rs:31:8
    |
 LL | impl<T,U> Bar for T {
    |        ^ unconstrained type parameter
 
 error[E0207]: the type parameter `U` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/impl-unused-tps.rs:38:8
+  --> $DIR/impl-unused-tps.rs:39:8
    |
 LL | impl<T,U> Bar for T
    |        ^ unconstrained type parameter
 
 error[E0207]: the type parameter `U` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/impl-unused-tps.rs:46:8
+  --> $DIR/impl-unused-tps.rs:47:8
    |
 LL | impl<T,U,V> Foo<T> for T
    |        ^ unconstrained type parameter
 
 error[E0207]: the type parameter `V` is not constrained by the impl trait, self type, or predicates
-  --> $DIR/impl-unused-tps.rs:46:10
+  --> $DIR/impl-unused-tps.rs:47:10
    |
 LL | impl<T,U,V> Foo<T> for T
    |          ^ unconstrained type parameter
 
-error: aborting due to 5 previous errors
+error[E0119]: conflicting implementations of trait `Foo<_>` for type `[isize; 0]`
+  --> $DIR/impl-unused-tps.rs:27:1
+   |
+LL | impl<T> Foo<T> for [isize;0] {
+   | ---------------------------- first implementation here
+...
+LL | impl<T,U> Foo<T> for U {
+   | ^^^^^^^^^^^^^^^^^^^^^^ conflicting implementation for `[isize; 0]`
+
+error[E0275]: overflow evaluating the requirement `([isize; 0], _): Sized`
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`impl_unused_tps`)
+note: required for `([isize; 0], _)` to implement `Bar`
+  --> $DIR/impl-unused-tps.rs:31:11
+   |
+LL | impl<T,U> Bar for T {
+   |      -    ^^^     ^
+   |      |
+   |      unsatisfied trait bound introduced here
+   = note: 126 redundant requirements hidden
+   = note: required for `([isize; 0], _)` to implement `Bar`
+
+error: aborting due to 7 previous errors
 
-For more information about this error, try `rustc --explain E0207`.
+Some errors have detailed explanations: E0119, E0207, E0275.
+For more information about an error, try `rustc --explain E0119`.