Rollup merge of #87348 - SkiFire13:fix-87261, r=oli-obk

Fix span when suggesting to add an associated type bound

Fixes #87261

Note that this fix is not perfect, it ~~will still give incorrect~~ won't give suggestions in some situations:
- If the associated type is defined on a supertrait of those contained in the opaque type, it will fallback to the previous behaviour, e.g. if `AssocTy` is defined on the trait `Foo`, `Bar` has `Foo` as supertrait and the opaque type is a `impl Bar + Baz`.
- If the the associated type is defined on a generic trait and the opaque type includes two versions of that generic trait, e.g. the opaque type is `impl Foo<A> + Foo<B>`

2 files changed, 337 insertions, 0 deletions

diff --git a/src/test/ui/associated-types/issue-87261.rs b/src/test/ui/associated-types/issue-87261.rs
new file mode 100644
index 00000000000..a70f771e482
--- /dev/null
+++ b/src/test/ui/associated-types/issue-87261.rs
@@ -0,0 +1,99 @@
+trait Foo {}
+
+trait Trait {
+    type Associated;
+}
+trait DerivedTrait: Trait {}
+trait GenericTrait<A> {
+    type Associated;
+}
+
+struct Impl;
+impl Foo for Impl {}
+impl Trait for Impl {
+    type Associated = ();
+}
+impl DerivedTrait for Impl {}
+impl<A> GenericTrait<A> for Impl {
+    type Associated = ();
+}
+
+fn returns_opaque() -> impl Trait + 'static {
+    Impl
+}
+fn returns_opaque_derived() -> impl DerivedTrait + 'static {
+    Impl
+}
+fn returns_opaque_foo() -> impl Trait + Foo {
+    Impl
+}
+fn returns_opaque_derived_foo() -> impl DerivedTrait + Foo {
+    Impl
+}
+fn returns_opaque_generic() -> impl GenericTrait<()> + 'static {
+    Impl
+}
+fn returns_opaque_generic_foo() -> impl GenericTrait<()> + Foo {
+    Impl
+}
+fn returns_opaque_generic_duplicate() -> impl GenericTrait<()> + GenericTrait<u8> {
+    Impl
+}
+
+fn accepts_trait<T: Trait<Associated = ()>>(_: T) {}
+fn accepts_generic_trait<T: GenericTrait<(), Associated = ()>>(_: T) {}
+
+fn check_generics<A, B, C, D, E, F, G>(a: A, b: B, c: C, d: D, e: E, f: F, g: G)
+where
+    A: Trait + 'static,
+    B: DerivedTrait + 'static,
+    C: Trait + Foo,
+    D: DerivedTrait + Foo,
+    E: GenericTrait<()> + 'static,
+    F: GenericTrait<()> + Foo,
+    G: GenericTrait<()> + GenericTrait<u8>,
+{
+    accepts_trait(a);
+    //~^ ERROR type mismatch resolving `<A as Trait>::Associated == ()`
+
+    accepts_trait(b);
+    //~^ ERROR type mismatch resolving `<B as Trait>::Associated == ()`
+
+    accepts_trait(c);
+    //~^ ERROR type mismatch resolving `<C as Trait>::Associated == ()`
+
+    accepts_trait(d);
+    //~^ ERROR type mismatch resolving `<D as Trait>::Associated == ()`
+
+    accepts_generic_trait(e);
+    //~^ ERROR type mismatch resolving `<E as GenericTrait<()>>::Associated == ()`
+
+    accepts_generic_trait(f);
+    //~^ ERROR type mismatch resolving `<F as GenericTrait<()>>::Associated == ()`
+
+    accepts_generic_trait(g);
+    //~^ ERROR type mismatch resolving `<G as GenericTrait<()>>::Associated == ()`
+}
+
+fn main() {
+    accepts_trait(returns_opaque());
+    //~^ ERROR type mismatch resolving `<impl Trait as Trait>::Associated == ()`
+
+    accepts_trait(returns_opaque_derived());
+    //~^ ERROR type mismatch resolving `<impl DerivedTrait as Trait>::Associated == ()`
+
+    accepts_trait(returns_opaque_foo());
+    //~^ ERROR type mismatch resolving `<impl Trait+Foo as Trait>::Associated == ()`
+
+    accepts_trait(returns_opaque_derived_foo());
+    //~^ ERROR type mismatch resolving `<impl DerivedTrait+Foo as Trait>::Associated == ()`
+
+    accepts_generic_trait(returns_opaque_generic());
+    //~^ ERROR type mismatch resolving `<impl GenericTrait<()> as GenericTrait<()>>::Associated == ()`
+
+    accepts_generic_trait(returns_opaque_generic_foo());
+    //~^ ERROR type mismatch resolving `<impl GenericTrait<()>+Foo as GenericTrait<()>>::Associated == ()`
+
+    accepts_generic_trait(returns_opaque_generic_duplicate());
+    //~^ ERROR type mismatch resolving `<impl GenericTrait<()>+GenericTrait<u8> as GenericTrait<()>>::Associated == ()`
+}
diff --git a/src/test/ui/associated-types/issue-87261.stderr b/src/test/ui/associated-types/issue-87261.stderr
new file mode 100644
index 00000000000..0725acfe537
--- /dev/null
+++ b/src/test/ui/associated-types/issue-87261.stderr
@@ -0,0 +1,238 @@
+error[E0271]: type mismatch resolving `<A as Trait>::Associated == ()`
+  --> $DIR/issue-87261.rs:56:5
+   |
+LL | fn accepts_trait<T: Trait<Associated = ()>>(_: T) {}
+   |                           --------------- required by this bound in `accepts_trait`
+...
+LL |     accepts_trait(a);
+   |     ^^^^^^^^^^^^^ expected `()`, found associated type
+   |
+   = note:    expected unit type `()`
+           found associated type `<A as Trait>::Associated`
+help: consider constraining the associated type `<A as Trait>::Associated` to `()`
+   |
+LL |     A: Trait<Associated = ()> + 'static,
+   |             ^^^^^^^^^^^^^^^^^
+
+error[E0271]: type mismatch resolving `<B as Trait>::Associated == ()`
+  --> $DIR/issue-87261.rs:59:5
+   |
+LL | fn accepts_trait<T: Trait<Associated = ()>>(_: T) {}
+   |                           --------------- required by this bound in `accepts_trait`
+...
+LL |     accepts_trait(b);
+   |     ^^^^^^^^^^^^^ expected `()`, found associated type
+   |
+   = note:    expected unit type `()`
+           found associated type `<B as Trait>::Associated`
+   = help: consider constraining the associated type `<B as Trait>::Associated` to `()`
+   = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
+
+error[E0271]: type mismatch resolving `<C as Trait>::Associated == ()`
+  --> $DIR/issue-87261.rs:62:5
+   |
+LL | fn accepts_trait<T: Trait<Associated = ()>>(_: T) {}
+   |                           --------------- required by this bound in `accepts_trait`
+...
+LL |     accepts_trait(c);
+   |     ^^^^^^^^^^^^^ expected `()`, found associated type
+   |
+   = note:    expected unit type `()`
+           found associated type `<C as Trait>::Associated`
+help: consider constraining the associated type `<C as Trait>::Associated` to `()`
+   |
+LL |     C: Trait<Associated = ()> + Foo,
+   |             ^^^^^^^^^^^^^^^^^
+
+error[E0271]: type mismatch resolving `<D as Trait>::Associated == ()`
+  --> $DIR/issue-87261.rs:65:5
+   |
+LL | fn accepts_trait<T: Trait<Associated = ()>>(_: T) {}
+   |                           --------------- required by this bound in `accepts_trait`
+...
+LL |     accepts_trait(d);
+   |     ^^^^^^^^^^^^^ expected `()`, found associated type
+   |
+   = note:    expected unit type `()`
+           found associated type `<D as Trait>::Associated`
+   = help: consider constraining the associated type `<D as Trait>::Associated` to `()`
+   = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
+
+error[E0271]: type mismatch resolving `<E as GenericTrait<()>>::Associated == ()`
+  --> $DIR/issue-87261.rs:68:5
+   |
+LL | fn accepts_generic_trait<T: GenericTrait<(), Associated = ()>>(_: T) {}
+   |                                              --------------- required by this bound in `accepts_generic_trait`
+...
+LL |     accepts_generic_trait(e);
+   |     ^^^^^^^^^^^^^^^^^^^^^ expected `()`, found associated type
+   |
+   = note:    expected unit type `()`
+           found associated type `<E as GenericTrait<()>>::Associated`
+help: consider constraining the associated type `<E as GenericTrait<()>>::Associated` to `()`
+   |
+LL |     E: GenericTrait<(), Associated = ()> + 'static,
+   |                       ^^^^^^^^^^^^^^^^^
+
+error[E0271]: type mismatch resolving `<F as GenericTrait<()>>::Associated == ()`
+  --> $DIR/issue-87261.rs:71:5
+   |
+LL | fn accepts_generic_trait<T: GenericTrait<(), Associated = ()>>(_: T) {}
+   |                                              --------------- required by this bound in `accepts_generic_trait`
+...
+LL |     accepts_generic_trait(f);
+   |     ^^^^^^^^^^^^^^^^^^^^^ expected `()`, found associated type
+   |
+   = note:    expected unit type `()`
+           found associated type `<F as GenericTrait<()>>::Associated`
+help: consider constraining the associated type `<F as GenericTrait<()>>::Associated` to `()`
+   |
+LL |     F: GenericTrait<(), Associated = ()> + Foo,
+   |                       ^^^^^^^^^^^^^^^^^
+
+error[E0271]: type mismatch resolving `<G as GenericTrait<()>>::Associated == ()`
+  --> $DIR/issue-87261.rs:74:5
+   |
+LL | fn accepts_generic_trait<T: GenericTrait<(), Associated = ()>>(_: T) {}
+   |                                              --------------- required by this bound in `accepts_generic_trait`
+...
+LL |     accepts_generic_trait(g);
+   |     ^^^^^^^^^^^^^^^^^^^^^ expected `()`, found associated type
+   |
+   = note:    expected unit type `()`
+           found associated type `<G as GenericTrait<()>>::Associated`
+   = help: consider constraining the associated type `<G as GenericTrait<()>>::Associated` to `()`
+   = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
+
+error[E0271]: type mismatch resolving `<impl Trait as Trait>::Associated == ()`
+  --> $DIR/issue-87261.rs:79:5
+   |
+LL | fn returns_opaque() -> impl Trait + 'static {
+   |                        -------------------- the found opaque type
+...
+LL | fn accepts_trait<T: Trait<Associated = ()>>(_: T) {}
+   |                           --------------- required by this bound in `accepts_trait`
+...
+LL |     accepts_trait(returns_opaque());
+   |     ^^^^^^^^^^^^^ expected `()`, found associated type
+   |
+   = note:    expected unit type `()`
+           found associated type `<impl Trait as Trait>::Associated`
+help: consider constraining the associated type `<impl Trait as Trait>::Associated` to `()`
+   |
+LL | fn returns_opaque() -> impl Trait<Associated = ()> + 'static {
+   |                                  ^^^^^^^^^^^^^^^^^
+
+error[E0271]: type mismatch resolving `<impl DerivedTrait as Trait>::Associated == ()`
+  --> $DIR/issue-87261.rs:82:5
+   |
+LL | fn returns_opaque_derived() -> impl DerivedTrait + 'static {
+   |                                --------------------------- the found opaque type
+...
+LL | fn accepts_trait<T: Trait<Associated = ()>>(_: T) {}
+   |                           --------------- required by this bound in `accepts_trait`
+...
+LL |     accepts_trait(returns_opaque_derived());
+   |     ^^^^^^^^^^^^^ expected `()`, found associated type
+   |
+   = note:    expected unit type `()`
+           found associated type `<impl DerivedTrait as Trait>::Associated`
+help: consider constraining the associated type `<impl DerivedTrait as Trait>::Associated` to `()`
+   |
+LL | fn returns_opaque_derived() -> impl DerivedTrait<Associated = ()> + 'static {
+   |                                                 ^^^^^^^^^^^^^^^^^
+
+error[E0271]: type mismatch resolving `<impl Trait+Foo as Trait>::Associated == ()`
+  --> $DIR/issue-87261.rs:85:5
+   |
+LL | fn returns_opaque_foo() -> impl Trait + Foo {
+   |                            ---------------- the found opaque type
+...
+LL | fn accepts_trait<T: Trait<Associated = ()>>(_: T) {}
+   |                           --------------- required by this bound in `accepts_trait`
+...
+LL |     accepts_trait(returns_opaque_foo());
+   |     ^^^^^^^^^^^^^ expected `()`, found associated type
+   |
+   = note:    expected unit type `()`
+           found associated type `<impl Trait+Foo as Trait>::Associated`
+help: consider constraining the associated type `<impl Trait+Foo as Trait>::Associated` to `()`
+   |
+LL | fn returns_opaque_foo() -> impl Trait<Associated = ()> + Foo {
+   |                                      ^^^^^^^^^^^^^^^^^
+
+error[E0271]: type mismatch resolving `<impl DerivedTrait+Foo as Trait>::Associated == ()`
+  --> $DIR/issue-87261.rs:88:5
+   |
+LL | fn returns_opaque_derived_foo() -> impl DerivedTrait + Foo {
+   |                                    ----------------------- the found opaque type
+...
+LL | fn accepts_trait<T: Trait<Associated = ()>>(_: T) {}
+   |                           --------------- required by this bound in `accepts_trait`
+...
+LL |     accepts_trait(returns_opaque_derived_foo());
+   |     ^^^^^^^^^^^^^ expected `()`, found associated type
+   |
+   = note:    expected unit type `()`
+           found associated type `<impl DerivedTrait+Foo as Trait>::Associated`
+   = help: consider constraining the associated type `<impl DerivedTrait+Foo as Trait>::Associated` to `()`
+   = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
+
+error[E0271]: type mismatch resolving `<impl GenericTrait<()> as GenericTrait<()>>::Associated == ()`
+  --> $DIR/issue-87261.rs:91:5
+   |
+LL | fn returns_opaque_generic() -> impl GenericTrait<()> + 'static {
+   |                                ------------------------------- the found opaque type
+...
+LL | fn accepts_generic_trait<T: GenericTrait<(), Associated = ()>>(_: T) {}
+   |                                              --------------- required by this bound in `accepts_generic_trait`
+...
+LL |     accepts_generic_trait(returns_opaque_generic());
+   |     ^^^^^^^^^^^^^^^^^^^^^ expected `()`, found associated type
+   |
+   = note:    expected unit type `()`
+           found associated type `<impl GenericTrait<()> as GenericTrait<()>>::Associated`
+help: consider constraining the associated type `<impl GenericTrait<()> as GenericTrait<()>>::Associated` to `()`
+   |
+LL | fn returns_opaque_generic() -> impl GenericTrait<(), Associated = ()> + 'static {
+   |                                                    ^^^^^^^^^^^^^^^^^
+
+error[E0271]: type mismatch resolving `<impl GenericTrait<()>+Foo as GenericTrait<()>>::Associated == ()`
+  --> $DIR/issue-87261.rs:94:5
+   |
+LL | fn returns_opaque_generic_foo() -> impl GenericTrait<()> + Foo {
+   |                                    --------------------------- the found opaque type
+...
+LL | fn accepts_generic_trait<T: GenericTrait<(), Associated = ()>>(_: T) {}
+   |                                              --------------- required by this bound in `accepts_generic_trait`
+...
+LL |     accepts_generic_trait(returns_opaque_generic_foo());
+   |     ^^^^^^^^^^^^^^^^^^^^^ expected `()`, found associated type
+   |
+   = note:    expected unit type `()`
+           found associated type `<impl GenericTrait<()>+Foo as GenericTrait<()>>::Associated`
+help: consider constraining the associated type `<impl GenericTrait<()>+Foo as GenericTrait<()>>::Associated` to `()`
+   |
+LL | fn returns_opaque_generic_foo() -> impl GenericTrait<(), Associated = ()> + Foo {
+   |                                                        ^^^^^^^^^^^^^^^^^
+
+error[E0271]: type mismatch resolving `<impl GenericTrait<()>+GenericTrait<u8> as GenericTrait<()>>::Associated == ()`
+  --> $DIR/issue-87261.rs:97:5
+   |
+LL | fn returns_opaque_generic_duplicate() -> impl GenericTrait<()> + GenericTrait<u8> {
+   |                                          ---------------------------------------- the found opaque type
+...
+LL | fn accepts_generic_trait<T: GenericTrait<(), Associated = ()>>(_: T) {}
+   |                                              --------------- required by this bound in `accepts_generic_trait`
+...
+LL |     accepts_generic_trait(returns_opaque_generic_duplicate());
+   |     ^^^^^^^^^^^^^^^^^^^^^ expected `()`, found associated type
+   |
+   = note:    expected unit type `()`
+           found associated type `<impl GenericTrait<()>+GenericTrait<u8> as GenericTrait<()>>::Associated`
+   = help: consider constraining the associated type `<impl GenericTrait<()>+GenericTrait<u8> as GenericTrait<()>>::Associated` to `()`
+   = note: for more information, visit https://doc.rust-lang.org/book/ch19-03-advanced-traits.html
+
+error: aborting due to 14 previous errors
+
+For more information about this error, try `rustc --explain E0271`.