Auto merge of #119744 - lcnr:assemble-only-rigid, r=compiler-errors

only assemble alias bound candidates for rigid aliases

fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/77

This also causes `<Wrapper<?0> as Trait>::Unwrap: Trait` to always be ambig, as we now normalize the self type before checking whether it is an inference variable.

I cannot think of an approach to the underlying issues here which does not require the "may-define means must-define" restriction for opaque types. Going to go ahead with this and added this restriction to the tracking issue for the new solver to make sure we don't stabilize it without getting types + lang signoff here.

r? `@compiler-errors`

11 files changed, 98 insertions, 22 deletions

diff --git a/tests/ui/traits/next-solver/alias-bound-unsound.rs b/tests/ui/traits/next-solver/alias-bound-unsound.rs
index 8fddbd7ecdc..633f0e75572 100644
--- a/tests/ui/traits/next-solver/alias-bound-unsound.rs
+++ b/tests/ui/traits/next-solver/alias-bound-unsound.rs
@@ -16,7 +16,7 @@ trait Foo {
 
 impl Foo for () {
     type Item = String where String: Copy;
-    //~^ ERROR overflow evaluating the requirement `<() as Foo>::Item: Copy`
+    //~^ ERROR overflow evaluating the requirement `String: Copy`
 }
 
 fn main() {
diff --git a/tests/ui/traits/next-solver/alias-bound-unsound.stderr b/tests/ui/traits/next-solver/alias-bound-unsound.stderr
index 874644317eb..d5f7e975b13 100644
--- a/tests/ui/traits/next-solver/alias-bound-unsound.stderr
+++ b/tests/ui/traits/next-solver/alias-bound-unsound.stderr
@@ -1,15 +1,17 @@
-error[E0275]: overflow evaluating the requirement `<() as Foo>::Item: Copy`
-  --> $DIR/alias-bound-unsound.rs:18:17
+error[E0275]: overflow evaluating the requirement `String: Copy`
+  --> $DIR/alias-bound-unsound.rs:18:38
    |
 LL |     type Item = String where String: Copy;
-   |                 ^^^^^^
+   |                                      ^^^^
    |
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`alias_bound_unsound`)
-note: required by a bound in `Foo::Item`
-  --> $DIR/alias-bound-unsound.rs:8:16
+note: the requirement `String: Copy` appears on the `impl`'s associated type `Item` but not on the corresponding trait's associated type
+  --> $DIR/alias-bound-unsound.rs:8:10
    |
+LL | trait Foo {
+   |       --- in this trait
 LL |     type Item: Copy
-   |                ^^^^ required by this bound in `Foo::Item`
+   |          ^^^^ this trait's associated type doesn't have the requirement `String: Copy`
 
 error[E0275]: overflow evaluating the requirement `String <: <() as Foo>::Item`
   --> $DIR/alias-bound-unsound.rs:24:31
diff --git a/tests/ui/traits/next-solver/assembly/ambig-projection-self-is-ambig.rs b/tests/ui/traits/next-solver/assembly/ambig-projection-self-is-ambig.rs
new file mode 100644
index 00000000000..99a368a746f
--- /dev/null
+++ b/tests/ui/traits/next-solver/assembly/ambig-projection-self-is-ambig.rs
@@ -0,0 +1,19 @@
+// check-pass
+// compile-flags: -Znext-solver
+
+trait Reader: Default {
+    fn read_u8_array<A>(&self) -> Result<A, ()> {
+        todo!()
+    }
+
+    fn read_u8(&self) -> Result<u8, ()> {
+        let a: [u8; 1] = self.read_u8_array::<_>()?;
+        // This results in a nested `<Result<?0, ()> as Try>::Residual: Sized` goal.
+        // The self type normalizes to `?0`. We previously did not force that to be
+        // ambiguous but instead incompletely applied the `Self: Sized` candidate
+        // from the `ParamEnv`, resulting in a type error.
+        Ok(a[0])
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/traits/next-solver/dont-type_of-tait-in-defining-scope.is_send.stderr b/tests/ui/traits/next-solver/dont-type_of-tait-in-defining-scope.is_send.stderr
new file mode 100644
index 00000000000..bafc4ba18a7
--- /dev/null
+++ b/tests/ui/traits/next-solver/dont-type_of-tait-in-defining-scope.is_send.stderr
@@ -0,0 +1,16 @@
+error[E0283]: type annotations needed: cannot satisfy `Foo: Send`
+  --> $DIR/dont-type_of-tait-in-defining-scope.rs:15:18
+   |
+LL |     needs_send::<Foo>();
+   |                  ^^^
+   |
+   = note: cannot satisfy `Foo: Send`
+note: required by a bound in `needs_send`
+  --> $DIR/dont-type_of-tait-in-defining-scope.rs:12:18
+   |
+LL | fn needs_send<T: Send>() {}
+   |                  ^^^^ required by this bound in `needs_send`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0283`.
diff --git a/tests/ui/traits/next-solver/dont-type_of-tait-in-defining-scope.not_send.stderr b/tests/ui/traits/next-solver/dont-type_of-tait-in-defining-scope.not_send.stderr
index 076dab29d89..bafc4ba18a7 100644
--- a/tests/ui/traits/next-solver/dont-type_of-tait-in-defining-scope.not_send.stderr
+++ b/tests/ui/traits/next-solver/dont-type_of-tait-in-defining-scope.not_send.stderr
@@ -1,12 +1,12 @@
 error[E0283]: type annotations needed: cannot satisfy `Foo: Send`
-  --> $DIR/dont-type_of-tait-in-defining-scope.rs:16:18
+  --> $DIR/dont-type_of-tait-in-defining-scope.rs:15:18
    |
 LL |     needs_send::<Foo>();
    |                  ^^^
    |
    = note: cannot satisfy `Foo: Send`
 note: required by a bound in `needs_send`
-  --> $DIR/dont-type_of-tait-in-defining-scope.rs:13:18
+  --> $DIR/dont-type_of-tait-in-defining-scope.rs:12:18
    |
 LL | fn needs_send<T: Send>() {}
    |                  ^^^^ required by this bound in `needs_send`
diff --git a/tests/ui/traits/next-solver/dont-type_of-tait-in-defining-scope.rs b/tests/ui/traits/next-solver/dont-type_of-tait-in-defining-scope.rs
index a1f38e69e53..ef0360248b5 100644
--- a/tests/ui/traits/next-solver/dont-type_of-tait-in-defining-scope.rs
+++ b/tests/ui/traits/next-solver/dont-type_of-tait-in-defining-scope.rs
@@ -1,6 +1,5 @@
 // revisions: is_send not_send
 // compile-flags: -Znext-solver
-//[is_send] check-pass
 
 #![feature(type_alias_impl_trait)]
 
@@ -14,7 +13,7 @@ fn needs_send<T: Send>() {}
 
 fn test(_: Foo) {
     needs_send::<Foo>();
-    //[not_send]~^ ERROR type annotations needed: cannot satisfy `Foo: Send`
+    //~^ ERROR type annotations needed: cannot satisfy `Foo: Send`
 }
 
 fn defines(_: Foo) {
diff --git a/tests/ui/traits/next-solver/overflow/recursive-self-normalization-2.rs b/tests/ui/traits/next-solver/overflow/recursive-self-normalization-2.rs
index 932826519b7..983a0fec653 100644
--- a/tests/ui/traits/next-solver/overflow/recursive-self-normalization-2.rs
+++ b/tests/ui/traits/next-solver/overflow/recursive-self-normalization-2.rs
@@ -17,6 +17,7 @@ fn test<T: Foo1<Assoc1 = <T as Foo2>::Assoc2> + Foo2<Assoc2 = <T as Foo1>::Assoc
     //~| ERROR overflow evaluating the requirement `<T as Foo1>::Assoc1 == _`
     //~| ERROR overflow evaluating the requirement `<T as Foo1>::Assoc1 == _`
     //~| ERROR overflow evaluating the requirement `<T as Foo1>::Assoc1 == _`
+    //~| ERROR overflow evaluating the requirement `<T as Foo1>::Assoc1: Sized`
     //~| ERROR overflow evaluating the requirement `<T as Foo1>::Assoc1: Bar`
 }
 
diff --git a/tests/ui/traits/next-solver/overflow/recursive-self-normalization-2.stderr b/tests/ui/traits/next-solver/overflow/recursive-self-normalization-2.stderr
index e4f1f9cf022..ed87404d573 100644
--- a/tests/ui/traits/next-solver/overflow/recursive-self-normalization-2.stderr
+++ b/tests/ui/traits/next-solver/overflow/recursive-self-normalization-2.stderr
@@ -19,6 +19,23 @@ note: required by a bound in `needs_bar`
 LL | fn needs_bar<S: Bar>() {}
    |                 ^^^ required by this bound in `needs_bar`
 
+error[E0275]: overflow evaluating the requirement `<T as Foo1>::Assoc1: Sized`
+  --> $DIR/recursive-self-normalization-2.rs:15:17
+   |
+LL |     needs_bar::<T::Assoc1>();
+   |                 ^^^^^^^^^
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`recursive_self_normalization_2`)
+note: required by a bound in `needs_bar`
+  --> $DIR/recursive-self-normalization-2.rs:12:14
+   |
+LL | fn needs_bar<S: Bar>() {}
+   |              ^ required by this bound in `needs_bar`
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL | fn needs_bar<S: Bar + ?Sized>() {}
+   |                     ++++++++
+
 error[E0275]: overflow evaluating the requirement `<T as Foo1>::Assoc1 == _`
   --> $DIR/recursive-self-normalization-2.rs:15:5
    |
@@ -45,6 +62,6 @@ LL |     needs_bar::<T::Assoc1>();
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`recursive_self_normalization_2`)
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error: aborting due to 5 previous errors
+error: aborting due to 6 previous errors
 
 For more information about this error, try `rustc --explain E0275`.
diff --git a/tests/ui/traits/next-solver/overflow/recursive-self-normalization.rs b/tests/ui/traits/next-solver/overflow/recursive-self-normalization.rs
index 32672c08c7e..40e2aa9e63f 100644
--- a/tests/ui/traits/next-solver/overflow/recursive-self-normalization.rs
+++ b/tests/ui/traits/next-solver/overflow/recursive-self-normalization.rs
@@ -13,6 +13,7 @@ fn test<T: Foo<Assoc = <T as Foo>::Assoc>>() {
     //~| ERROR overflow evaluating the requirement `<T as Foo>::Assoc == _`
     //~| ERROR overflow evaluating the requirement `<T as Foo>::Assoc == _`
     //~| ERROR overflow evaluating the requirement `<T as Foo>::Assoc == _`
+    //~| ERROR overflow evaluating the requirement `<T as Foo>::Assoc: Sized`
     //~| ERROR overflow evaluating the requirement `<T as Foo>::Assoc: Bar`
 }
 
diff --git a/tests/ui/traits/next-solver/overflow/recursive-self-normalization.stderr b/tests/ui/traits/next-solver/overflow/recursive-self-normalization.stderr
index da5c8bde568..e4ef2f60740 100644
--- a/tests/ui/traits/next-solver/overflow/recursive-self-normalization.stderr
+++ b/tests/ui/traits/next-solver/overflow/recursive-self-normalization.stderr
@@ -19,6 +19,23 @@ note: required by a bound in `needs_bar`
 LL | fn needs_bar<S: Bar>() {}
    |                 ^^^ required by this bound in `needs_bar`
 
+error[E0275]: overflow evaluating the requirement `<T as Foo>::Assoc: Sized`
+  --> $DIR/recursive-self-normalization.rs:11:17
+   |
+LL |     needs_bar::<T::Assoc>();
+   |                 ^^^^^^^^
+   |
+   = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`recursive_self_normalization`)
+note: required by a bound in `needs_bar`
+  --> $DIR/recursive-self-normalization.rs:8:14
+   |
+LL | fn needs_bar<S: Bar>() {}
+   |              ^ required by this bound in `needs_bar`
+help: consider relaxing the implicit `Sized` restriction
+   |
+LL | fn needs_bar<S: Bar + ?Sized>() {}
+   |                     ++++++++
+
 error[E0275]: overflow evaluating the requirement `<T as Foo>::Assoc == _`
   --> $DIR/recursive-self-normalization.rs:11:5
    |
@@ -45,6 +62,6 @@ LL |     needs_bar::<T::Assoc>();
    = help: consider increasing the recursion limit by adding a `#![recursion_limit = "256"]` attribute to your crate (`recursive_self_normalization`)
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
-error: aborting due to 5 previous errors
+error: aborting due to 6 previous errors
 
 For more information about this error, try `rustc --explain E0275`.
diff --git a/tests/ui/type-alias-impl-trait/issue-76202-trait-impl-for-tait.rs b/tests/ui/type-alias-impl-trait/issue-76202-trait-impl-for-tait.rs
index af1c18bbb59..b6906f68ded 100644
--- a/tests/ui/type-alias-impl-trait/issue-76202-trait-impl-for-tait.rs
+++ b/tests/ui/type-alias-impl-trait/issue-76202-trait-impl-for-tait.rs
@@ -4,20 +4,14 @@
 // revisions: current next
 //[next] compile-flags: -Znext-solver
 // check-pass
-
 #![feature(type_alias_impl_trait)]
 
-trait Dummy {}
-impl Dummy for () {}
-
-type F = impl Dummy;
-fn f() -> F {}
-
 trait Test {
     fn test(self);
 }
 
-impl Test for F {
+
+impl Test for define::F {
     fn test(self) {}
 }
 
@@ -27,7 +21,17 @@ impl Test for i32 {
     fn test(self) {}
 }
 
+mod define {
+    use super::*;
+
+    pub trait Dummy {}
+    impl Dummy for () {}
+
+    pub type F = impl Dummy;
+    pub fn f() -> F {}
+}
+
 fn main() {
-    let x: F = f();
+    let x = define::f();
     x.test();
 }