Rollup merge of #120378 - lcnr:normalize-ast, r=compiler-errors

always normalize `LoweredTy` in the new solver

I currently expect us to stop using alias bound candidates of normalizable aliases due to https://github.com/rust-lang/trait-system-refactor-initiative/issues/77 by landing https://github.com/rust-lang/rust/pull/119744. At this point it mostly doesn't matter whether we eagerly normalize (and replace with infer vars in case of ambiguity). cc #113473 previous attempt

The infer var replacement for ambiguous projections can in very rare cases:
- weaken inference https://github.com/rust-lang/trait-system-refactor-initiative/issues/81
- strengthen inference https://github.com/rust-lang/trait-system-refactor-initiative/issues/7

I do not expect this impact on inference to significantly affect real crates.

r? ``@compiler-errors``

compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs

@@ -369,6 +369,14 @@ pub struct LoweredTy<'tcx> {
 
 impl<'tcx> LoweredTy<'tcx> {
     pub fn from_raw(fcx: &FnCtxt<'_, 'tcx>, span: Span, raw: Ty<'tcx>) -> LoweredTy<'tcx> {
-        LoweredTy { raw, normalized: fcx.normalize(span, raw) }
+        // FIXME(-Znext-solver): We're still figuring out how to best handle
+        // normalization and this doesn't feel too great. We should look at this
+        // code again before stabilizing it.
+        let normalized = if fcx.next_trait_solver() {
+            fcx.try_structurally_resolve_type(span, raw)
+        } else {
+            fcx.normalize(span, raw)
+        };
+        LoweredTy { raw, normalized }
     }
 }

tests/ui/for/issue-20605.next.stderr

@@ -34,15 +34,11 @@ error: the type `&mut <dyn Iterator<Item = &'a mut u8> as IntoIterator>::IntoIte
 LL |     for item in *things { *item = 0 }
    |                 ^^^^^^^
 
-error[E0277]: the size for values of type `<<dyn Iterator<Item = &'a mut u8> as IntoIterator>::IntoIter as Iterator>::Item` cannot be known at compilation time
-  --> $DIR/issue-20605.rs:5:9
+error: the type `Option<<<dyn Iterator<Item = &'a mut u8> as IntoIterator>::IntoIter as Iterator>::Item>` is not well-formed
+  --> $DIR/issue-20605.rs:5:17
    |
 LL |     for item in *things { *item = 0 }
-   |         ^^^^ doesn't have a size known at compile-time
-   |
-   = help: the trait `Sized` is not implemented for `<<dyn Iterator<Item = &'a mut u8> as IntoIterator>::IntoIter as Iterator>::Item`
-   = note: all local variables must have a statically known size
-   = help: unsized locals are gated as an unstable feature
+   |                 ^^^^^^^
 
 error[E0277]: the size for values of type `<<dyn Iterator<Item = &'a mut u8> as IntoIterator>::IntoIter as Iterator>::Item` cannot be known at compilation time
   --> $DIR/issue-20605.rs:5:5
@@ -54,11 +50,15 @@ LL |     for item in *things { *item = 0 }
 note: required by a bound in `None`
   --> $SRC_DIR/core/src/option.rs:LL:COL
 
-error: the type `Option<<<dyn Iterator<Item = &'a mut u8> as IntoIterator>::IntoIter as Iterator>::Item>` is not well-formed
-  --> $DIR/issue-20605.rs:5:17
+error[E0277]: the size for values of type `<<dyn Iterator<Item = &'a mut u8> as IntoIterator>::IntoIter as Iterator>::Item` cannot be known at compilation time
+  --> $DIR/issue-20605.rs:5:9
    |
 LL |     for item in *things { *item = 0 }
-   |                 ^^^^^^^
+   |         ^^^^ doesn't have a size known at compile-time
+   |
+   = help: the trait `Sized` is not implemented for `<<dyn Iterator<Item = &'a mut u8> as IntoIterator>::IntoIter as Iterator>::Item`
+   = note: all local variables must have a statically known size
+   = help: unsized locals are gated as an unstable feature
 
 error[E0614]: type `<<dyn Iterator<Item = &'a mut u8> as IntoIterator>::IntoIter as Iterator>::Item` cannot be dereferenced
   --> $DIR/issue-20605.rs:5:27

tests/ui/traits/next-solver/alias-relate/tait-eq-proj-2.rs

@@ -3,7 +3,7 @@
 
 #![feature(type_alias_impl_trait)]
 
-// Similar to tests/ui/traits/next-solver/tait-eq-proj.rs
+// Similar to tests/ui/traits/next-solver/alias-relate/tait-eq-proj.rs
 // but check the alias-sub relation in the other direction.
 
 type Tait = impl Iterator<Item = impl Sized>;

tests/ui/traits/next-solver/normalize-path-for-method.rs

@@ -0,0 +1,18 @@
+// compile-flags: -Znext-solver
+// check-pass
+
+trait Mirror {
+    type Assoc;
+}
+impl<T> Mirror for T {
+    type Assoc = T;
+}
+
+struct Foo;
+impl Foo {
+    fn new() -> Self { Foo }
+}
+
+fn main() {
+    <Foo as Mirror>::Assoc::new();
+}

tests/ui/traits/next-solver/overflow/recursive-self-normalization-2.rs

@@ -16,6 +16,7 @@ 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 == _`
     //~| ERROR overflow evaluating the requirement `<T as Foo1>::Assoc1: Bar`
 }
 

tests/ui/traits/next-solver/overflow/recursive-self-normalization-2.stderr

@@ -1,3 +1,11 @@
+error[E0275]: overflow evaluating the requirement `<T as Foo1>::Assoc1 == _`
+  --> $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`)
+
 error[E0275]: overflow evaluating the requirement `<T as Foo1>::Assoc1: Bar`
   --> $DIR/recursive-self-normalization-2.rs:15:17
    |
@@ -35,7 +43,8 @@ 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 4 previous errors
+error: aborting due to 5 previous errors
 
 For more information about this error, try `rustc --explain E0275`.

tests/ui/traits/next-solver/overflow/recursive-self-normalization.rs

@@ -12,6 +12,7 @@ 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 == _`
     //~| ERROR overflow evaluating the requirement `<T as Foo>::Assoc: Bar`
 }
 

tests/ui/traits/next-solver/overflow/recursive-self-normalization.stderr

@@ -1,3 +1,11 @@
+error[E0275]: overflow evaluating the requirement `<T as Foo>::Assoc == _`
+  --> $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`)
+
 error[E0275]: overflow evaluating the requirement `<T as Foo>::Assoc: Bar`
   --> $DIR/recursive-self-normalization.rs:11:17
    |
@@ -35,7 +43,8 @@ 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 4 previous errors
+error: aborting due to 5 previous errors
 
 For more information about this error, try `rustc --explain E0275`.

tests/ui/traits/next-solver/temporary-ambiguity.rs

@@ -1,22 +0,0 @@
-// compile-flags: -Znext-solver
-// check-pass
-
-// Checks that we don't explode when we assemble >1 candidate for a goal.
-
-struct Wrapper<T>(T);
-
-trait Foo {}
-
-impl Foo for Wrapper<i32> {}
-
-impl Foo for Wrapper<()> {}
-
-fn needs_foo(_: impl Foo) {}
-
-fn main() {
-    let mut x = Default::default();
-    let w = Wrapper(x);
-    needs_foo(w);
-    x = 1;
-    let _ = x;
-}