Auto merge of #55323 - nikomatsakis:nll-ICE-55219-and-55241, r=pnkfelix

introduce type-op for user-type ascription in NLL

Handle user-type ascription in a type operator, which gives us a lot more flexibility around the order in which we resolve things.

r? @pnkfelix

Fixes #55219
Fixes #55241

src/test/ui/nll/user-annotations/issue-55219.rs

@@ -0,0 +1,20 @@
+// Regression test for #55219:
+//
+// The `Self::HASH_LEN` here expands to a "self-type" where `T` is not
+// known. This unbound inference variable was causing an ICE.
+//
+// run-pass
+
+#![feature(nll)]
+
+pub struct Foo<T>(T);
+
+impl<T> Foo<T> {
+    const HASH_LEN: usize = 20;
+
+    fn stuff() {
+        let _ = Self::HASH_LEN;
+    }
+}
+
+fn main() { }

src/test/ui/nll/user-annotations/issue-55241.rs

@@ -0,0 +1,28 @@
+// Regression test for #55241:
+//
+// The reference to `C::HASHED_NULL_NODE` resulted in a type like `<C
+// as NodeCodec<_>>::Out`; normalizing this type requires knowing the
+// value of `_`; solving that requires having normalized, so we can
+// test against `C: NodeCodec<H>` in the environment.
+//
+// run-pass
+
+#![feature(nll)]
+
+pub trait Hasher {
+    type Out: Eq;
+}
+
+pub trait NodeCodec<H: Hasher> {
+    const HASHED_NULL_NODE: H::Out;
+}
+
+pub trait Trie<H: Hasher, C: NodeCodec<H>> {
+    /// Return the root of the trie.
+    fn root(&self) -> &H::Out;
+
+    /// Is the trie empty?
+    fn is_empty(&self) -> bool { *self.root() == C::HASHED_NULL_NODE }
+}
+
+fn main() { }

src/test/ui/regions/regions-free-region-ordering-caller1.nll.stderr

@@ -12,21 +12,6 @@ LL |     let z: &'a & usize = &(&y);
 LL | }
    | - temporary value is freed at the end of this statement
 
-error[E0597]: `y` does not live long enough
-  --> $DIR/regions-free-region-ordering-caller1.rs:19:27
-   |
-LL | fn call1<'a>(x: &'a usize) {
-   |          -- lifetime `'a` defined here
-...
-LL |     let z: &'a & usize = &(&y);
-   |            -----------    ^^^^ borrowed value does not live long enough
-   |            |
-   |            type annotation requires that `y` is borrowed for `'a`
-...
-LL | }
-   | - `y` dropped here while still borrowed
+error: aborting due to previous error
 
-error: aborting due to 2 previous errors
-
-Some errors occurred: E0597, E0716.
-For more information about an error, try `rustc --explain E0597`.
+For more information about this error, try `rustc --explain E0716`.