Auto merge of #105350 - compiler-errors:faster-binder-relate, r=oli-obk

Fast-path some binder relations

A simpler approach than #104598

Fixes #104583

r? types

2 files changed, 38 insertions, 0 deletions

diff --git a/src/test/ui/higher-rank-trait-bounds/hang-on-deeply-nested-dyn.rs b/src/test/ui/higher-rank-trait-bounds/hang-on-deeply-nested-dyn.rs
new file mode 100644
index 00000000000..d34b7a29623
--- /dev/null
+++ b/src/test/ui/higher-rank-trait-bounds/hang-on-deeply-nested-dyn.rs
@@ -0,0 +1,16 @@
+// normalize-stderr-test: "long-type-\d+" -> "long-type-hash"
+
+fn id(
+    f: &dyn Fn(u32),
+) -> &dyn Fn(
+    &dyn Fn(
+        &dyn Fn(
+            &dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(u32))))))))),
+        ),
+    ),
+) {
+    f
+    //~^ ERROR mismatched types
+}
+
+fn main() {}
diff --git a/src/test/ui/higher-rank-trait-bounds/hang-on-deeply-nested-dyn.stderr b/src/test/ui/higher-rank-trait-bounds/hang-on-deeply-nested-dyn.stderr
new file mode 100644
index 00000000000..71e196c3227
--- /dev/null
+++ b/src/test/ui/higher-rank-trait-bounds/hang-on-deeply-nested-dyn.stderr
@@ -0,0 +1,22 @@
+error[E0308]: mismatched types
+  --> $DIR/hang-on-deeply-nested-dyn.rs:12:5
+   |
+LL |   ) -> &dyn Fn(
+   |  ______-
+LL | |     &dyn Fn(
+LL | |         &dyn Fn(
+LL | |             &dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(&dyn Fn(u32))))))))),
+LL | |         ),
+LL | |     ),
+LL | | ) {
+   | |_- expected `&dyn for<'a> Fn(&'a (dyn for<'a> Fn(&'a (dyn for<'a> Fn(&'a (dyn for<'a> Fn(&'a (dyn for<'a> Fn(&'a (dyn for<'a> Fn(&'a (dyn for<'a> Fn(&'a (dyn for<'a> Fn(&'a (dyn for<'a> Fn(&'a (dyn for<'a> Fn(&'a (dyn for<'a> Fn(&'a (dyn Fn(u32) + 'a)) + 'a)) + 'a)) + 'a)) + 'a)) + 'a)) + 'a)) + 'a)) + 'a)) + 'a)) + 'a))` because of return type
+LL |       f
+   |       ^ expected reference, found `u32`
+   |
+   = note: expected reference `&dyn for<'a> Fn(&'a (dyn for<'a> Fn(&'a (dyn for<'a> Fn(&'a (dyn for<'a> Fn(&'a ...) + 'a)) + 'a)) + 'a))`
+           the full type name has been written to '$TEST_BUILD_DIR/higher-rank-trait-bounds/hang-on-deeply-nested-dyn/hang-on-deeply-nested-dyn.long-type-hash.txt'
+              found reference `&dyn Fn(u32)`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0308`.