Add regression tests for pretty-printing inherent projections

tests/ui/associated-inherent-types/issue-111879-0.rs

@@ -0,0 +1,14 @@
+#![feature(inherent_associated_types)]
+#![allow(incomplete_features)]
+
+// Check that we don't crash when printing inherent projections in diagnostics.
+
+pub struct Carrier<'a>(&'a ());
+
+pub type User = for<'b> fn(Carrier<'b>::Focus<i32>);
+
+impl<'a> Carrier<'a> {
+    pub type Focus<T> = &'a mut User; //~ ERROR overflow evaluating associated type
+}
+
+fn main() {}

tests/ui/associated-inherent-types/issue-111879-0.stderr

@@ -0,0 +1,8 @@
+error: overflow evaluating associated type `Carrier<'b>::Focus<i32>`
+  --> $DIR/issue-111879-0.rs:11:25
+   |
+LL |     pub type Focus<T> = &'a mut User;
+   |                         ^^^^^^^^^^^^
+
+error: aborting due to previous error
+

tests/ui/associated-inherent-types/issue-111879-1.rs

@@ -0,0 +1,12 @@
+#![feature(inherent_associated_types)]
+#![allow(incomplete_features)]
+
+// Check that we don't crash when printing inherent projections in diagnostics.
+
+struct Foo<T>(T);
+
+impl<'a> Foo<fn(&'a ())> {
+    type Assoc = &'a ();
+}
+
+fn main(_: for<'a> fn(Foo<fn(&'a ())>::Assoc)) {} //~ ERROR `main` function has wrong type

tests/ui/associated-inherent-types/issue-111879-1.stderr

@@ -0,0 +1,12 @@
+error[E0580]: `main` function has wrong type
+  --> $DIR/issue-111879-1.rs:12:1
+   |
+LL | fn main(_: for<'a> fn(Foo<fn(&'a ())>::Assoc)) {}
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ incorrect number of function parameters
+   |
+   = note: expected fn pointer `fn()`
+              found fn pointer `fn(for<'a> fn(Foo<fn(&'a ())>::Assoc))`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0580`.