add test for #104779 opaque types, patterns and subtyping ICE: IndexMap: key not found

Fixes #104779

Author: matthiaskrgr

tests/ui/borrowck/opaque-types-patterns-subtyping-ice-104779.rs

@@ -0,0 +1,26 @@
+// issue: rust-lang/rust#104779
+// ICE region infer, IndexMap: key not found
+
+struct Inv<'a>(&'a mut &'a ());
+enum Foo<T> {
+    Bar,
+    Var(T),
+}
+type Subtype = Foo<for<'a, 'b> fn(Inv<'a>, Inv<'b>)>;
+type Supertype = Foo<for<'a> fn(Inv<'a>, Inv<'a>)>;
+
+fn foo() -> impl Sized {
+//~^ WARN function cannot return without recursing
+    loop {
+        match foo() {
+        //~^ ERROR higher-ranked subtype error
+        //~^^ ERROR higher-ranked subtype error
+            Subtype::Bar => (),
+            //~^ ERROR higher-ranked subtype error
+            //~^^ ERROR higher-ranked subtype error
+            Supertype::Var(x) => {}
+        }
+    }
+}
+
+pub fn main() {}

tests/ui/borrowck/opaque-types-patterns-subtyping-ice-104779.stderr

@@ -0,0 +1,42 @@
+warning: function cannot return without recursing
+  --> $DIR/opaque-types-patterns-subtyping-ice-104779.rs:12:1
+   |
+LL | fn foo() -> impl Sized {
+   | ^^^^^^^^^^^^^^^^^^^^^^ cannot return without recursing
+...
+LL |         match foo() {
+   |               ----- recursive call site
+   |
+   = help: a `loop` may express intention better if this is on purpose
+   = note: `#[warn(unconditional_recursion)]` on by default
+
+error: higher-ranked subtype error
+  --> $DIR/opaque-types-patterns-subtyping-ice-104779.rs:15:15
+   |
+LL |         match foo() {
+   |               ^^^^^
+
+error: higher-ranked subtype error
+  --> $DIR/opaque-types-patterns-subtyping-ice-104779.rs:15:15
+   |
+LL |         match foo() {
+   |               ^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: higher-ranked subtype error
+  --> $DIR/opaque-types-patterns-subtyping-ice-104779.rs:18:13
+   |
+LL |             Subtype::Bar => (),
+   |             ^^^^^^^^^^^^
+
+error: higher-ranked subtype error
+  --> $DIR/opaque-types-patterns-subtyping-ice-104779.rs:18:13
+   |
+LL |             Subtype::Bar => (),
+   |             ^^^^^^^^^^^^
+   |
+   = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
+
+error: aborting due to 4 previous errors; 1 warning emitted
+