Rollup merge of #86764 - estebank:issue-86756, r=pnkfelix

Avoid ICE on type error recovery

Fix #86756

src/test/ui/issues/issue-86756.rs

@@ -0,0 +1,12 @@
+trait Foo<T, T = T> {}
+//~^ ERROR the name `T` is already used for a generic parameter in this item's generic parameters
+
+fn eq<A, B>() {
+    eq::<dyn, Foo>
+    //~^ ERROR cannot find type `dyn` in this scope
+    //~| ERROR missing generics for trait `Foo`
+    //~| WARN trait objects without an explicit `dyn` are deprecated
+    //~| WARN this is accepted in the current edition
+}
+
+fn main() {}

src/test/ui/issues/issue-86756.stderr

@@ -0,0 +1,46 @@
+error[E0403]: the name `T` is already used for a generic parameter in this item's generic parameters
+  --> $DIR/issue-86756.rs:1:14
+   |
+LL | trait Foo<T, T = T> {}
+   |           -  ^ already used
+   |           |
+   |           first use of `T`
+
+error[E0412]: cannot find type `dyn` in this scope
+  --> $DIR/issue-86756.rs:5:10
+   |
+LL | fn eq<A, B>() {
+   |           - help: you might be missing a type parameter: `, dyn`
+LL |     eq::<dyn, Foo>
+   |          ^^^ not found in this scope
+
+warning: trait objects without an explicit `dyn` are deprecated
+  --> $DIR/issue-86756.rs:5:15
+   |
+LL |     eq::<dyn, Foo>
+   |               ^^^ help: use `dyn`: `dyn Foo`
+   |
+   = note: `#[warn(bare_trait_objects)]` on by default
+   = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
+   = note: for more information, see issue #80165 <https://github.com/rust-lang/rust/issues/80165>
+
+error[E0107]: missing generics for trait `Foo`
+  --> $DIR/issue-86756.rs:5:15
+   |
+LL |     eq::<dyn, Foo>
+   |               ^^^ expected at least 1 generic argument
+   |
+note: trait defined here, with at least 1 generic parameter: `T`
+  --> $DIR/issue-86756.rs:1:7
+   |
+LL | trait Foo<T, T = T> {}
+   |       ^^^ -
+help: add missing generic argument
+   |
+LL |     eq::<dyn, Foo<T>>
+   |               ^^^^^^
+
+error: aborting due to 3 previous errors; 1 warning emitted
+
+Some errors have detailed explanations: E0107, E0403, E0412.
+For more information about an error, try `rustc --explain E0107`.