Rollup merge of #109683 - compiler-errors:self-ty-overflow, r=lcnr

Check for overflow in `assemble_candidates_after_normalizing_self_ty`

Prevents a stack overflow (:warning: :exclamation:) in the new solver when we have param-env candidates that look like: `T: Trait<Assoc = <T as Trait>::Assoc>`

The current error message looks bad, but that's because we don't distinguish overflow and other ambiguity errors. I'll break that out into a separate PR since the fix may be controversial.

r? `@lcnr`

4 files changed, 52 insertions, 0 deletions

diff --git a/tests/ui/traits/new-solver/recursive-self-normalization-2.rs b/tests/ui/traits/new-solver/recursive-self-normalization-2.rs
new file mode 100644
index 00000000000..7417d6018a1
--- /dev/null
+++ b/tests/ui/traits/new-solver/recursive-self-normalization-2.rs
@@ -0,0 +1,19 @@
+// compile-flags: -Ztrait-solver=next
+
+trait Foo1 {
+    type Assoc1;
+}
+
+trait Foo2 {
+    type Assoc2;
+}
+
+trait Bar {}
+fn needs_bar<S: Bar>() {}
+
+fn test<T: Foo1<Assoc1 = <T as Foo2>::Assoc2> + Foo2<Assoc2 = <T as Foo1>::Assoc1>>() {
+    needs_bar::<T::Assoc1>();
+    //~^ ERROR type annotations needed
+}
+
+fn main() {}
diff --git a/tests/ui/traits/new-solver/recursive-self-normalization-2.stderr b/tests/ui/traits/new-solver/recursive-self-normalization-2.stderr
new file mode 100644
index 00000000000..29cfa47a105
--- /dev/null
+++ b/tests/ui/traits/new-solver/recursive-self-normalization-2.stderr
@@ -0,0 +1,9 @@
+error[E0282]: type annotations needed
+  --> $DIR/recursive-self-normalization-2.rs:15:5
+   |
+LL |     needs_bar::<T::Assoc1>();
+   |     ^^^^^^^^^^^^^^^^^^^^^^ cannot infer type of the type parameter `S` declared on the function `needs_bar`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0282`.
diff --git a/tests/ui/traits/new-solver/recursive-self-normalization.rs b/tests/ui/traits/new-solver/recursive-self-normalization.rs
new file mode 100644
index 00000000000..f3e3d71d813
--- /dev/null
+++ b/tests/ui/traits/new-solver/recursive-self-normalization.rs
@@ -0,0 +1,15 @@
+// compile-flags: -Ztrait-solver=next
+
+trait Foo {
+    type Assoc;
+}
+
+trait Bar {}
+fn needs_bar<S: Bar>() {}
+
+fn test<T: Foo<Assoc = <T as Foo>::Assoc>>() {
+    needs_bar::<T::Assoc>();
+    //~^ ERROR type annotations needed
+}
+
+fn main() {}
diff --git a/tests/ui/traits/new-solver/recursive-self-normalization.stderr b/tests/ui/traits/new-solver/recursive-self-normalization.stderr
new file mode 100644
index 00000000000..ba39981893d
--- /dev/null
+++ b/tests/ui/traits/new-solver/recursive-self-normalization.stderr
@@ -0,0 +1,9 @@
+error[E0282]: type annotations needed
+  --> $DIR/recursive-self-normalization.rs:11:5
+   |
+LL |     needs_bar::<T::Assoc>();
+   |     ^^^^^^^^^^^^^^^^^^^^^ cannot infer type of the type parameter `S` declared on the function `needs_bar`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0282`.