Add wf-projection-stress-65510 benchmark.

collector/benchmarks/README.md

@@ -90,3 +90,6 @@ programs.
   behavior](https://github.com/rust-lang/rust/pull/32062) in the past.
 - **unused-warnings**: Contains many unused imports, which caused [quadratic
   behavior](https://github.com/rust-lang/rust/issues/43572) in the past.
+- **wf-projection-stress-65510**: A stress test which showcases [quadratic
+  behavior](https://github.com/rust-lang/rust/issues/65510) (in the number of
+  associated type bounds).

collector/benchmarks/wf-projection-stress-65510/Cargo.toml

@@ -0,0 +1,3 @@
+[package]
+name = "wf-projection-stress-65510"
+version = "0.1.0"

collector/benchmarks/wf-projection-stress-65510/src/lib.rs

@@ -0,0 +1,36 @@
+macro_rules! stress {
+    (type $name:ident: $($i:expr,)*) => {
+        type $name: $(From<[(); $i]> + Into<[(); $i]> +)*;
+    };
+    (fn $($underscore:tt)*) => {
+        const _: () = {
+            $({fn _f<T: Trait>() {
+                #[derive(Copy, Clone)]
+                struct Foo<X>(X);
+                let $underscore = Foo(T::X::default()).clone();
+            }})*
+        };
+    };
+}
+
+trait Trait {
+    type X: Copy + Default;
+
+    // The bounds would normally be on many separate
+    // associated types, but that makes no difference.
+    stress!(type _Unused:
+        00, 01, 02, 03, 04, 05, 06, 07, 08, 09,
+        10, 11, 12, 13, 14, 15, 16, 17, 18, 19,
+
+        20, 21, 22, 23, 24, 25, 26, 27, 28, 29,
+        30, 31, 32, 33, 34, 35, 36, 37, 38, 39,
+
+        40, 41, 42, 43, 44, 45, 46, 47, 48, 49,
+        50, 51, 52, 53, 54, 55, 56, 57, 58, 59,
+
+        60, 61, 62, 63, 64, 65, 66, 67, 68, 69,
+        70, 71, 72, 73, 74, 75, 76, 77, 78, 79,
+    );
+}
+
+stress!(fn _ _ _ _ _ _ _ _ _ _);