Add regression test for #69654

src/test/ui/const-generics/issues/issue-69654.rs

@@ -0,0 +1,18 @@
+#![feature(const_generics)]
+#![allow(incomplete_features)]
+
+trait Bar<O> {}
+impl<O> Bar<O> for [u8; O] {}
+//~^ ERROR expected value, found type parameter `O`
+
+struct Foo<const O: usize> {}
+impl<const O: usize> Foo<O>
+where
+    [u8; O]: Bar<[(); O]>,
+{
+    fn foo() {}
+}
+
+fn main() {
+    Foo::foo();
+}

src/test/ui/const-generics/issues/issue-69654.stderr

@@ -0,0 +1,14 @@
+error[E0423]: expected value, found type parameter `O`
+  --> $DIR/issue-69654.rs:5:25
+   |
+LL | impl<O> Bar<O> for [u8; O] {}
+   |                         ^ help: a tuple variant with a similar name exists: `Ok`
+   | 
+  ::: $SRC_DIR/libcore/result.rs:LL:COL
+   |
+LL |     Ok(#[stable(feature = "rust1", since = "1.0.0")] T),
+   |     --------------------------------------------------- similarly named tuple variant `Ok` defined here
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0423`.