1 files changed, 59 insertions, 0 deletions
diff --git a/tests/ui/repeat-expr/copy-check-deferred-before-fallback.rs b/tests/ui/repeat-expr/copy-check-deferred-before-fallback.rs
new file mode 100644
index 00000000000..4654d7483a6
--- /dev/null
+++ b/tests/ui/repeat-expr/copy-check-deferred-before-fallback.rs
@@ -0,0 +1,59 @@
+//@ check-pass
+
+#![feature(generic_arg_infer)]
+
+// Test that if we defer repeat expr copy checks to end of typechecking they're
+// checked before integer fallback occurs. We accomplish this by contriving a
+// situation where we have a goal that can be proven either via another repeat expr
+// check or by integer fallback. In the integer fallback case an array length would
+// be inferred to `2` requiring `NotCopy: Copy`, and in the repeat expr case it would
+// be inferred to `1`.
+
+use std::marker::PhantomData;
+
+struct NotCopy;
+
+struct Foo<T>(PhantomData<T>);
+
+impl Clone for Foo<u32> {
+    fn clone(&self) -> Self {
+        Foo(PhantomData)
+    }
+}
+
+impl Copy for Foo<u32> {}
+
+fn tie<T>(_: &T, _: [Foo<T>; 2]) {}
+
+trait Trait<const N: usize> {}
+
+impl Trait<2> for i32 {}
+impl Trait<1> for u32 {}
+
+fn make_goal<T: Trait<N>, const N: usize>(_: &T, _: [NotCopy; N]) {}
+
+fn main() {
+    let a = 1;
+    let b: [Foo<_>; 2] = [Foo(PhantomData); _];
+    tie(&a, b);
+    let c = [NotCopy; _];
+
+    // a is of type `?y`
+    // b is of type `[Foo<?y>; 2]`
+    // c is of type `[NotCopy; ?x]`
+    // there is a goal ?y: Trait<?x>` with two candidates:
+    // - `i32: Trait<2>`, ?y=i32 ?x=2 which requires `NotCopy: Copy` when expr checks happen
+    // - `u32: Trait<1>` ?y=u32 ?x=1 which doesnt require `NotCopy: Copy`
+    make_goal(&a, c);
+
+    // final repeat expr checks:
+    //
+    // `Foo<?y>; 2`
+    // - Foo<?y>: Copy
+    // - requires ?y=u32
+    //
+    // `NotCopy; ?x`
+    // - fails if fallback happens before repeat exprs as `i32: Trait<?x>` infers `?x=2`
+    // - succeeds if repeat expr checks happen first as `?y=u32` means `u32: Trait<?x>`
+    //    infers `?x=1`
+}