1 files changed, 95 insertions, 0 deletions
diff --git a/tests/ui/polymorphization/predicates.rs b/tests/ui/polymorphization/predicates.rs
new file mode 100644
index 00000000000..6a5fc2e33de
--- /dev/null
+++ b/tests/ui/polymorphization/predicates.rs
@@ -0,0 +1,95 @@
+// build-fail
+// compile-flags: -Copt-level=0 -Zpolymorphize=on
+
+#![feature(rustc_attrs)]
+
+// This test checks that `T` is considered used in `foo`, because it is used in a predicate for
+// `I`, which is used.
+
+#[rustc_polymorphize_error]
+fn bar<I>() {
+    //~^ ERROR item has unused generic parameters
+}
+
+#[rustc_polymorphize_error]
+fn foo<I, T>(_: I)
+//~^ ERROR item has unused generic parameters
+where
+    I: Iterator<Item = T>,
+{
+    bar::<I>()
+}
+
+#[rustc_polymorphize_error]
+fn baz<I, T>(_: I)
+//~^ ERROR item has unused generic parameters
+where
+    std::iter::Repeat<I>: Iterator<Item = T>,
+{
+    bar::<I>()
+}
+
+// In addition, check that `I` is considered used in `next::{{closure}}`, because `T` is used and
+// `T` is really just `I::Item`. `E` is used due to the fixed-point marking of predicates.
+
+pub(crate) struct Foo<'a, I, E>(I, &'a E);
+
+impl<'a, I, T: 'a, E> Iterator for Foo<'a, I, E>
+where
+    I: Iterator<Item = &'a (T, E)>,
+{
+    type Item = T;
+
+    #[rustc_polymorphize_error]
+    fn next(&mut self) -> Option<Self::Item> {
+        self.find(|_| true)
+        //~^ ERROR item has unused generic parameters
+    }
+}
+
+// Furthermore, check that `B` is considered used because `C` is used, and that `A` is considered
+// used because `B` is now used.
+
+trait Baz<Z> {}
+
+impl Baz<u16> for u8 {}
+impl Baz<u32> for u16 {}
+
+#[rustc_polymorphize_error]
+fn quux<A, B, C: Default>() -> usize
+//~^ ERROR item has unused generic parameters
+where
+    A: Baz<B>,
+    B: Baz<C>,
+{
+    std::mem::size_of::<C>()
+}
+
+// Finally, check that `F` is considered used because `G` is used when neither are in the self-ty
+// of the predicate.
+
+trait Foobar<F, G> {}
+
+impl Foobar<u32, u32> for () {}
+
+#[rustc_polymorphize_error]
+fn foobar<F, G>() -> usize
+//~^ ERROR item has unused generic parameters
+where
+    (): Foobar<F, G>,
+{
+    std::mem::size_of::<G>()
+}
+
+fn main() {
+    let x = &[2u32];
+    foo(x.iter());
+    baz(x.iter());
+
+    let mut a = Foo([(1u32, 1u16)].iter(), &1u16);
+    let _ = a.next();
+
+    let _ = quux::<u8, u16, u32>();
+
+    let _ = foobar::<u32, u32>();
+}