polymorphize: `I` used if `T` used in `I: Foo<T>`

This commit adjusts polymorphization's handling of predicates so that
after ensuring that `T` is used in `I: Foo<T>` if `I` is used, it now
ensures that `I` is used if `T` is used in `I: Foo<T>`. This is
necessary to mark generic parameters that only exist in impl parameters
as used - thereby avoiding symbol clashes when using the new mangling
scheme.

Signed-off-by: David Wood <david@davidtw.co>

2 files changed, 70 insertions, 0 deletions

diff --git a/src/test/ui/polymorphization/predicates.rs b/src/test/ui/polymorphization/predicates.rs
index 82a94933b47..60555dc12dc 100644
--- a/src/test/ui/polymorphization/predicates.rs
+++ b/src/test/ui/polymorphization/predicates.rs
@@ -18,7 +18,55 @@ where
     bar::<I>()
 }
 
+#[rustc_polymorphize_error]
+fn baz<I, T>(_: I)
+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)
+    }
+}
+
+// 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
+where
+    A: Baz<B>,
+    B: Baz<C>,
+{
+    std::mem::size_of::<C>()
+}
+
 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>();
 }
diff --git a/src/test/ui/polymorphization/symbol-ambiguity.rs b/src/test/ui/polymorphization/symbol-ambiguity.rs
new file mode 100644
index 00000000000..d97bae183d9
--- /dev/null
+++ b/src/test/ui/polymorphization/symbol-ambiguity.rs
@@ -0,0 +1,22 @@
+// build-pass
+// compile-flags: -Zpolymorphize=on -Zsymbol-mangling-version=v0
+
+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;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.find(|_| true)
+    }
+}
+
+fn main() {
+    let mut a = Foo([(1u32, 1u16)].iter(), &1u16);
+    let mut b = Foo([(1u16, 1u32)].iter(), &1u32);
+    let _ = a.next();
+    let _ = b.next();
+}