Rollup merge of #104936 - cjgillot:self-rpit-orig-too, r=oli-obk

Ignore bivariant parameters in test_type_match.

#103491 made opaque types bivariant with respect of some of their lifetime parameters.  Because of this bivariance, some lifetime variables were not unified to anything during borrowck, and were considered as unequal by borrowck type test.

This PR makes type test ignore the bivariant parameters in test_type_match.

Fixes #104815

r? `@oli-obk`

Author: matthiaskrgr

compiler/rustc_infer/src/infer/outlives/test_type_match.rs

@@ -155,14 +155,17 @@ impl<'tcx> TypeRelation<'tcx> for Match<'tcx> {
         bug!()
     }
 
+    #[instrument(level = "trace", skip(self))]
     fn relate_with_variance<T: Relate<'tcx>>(
         &mut self,
-        _: ty::Variance,
+        variance: ty::Variance,
         _: ty::VarianceDiagInfo<'tcx>,
         a: T,
         b: T,
     ) -> RelateResult<'tcx, T> {
-        self.relate(a, b)
+        // Opaque types substs have lifetime parameters.
+        // We must not check them to be equal, as we never insert anything to make them so.
+        if variance != ty::Bivariant { self.relate(a, b) } else { Ok(a) }
     }
 
     #[instrument(skip(self), level = "debug")]

src/test/ui/impl-trait/issues/issue-104815.rs

@@ -0,0 +1,66 @@
+// check-pass
+
+struct It;
+
+struct Data {
+    items: Vec<It>,
+}
+
+impl Data {
+    fn new() -> Self {
+        Self {
+            items: vec![It, It],
+        }
+    }
+
+    fn content(&self) -> impl Iterator<Item = &It> {
+        self.items.iter()
+    }
+}
+
+struct Container<'a> {
+    name: String,
+    resolver: Box<dyn Resolver + 'a>,
+}
+
+impl<'a> Container<'a> {
+    fn new<R: Resolver + 'a>(name: &str, resolver: R) -> Self {
+        Self {
+            name: name.to_owned(),
+            resolver: Box::new(resolver),
+        }
+    }
+}
+
+trait Resolver {}
+
+impl<R: Resolver> Resolver for &R {}
+
+impl Resolver for It {}
+
+fn get<'a>(mut items: impl Iterator<Item = &'a It>) -> impl Resolver + 'a {
+    items.next().unwrap()
+}
+
+fn get2<'a, 'b: 'b>(mut items: impl Iterator<Item = &'a It>) -> impl Resolver + 'a {
+    items.next().unwrap()
+}
+
+fn main() {
+    let data = Data::new();
+    let resolver = get(data.content());
+
+    let _ = ["a", "b"]
+        .iter()
+        .map(|&n| Container::new(n, &resolver))
+        .map(|c| c.name)
+        .collect::<Vec<_>>();
+
+    let resolver = get2(data.content());
+
+    let _ = ["a", "b"]
+        .iter()
+        .map(|&n| Container::new(n, &resolver))
+        .map(|c| c.name)
+        .collect::<Vec<_>>();
+}