Rollup merge of #102016 - lcnr:given-OutlivesEnvironment, r=jackh726

implied_bounds: deal with inference vars

fixes #101951

while computing implied bounds for `<<T as ConstructionFirm>::Builder as BuilderFn<'_>>::Output` normalization replaces a projection with an inference var (adding a `Projection` obligation). Until we prove that obligation, this inference var remains unknown, which caused us to miss an implied bound necessary to prove that the unnormalized projection from the trait method signature is wf.

r? types

1 files changed, 50 insertions, 0 deletions

diff --git a/src/test/ui/implied-bounds/issue-101951.rs b/src/test/ui/implied-bounds/issue-101951.rs
new file mode 100644
index 00000000000..108fef8a15f
--- /dev/null
+++ b/src/test/ui/implied-bounds/issue-101951.rs
@@ -0,0 +1,50 @@
+// Taken directly from that issue.
+//
+// This test detected that we didn't correctly resolve
+// inference variables when computing implied bounds.
+//
+// check-pass
+pub trait BuilderFn<'a> {
+    type Output;
+}
+
+impl<'a, F, Out> BuilderFn<'a> for F
+where
+    F: FnOnce(&'a mut ()) -> Out,
+{
+    type Output = Out;
+}
+
+pub trait ConstructionFirm {
+    type Builder: for<'a> BuilderFn<'a>;
+}
+
+pub trait Campus<T>
+where
+    T: ConstructionFirm,
+{
+    fn add_building(
+        &mut self,
+        building: &mut <<T as ConstructionFirm>::Builder as BuilderFn<'_>>::Output,
+    );
+}
+
+struct ArchitectsInc {}
+
+impl ConstructionFirm for ArchitectsInc {
+    type Builder = fn(&mut ()) -> PrettyCondo<'_>;
+}
+
+struct PrettyCondo<'a> {
+    _marker: &'a mut (),
+}
+
+struct CondoEstate {}
+
+impl Campus<ArchitectsInc> for CondoEstate {
+    fn add_building(&mut self, _building: &mut PrettyCondo<'_>) {
+        todo!()
+    }
+}
+
+fn main() {}