From ecf2a9b75ec591db6e89f4bde391b87f35c2ea08 Mon Sep 17 00:00:00 2001
From: Ezra Shaw <ezrasure@outlook.com>
Date: Thu, 13 Apr 2023 20:29:41 +1200
Subject: [PATCH] fix: skip implied bounds if unconstrained lifetime exists

---
 .../src/traits/outlives_bounds.rs             | 11 ++++++++-
 tests/ui/implied-bounds/issue-110161.rs       | 24 +++++++++++++++++++
 tests/ui/implied-bounds/issue-110161.stderr   | 12 ++++++++++
 3 files changed, 46 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/implied-bounds/issue-110161.rs
 create mode 100644 tests/ui/implied-bounds/issue-110161.stderr

diff --git a/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs b/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
index cff3d277a78..64be4a55708 100644
--- a/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
+++ b/compiler/rustc_trait_selection/src/traits/outlives_bounds.rs
@@ -55,7 +55,16 @@ impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
     ) -> Vec<OutlivesBound<'tcx>> {
         let ty = self.resolve_vars_if_possible(ty);
         let ty = OpportunisticRegionResolver::new(self).fold_ty(ty);
-        assert!(!ty.needs_infer());
+
+        // We must avoid processing constrained lifetime variables in implied
+        // bounds. See #110161 for context.
+        if ty.needs_infer() {
+            self.tcx.sess.delay_span_bug(
+                self.tcx.source_span_untracked(body_id),
+                "skipped implied_outlives_bounds due to unconstrained lifetimes",
+            );
+            return vec![];
+        }
 
         let span = self.tcx.def_span(body_id);
         let result = param_env
diff --git a/tests/ui/implied-bounds/issue-110161.rs b/tests/ui/implied-bounds/issue-110161.rs
new file mode 100644
index 00000000000..ca75026ffe8
--- /dev/null
+++ b/tests/ui/implied-bounds/issue-110161.rs
@@ -0,0 +1,24 @@
+// ICE regression relating to unconstrained lifetimes in implied
+// bounds. See #110161.
+
+// compile-flags: --crate-type=lib
+
+trait Trait {
+    type Ty;
+}
+
+// erroneous `Ty` impl
+impl Trait for () {
+//~^ ERROR not all trait items implemented, missing: `Ty` [E0046]
+}
+
+// `'lt` is not constrained by the erroneous `Ty`
+impl<'lt, T> Trait for Box<T>
+where
+    T: Trait<Ty = &'lt ()>,
+{
+    type Ty = &'lt ();
+}
+
+// unconstrained lifetime appears in implied bounds
+fn test(_: <Box<()> as Trait>::Ty) {}
diff --git a/tests/ui/implied-bounds/issue-110161.stderr b/tests/ui/implied-bounds/issue-110161.stderr
new file mode 100644
index 00000000000..c76b4737626
--- /dev/null
+++ b/tests/ui/implied-bounds/issue-110161.stderr
@@ -0,0 +1,12 @@
+error[E0046]: not all trait items implemented, missing: `Ty`
+  --> $DIR/issue-110161.rs:11:1
+   |
+LL |     type Ty;
+   |     ------- `Ty` from trait
+...
+LL | impl Trait for () {
+   | ^^^^^^^^^^^^^^^^^ missing `Ty` in implementation
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0046`.