From ed34354bfa4f98da2883fdbba4453c571dde1ef7 Mon Sep 17 00:00:00 2001
From: Deadbeef <ent3rm4n@gmail.com>
Date: Sat, 25 Feb 2023 08:39:05 +0000
Subject: [PATCH] Do not lint unresolved trait for ineffective unstable trait
 impl

---
 compiler/rustc_passes/src/stability.rs                   | 5 ++++-
 .../ui/stability-attribute/unresolved_stability_lint.rs  | 8 ++++++++
 .../stability-attribute/unresolved_stability_lint.stderr | 9 +++++++++
 3 files changed, 21 insertions(+), 1 deletion(-)
 create mode 100644 tests/ui/stability-attribute/unresolved_stability_lint.rs
 create mode 100644 tests/ui/stability-attribute/unresolved_stability_lint.stderr

diff --git a/compiler/rustc_passes/src/stability.rs b/compiler/rustc_passes/src/stability.rs
index 2e736039fb5..d7bf96b5237 100644
--- a/compiler/rustc_passes/src/stability.rs
+++ b/compiler/rustc_passes/src/stability.rs
@@ -748,7 +748,10 @@ impl<'tcx> Visitor<'tcx> for Checker<'tcx> {
                         let mut c = CheckTraitImplStable { tcx: self.tcx, fully_stable: true };
                         c.visit_ty(self_ty);
                         c.visit_trait_ref(t);
-                        if c.fully_stable {
+
+                        // do not lint when the trait isn't resolved, since resolution error should
+                        // be fixed first
+                        if t.path.res != Res::Err && c.fully_stable {
                             self.tcx.struct_span_lint_hir(
                                 INEFFECTIVE_UNSTABLE_TRAIT_IMPL,
                                 item.hir_id(),
diff --git a/tests/ui/stability-attribute/unresolved_stability_lint.rs b/tests/ui/stability-attribute/unresolved_stability_lint.rs
new file mode 100644
index 00000000000..818d228bc91
--- /dev/null
+++ b/tests/ui/stability-attribute/unresolved_stability_lint.rs
@@ -0,0 +1,8 @@
+#![feature(staged_api)]
+#![stable(feature = "uwu", since = "1.0.0")]
+
+#[unstable(feature = "foo", issue = "none")]
+impl Foo for () {}
+//~^ ERROR cannot find trait `Foo` in this scope
+
+fn main() {}
diff --git a/tests/ui/stability-attribute/unresolved_stability_lint.stderr b/tests/ui/stability-attribute/unresolved_stability_lint.stderr
new file mode 100644
index 00000000000..11d6abcaf36
--- /dev/null
+++ b/tests/ui/stability-attribute/unresolved_stability_lint.stderr
@@ -0,0 +1,9 @@
+error[E0405]: cannot find trait `Foo` in this scope
+  --> $DIR/unresolved_stability_lint.rs:5:6
+   |
+LL | impl Foo for () {}
+   |      ^^^ not found in this scope
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0405`.