From 4c710e72c42d988b09f7f3d877b1a280fdc46a49 Mon Sep 17 00:00:00 2001
From: Adam Perry <lol@anp.lol>
Date: Sun, 26 Jul 2020 09:53:24 -0700
Subject: [PATCH] Fix #[track_caller] shims for trait objects.

We were missing an Instance::resolve_for_fn_ptr in resolve_for_vtable.

Closes #74764.
---
 src/librustc_middle/ty/instance.rs            |  2 +-
 .../tracked-trait-obj.rs                      | 23 +++++++++++++++++++
 2 files changed, 24 insertions(+), 1 deletion(-)
 create mode 100644 src/test/ui/rfc-2091-track-caller/tracked-trait-obj.rs

diff --git a/src/librustc_middle/ty/instance.rs b/src/librustc_middle/ty/instance.rs
index f627d05d3e9d2..5c9c9ef6487f1 100644
--- a/src/librustc_middle/ty/instance.rs
+++ b/src/librustc_middle/ty/instance.rs
@@ -411,7 +411,7 @@ impl<'tcx> Instance<'tcx> {
             debug!(" => associated item with unsizeable self: Self");
             Some(Instance { def: InstanceDef::VtableShim(def_id), substs })
         } else {
-            Instance::resolve(tcx, param_env, def_id, substs).ok().flatten()
+            Instance::resolve_for_fn_ptr(tcx, param_env, def_id, substs)
         }
     }
 
diff --git a/src/test/ui/rfc-2091-track-caller/tracked-trait-obj.rs b/src/test/ui/rfc-2091-track-caller/tracked-trait-obj.rs
new file mode 100644
index 0000000000000..3b2a2238fa82d
--- /dev/null
+++ b/src/test/ui/rfc-2091-track-caller/tracked-trait-obj.rs
@@ -0,0 +1,23 @@
+// run-pass
+
+trait Tracked {
+    #[track_caller]
+    fn handle(&self) {
+        let location = std::panic::Location::caller();
+        assert_eq!(location.file(), file!());
+        // we only call this via trait object, so the def site should *always* be returned
+        assert_eq!(location.line(), line!() - 4);
+        assert_eq!(location.column(), 5);
+    }
+}
+
+impl Tracked for () {}
+impl Tracked for u8 {}
+
+fn main() {
+    let tracked: &dyn Tracked = &5u8;
+    tracked.handle();
+
+    const TRACKED: &dyn Tracked = &();
+    TRACKED.handle();
+}