From e5c159cf9026af6304ef07fd151fe7c500ed2510 Mon Sep 17 00:00:00 2001
From: Michael Goulet <michael@errs.io>
Date: Tue, 27 Dec 2022 17:10:21 +0000
Subject: [PATCH] Provide local extern function arg names

---
 compiler/rustc_middle/src/hir/mod.rs          |  6 ++++-
 .../extern-fn-arg-names.rs                    |  9 +++++++
 .../extern-fn-arg-names.stderr                | 26 +++++++++++++++++++
 3 files changed, 40 insertions(+), 1 deletion(-)
 create mode 100644 src/test/ui/argument-suggestions/extern-fn-arg-names.rs
 create mode 100644 src/test/ui/argument-suggestions/extern-fn-arg-names.stderr

diff --git a/compiler/rustc_middle/src/hir/mod.rs b/compiler/rustc_middle/src/hir/mod.rs
index 3f6e29ad611c9..a633201e3d9ae 100644
--- a/compiler/rustc_middle/src/hir/mod.rs
+++ b/compiler/rustc_middle/src/hir/mod.rs
@@ -160,9 +160,13 @@ pub fn provide(providers: &mut Providers) {
         } else if let Node::TraitItem(&TraitItem {
             kind: TraitItemKind::Fn(_, TraitFn::Required(idents)),
             ..
+        })
+        | Node::ForeignItem(&ForeignItem {
+            kind: ForeignItemKind::Fn(_, idents, _),
+            ..
         }) = hir.get(hir_id)
         {
-            tcx.arena.alloc_slice(idents)
+            idents
         } else {
             span_bug!(hir.span(hir_id), "fn_arg_names: unexpected item {:?}", id);
         }
diff --git a/src/test/ui/argument-suggestions/extern-fn-arg-names.rs b/src/test/ui/argument-suggestions/extern-fn-arg-names.rs
new file mode 100644
index 0000000000000..6c925a3d653c7
--- /dev/null
+++ b/src/test/ui/argument-suggestions/extern-fn-arg-names.rs
@@ -0,0 +1,9 @@
+extern "Rust" {
+    fn dstfn(src: i32, dst: err);
+    //~^ ERROR cannot find type `err` in this scope
+}
+
+fn main() {
+    dstfn(1);
+    //~^ ERROR this function takes 2 arguments but 1 argument was supplied
+}
diff --git a/src/test/ui/argument-suggestions/extern-fn-arg-names.stderr b/src/test/ui/argument-suggestions/extern-fn-arg-names.stderr
new file mode 100644
index 0000000000000..f6bc84c1203ad
--- /dev/null
+++ b/src/test/ui/argument-suggestions/extern-fn-arg-names.stderr
@@ -0,0 +1,26 @@
+error[E0412]: cannot find type `err` in this scope
+  --> $DIR/extern-fn-arg-names.rs:2:29
+   |
+LL |     fn dstfn(src: i32, dst: err);
+   |                             ^^^ not found in this scope
+
+error[E0061]: this function takes 2 arguments but 1 argument was supplied
+  --> $DIR/extern-fn-arg-names.rs:7:5
+   |
+LL |     dstfn(1);
+   |     ^^^^^--- an argument is missing
+   |
+note: function defined here
+  --> $DIR/extern-fn-arg-names.rs:2:8
+   |
+LL |     fn dstfn(src: i32, dst: err);
+   |        ^^^^^
+help: provide the argument
+   |
+LL |     dstfn(1, /* dst */);
+   |          ~~~~~~~~~~~~~~
+
+error: aborting due to 2 previous errors
+
+Some errors have detailed explanations: E0061, E0412.
+For more information about an error, try `rustc --explain E0061`.