From b5782bad743f596061e9c75d0a3f8a8ed8213b03 Mon Sep 17 00:00:00 2001
From: Yuki Okushi <jtitor@2k36.org>
Date: Thu, 1 Apr 2021 10:45:42 +0900
Subject: [PATCH] Catch a bad placeholder type error for statics in `extern`s

---
 compiler/rustc_typeck/src/collect.rs                   | 10 ++++++++--
 .../typeck/issue-83621-placeholder-static-in-extern.rs |  7 +++++++
 .../issue-83621-placeholder-static-in-extern.stderr    |  9 +++++++++
 3 files changed, 24 insertions(+), 2 deletions(-)
 create mode 100644 src/test/ui/typeck/issue-83621-placeholder-static-in-extern.rs
 create mode 100644 src/test/ui/typeck/issue-83621-placeholder-static-in-extern.stderr

diff --git a/compiler/rustc_typeck/src/collect.rs b/compiler/rustc_typeck/src/collect.rs
index 0ef5f4d1c180c..479098a5a7acb 100644
--- a/compiler/rustc_typeck/src/collect.rs
+++ b/compiler/rustc_typeck/src/collect.rs
@@ -735,8 +735,14 @@ fn convert_item(tcx: TyCtxt<'_>, item_id: hir::ItemId) {
                 tcx.ensure().generics_of(item.def_id);
                 tcx.ensure().type_of(item.def_id);
                 tcx.ensure().predicates_of(item.def_id);
-                if let hir::ForeignItemKind::Fn(..) = item.kind {
-                    tcx.ensure().fn_sig(item.def_id);
+                match item.kind {
+                    hir::ForeignItemKind::Fn(..) => tcx.ensure().fn_sig(item.def_id),
+                    hir::ForeignItemKind::Static(..) => {
+                        let mut visitor = PlaceholderHirTyCollector::default();
+                        visitor.visit_foreign_item(item);
+                        placeholder_type_error(tcx, None, &[], visitor.0, false, None);
+                    }
+                    _ => (),
                 }
             }
         }
diff --git a/src/test/ui/typeck/issue-83621-placeholder-static-in-extern.rs b/src/test/ui/typeck/issue-83621-placeholder-static-in-extern.rs
new file mode 100644
index 0000000000000..16ec2a546434c
--- /dev/null
+++ b/src/test/ui/typeck/issue-83621-placeholder-static-in-extern.rs
@@ -0,0 +1,7 @@
+// Regression test for #83621.
+
+extern "C" {
+    static x: _; //~ ERROR: [E0121]
+}
+
+fn main() {}
diff --git a/src/test/ui/typeck/issue-83621-placeholder-static-in-extern.stderr b/src/test/ui/typeck/issue-83621-placeholder-static-in-extern.stderr
new file mode 100644
index 0000000000000..b1bec4c0827f9
--- /dev/null
+++ b/src/test/ui/typeck/issue-83621-placeholder-static-in-extern.stderr
@@ -0,0 +1,9 @@
+error[E0121]: the type placeholder `_` is not allowed within types on item signatures
+  --> $DIR/issue-83621-placeholder-static-in-extern.rs:4:15
+   |
+LL |     static x: _;
+   |               ^ not allowed in type signatures
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0121`.