lint missing docs for extern items

compiler/rustc_lint/src/builtin.rs

@@ -613,6 +613,19 @@ impl<'tcx> LateLintPass<'tcx> for MissingDoc {
         );
     }
 
+    fn check_foreign_item(&mut self, cx: &LateContext<'_>, foreign_item: &hir::ForeignItem<'_>) {
+        let def_id = cx.tcx.hir().local_def_id(foreign_item.hir_id);
+        let (article, desc) = cx.tcx.article_and_description(def_id.to_def_id());
+        self.check_missing_docs_attrs(
+            cx,
+            Some(foreign_item.hir_id),
+            &foreign_item.attrs,
+            foreign_item.span,
+            article,
+            desc,
+        );
+    }
+
     fn check_struct_field(&mut self, cx: &LateContext<'_>, sf: &hir::StructField<'_>) {
         if !sf.is_positional() {
             self.check_missing_docs_attrs(

src/test/ui/lint/lint-missing-doc.rs

@@ -2,7 +2,7 @@
 // injected intrinsics by the compiler.
 #![deny(missing_docs)]
 #![allow(dead_code)]
-#![feature(associated_type_defaults)]
+#![feature(associated_type_defaults, extern_types)]
 
 //! Some garbage docs for the crate here
 #![doc="More garbage"]
@@ -183,4 +183,21 @@ pub mod public_interface {
     pub use internal_impl::globbed::*;
 }
 
+extern "C" {
+    /// dox
+    pub fn extern_fn_documented(f: f32) -> f32;
+    pub fn extern_fn_undocumented(f: f32) -> f32;
+    //~^ ERROR: missing documentation for a function
+
+    /// dox
+    pub static EXTERN_STATIC_DOCUMENTED: u8;
+    pub static EXTERN_STATIC_UNDOCUMENTED: u8;
+    //~^ ERROR: missing documentation for a static
+
+    /// dox
+    pub type ExternTyDocumented;
+    pub type ExternTyUndocumented;
+    //~^ ERROR: missing documentation for a foreign type
+}
+
 fn main() {}

src/test/ui/lint/lint-missing-doc.stderr

@@ -118,5 +118,23 @@ error: missing documentation for a function
 LL |         pub fn also_undocumented1() {}
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 19 previous errors
+error: missing documentation for a function
+  --> $DIR/lint-missing-doc.rs:189:5
+   |
+LL |     pub fn extern_fn_undocumented(f: f32) -> f32;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: missing documentation for a static
+  --> $DIR/lint-missing-doc.rs:194:5
+   |
+LL |     pub static EXTERN_STATIC_UNDOCUMENTED: u8;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: missing documentation for a foreign type
+  --> $DIR/lint-missing-doc.rs:199:5
+   |
+LL |     pub type ExternTyUndocumented;
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 22 previous errors