From 3c7c694e734b6bcc41663eaf230a7f26c19de0f4 Mon Sep 17 00:00:00 2001
From: Manish Goregaokar <manishsmail@gmail.com>
Date: Mon, 2 Jan 2023 14:25:24 -0800
Subject: [PATCH] Document rustc_ast::Extern variants

---
 compiler/rustc_ast/src/ast.rs | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/compiler/rustc_ast/src/ast.rs b/compiler/rustc_ast/src/ast.rs
index 4ad9981991d3..9f38deacca41 100644
--- a/compiler/rustc_ast/src/ast.rs
+++ b/compiler/rustc_ast/src/ast.rs
@@ -2705,8 +2705,19 @@ impl Item {
 /// `extern` qualifier on a function item or function type.
 #[derive(Clone, Copy, Encodable, Decodable, Debug)]
 pub enum Extern {
+    /// No explicit extern keyword was used
+    ///
+    /// E.g. `fn foo() {}`
     None,
+    /// An explicit extern keyword was used, but with implicit ABI
+    ///
+    /// E.g. `extern fn foo() {}`
+    ///
+    /// This is just `extern "C"` (see `rustc_target::spec::abi::Abi::FALLBACK`)
     Implicit(Span),
+    /// An explicit extern keyword was used with an explicit ABI
+    ///
+    /// E.g. `extern "C" fn foo() {}`
     Explicit(StrLit, Span),
 }