From e054985771ec8e3c964b061bd12a5a33fcf25658 Mon Sep 17 00:00:00 2001
From: David Tolnay <dtolnay@gmail.com>
Date: Sun, 14 May 2023 10:46:55 +0200
Subject: [PATCH] Parse builtin# syntax

---
 src/expr.rs | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/src/expr.rs b/src/expr.rs
index 46046c8b0f..0f1a6953e2 100644
--- a/src/expr.rs
+++ b/src/expr.rs
@@ -965,6 +965,7 @@ pub(crate) mod parsing {
     use std::cmp::Ordering;
 
     mod kw {
+        crate::custom_keyword!(builtin);
         crate::custom_keyword!(raw);
     }
 
@@ -1594,6 +1595,8 @@ pub(crate) mod parsing {
             || input.peek(Token![async]) && (input.peek2(Token![|]) || input.peek2(Token![move]))
         {
             expr_closure(input, allow_struct).map(Expr::Closure)
+        } else if input.peek(kw::builtin) && input.peek2(Token![#]) {
+            expr_builtin(input)
         } else if input.peek(Ident)
             || input.peek(Token![::])
             || input.peek(Token![<])
@@ -1692,6 +1695,21 @@ pub(crate) mod parsing {
         }
     }
 
+    #[cfg(feature = "full")]
+    fn expr_builtin(input: ParseStream) -> Result<Expr> {
+        let begin = input.fork();
+
+        input.parse::<kw::builtin>()?;
+        input.parse::<Token![#]>()?;
+        input.parse::<Ident>()?;
+
+        let args;
+        parenthesized!(args in input);
+        args.parse::<TokenStream>()?;
+
+        Ok(Expr::Verbatim(verbatim::between(begin, input)))
+    }
+
     fn path_or_macro_or_struct(
         input: ParseStream,
         #[cfg(feature = "full")] allow_struct: AllowStruct,