try gating early, add non-ascii test

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -1,4 +1,3 @@
-use ast::token;
 use rustc_ast as ast;
 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
 use rustc_ast::{attr, AssocConstraint, AssocConstraintKind, NodeId};

compiler/rustc_parse/src/parser/expr.rs

@@ -1922,6 +1922,7 @@ pub(super) fn parse_opt_token_lit(&mut self) -> Option<(token::Lit, Span)> {
         let recovered = self.recover_after_dot();
         let token = recovered.as_ref().unwrap_or(&self.token);
         let span = token.span;
+
         token::Lit::from_token(token).map(|token_lit| {
             self.bump();
             (token_lit, span)

tests/ui/rfcs/rfc-3348-c-string-literals/non-ascii.rs

@@ -0,0 +1,10 @@
+// run-pass
+
+#![feature(c_str_literals)]
+
+fn main() {
+    assert_eq!(
+        c"\xEF\x80🦀\u{1F980}".to_bytes_with_nul(),
+        &[0xEF, 0x80, 0xF0, 0x9F, 0xA6, 0x80, 0xF0, 0x9F, 0xA6, 0x80, 0x00],
+    );
+}