rustc_parse: Make Parser::unexpected public and use it in built-in macros

compiler/rustc_builtin_macros/src/asm.rs

@@ -164,7 +164,7 @@ fn parse_args<'a>(
             args.templates.push(template);
             continue;
         } else {
-            return Err(p.expect_one_of(&[], &[]).unwrap_err());
+            return p.unexpected();
         };
 
         allow_templates = false;
@@ -348,7 +348,7 @@ fn parse_options<'a>(p: &mut Parser<'a>, args: &mut AsmArgs) -> Result<(), Diagn
         } else if p.eat_keyword(sym::att_syntax) {
             try_set_option(p, args, sym::att_syntax, ast::InlineAsmOptions::ATT_SYNTAX);
         } else {
-            return Err(p.expect_one_of(&[], &[]).unwrap_err());
+            return p.unexpected();
         }
 
         // Allow trailing commas

compiler/rustc_builtin_macros/src/assert.rs

@@ -120,8 +120,7 @@ fn parse_assert<'a>(
         };
 
     if parser.token != token::Eof {
-        parser.expect_one_of(&[], &[])?;
-        unreachable!();
+        return parser.unexpected();
     }
 
     Ok(Assert { cond_expr, custom_message })

compiler/rustc_parse/src/parser/mod.rs

@@ -386,7 +386,7 @@ fn next_tok(&mut self, fallback_span: Span) -> Token {
         next
     }
 
-    crate fn unexpected<T>(&mut self) -> PResult<'a, T> {
+    pub fn unexpected<T>(&mut self) -> PResult<'a, T> {
         match self.expect_one_of(&[], &[]) {
             Err(e) => Err(e),
             // We can get `Ok(true)` from `recover_closing_delimiter`