mbe: Use unreachable!() for expand when we expect only expand_with_safety

Author: joshtriplett

compiler/rustc_expand/src/mbe/macro_rules.rs

@@ -250,23 +250,12 @@ impl TTMacroExpander for MacroRulesMacroExpander {
 impl AttrProcMacro for MacroRulesMacroExpander {
     fn expand(
         &self,
-        cx: &mut ExtCtxt<'_>,
-        sp: Span,
-        args: TokenStream,
-        body: TokenStream,
+        _cx: &mut ExtCtxt<'_>,
+        _sp: Span,
+        _args: TokenStream,
+        _body: TokenStream,
     ) -> Result<TokenStream, ErrorGuaranteed> {
-        expand_macro_attr(
-            cx,
-            sp,
-            self.span,
-            self.node_id,
-            self.name,
-            self.transparency,
-            Safety::Default,
-            args,
-            body,
-            &self.rules,
-        )
+        unreachable!("`expand` called on `MacroRulesMacroExpander`, expected `expand_with_safety`")
     }
 
     fn expand_with_safety(