fix: Ensure incremental compilation is also enabled

Author: futile

compiler/rustc_expand/src/proc_macro.rs

@@ -149,7 +149,11 @@ impl MultiItemModifier for DeriveProcMacro {
 
             let res = crate::derive_macro_expansion::enter_context((ecx, self.client), move || {
                 let key = (invoc_id, proc_macro_crate_hash, input);
-                if tcx.sess.opts.unstable_opts.cache_all_derive_macros {
+                // FIXME(pr-time): Is this the correct way to check for incremental compilation (as
+                // well)?
+                if tcx.sess.opts.incremental.is_some()
+                    && tcx.sess.opts.unstable_opts.cache_all_derive_macros
+                {
                     tcx.derive_macro_expansion(key).cloned()
                 } else {
                     crate::derive_macro_expansion::provide_derive_macro_expansion(tcx, key).cloned()