builtin_macros: Make #[derive(A, B, ...)] cfg-eval its input only for A, B, ...

Author: petrochenkov

compiler/rustc_builtin_macros/src/derive.rs

@@ -26,7 +26,7 @@ impl MultiItemModifier for Expander {
             return ExpandResult::Ready(vec![item]);
         }
 
-        let item = cfg_eval(ecx, item);
+        let configured_item = cfg_eval(ecx, item.clone());
 
         let result =
             ecx.resolver.resolve_derives(ecx.current_expansion.id, ecx.force_mode, &|| {
@@ -56,7 +56,7 @@ impl MultiItemModifier for Expander {
                         report_path_args(sess, &meta);
                         meta.path
                     })
-                    .map(|path| (path, item.clone(), None))
+                    .map(|path| (path, configured_item.clone(), None))
                     .collect()
             });
 

src/test/ui/proc-macro/attribute-after-derive.stdout

@@ -130,7 +130,7 @@ PRINT-DERIVE INPUT (DEBUG): TokenStream [
         span: $DIR/attribute-after-derive.rs:25:24: 28:2 (#0),
     },
 ]
-PRINT-ATTR INPUT (DISPLAY): struct DeriveAttribute { }
+PRINT-ATTR INPUT (DISPLAY): struct DeriveAttribute { #[cfg(FALSE)] field : u8, }
 PRINT-ATTR INPUT (DEBUG): TokenStream [
     Ident {
         ident: "struct",
@@ -142,7 +142,51 @@ PRINT-ATTR INPUT (DEBUG): TokenStream [
     },
     Group {
         delimiter: Brace,
-        stream: TokenStream [],
+        stream: TokenStream [
+            Punct {
+                ch: '#',
+                spacing: Alone,
+                span: $DIR/attribute-after-derive.rs:26:5: 26:6 (#0),
+            },
+            Group {
+                delimiter: Bracket,
+                stream: TokenStream [
+                    Ident {
+                        ident: "cfg",
+                        span: $DIR/attribute-after-derive.rs:26:7: 26:10 (#0),
+                    },
+                    Group {
+                        delimiter: Parenthesis,
+                        stream: TokenStream [
+                            Ident {
+                                ident: "FALSE",
+                                span: $DIR/attribute-after-derive.rs:26:11: 26:16 (#0),
+                            },
+                        ],
+                        span: $DIR/attribute-after-derive.rs:26:10: 26:17 (#0),
+                    },
+                ],
+                span: $DIR/attribute-after-derive.rs:26:6: 26:18 (#0),
+            },
+            Ident {
+                ident: "field",
+                span: $DIR/attribute-after-derive.rs:27:5: 27:10 (#0),
+            },
+            Punct {
+                ch: ':',
+                spacing: Alone,
+                span: $DIR/attribute-after-derive.rs:27:10: 27:11 (#0),
+            },
+            Ident {
+                ident: "u8",
+                span: $DIR/attribute-after-derive.rs:27:12: 27:14 (#0),
+            },
+            Punct {
+                ch: ',',
+                spacing: Alone,
+                span: $DIR/attribute-after-derive.rs:27:14: 27:15 (#0),
+            },
+        ],
         span: $DIR/attribute-after-derive.rs:25:24: 28:2 (#0),
     },
 ]