Auto merge of #34654 - jseyfried:configure_multi_modified, r=nrc

Perform `cfg` attribute processing on `MultiModifier`-generated items

Fixes https://users.rust-lang.org/t/unused-attribute-warning-for-custom-derive-attribute/6180.
r? @nrc

src/libsyntax/ext/expand.rs

@@ -769,7 +769,11 @@ fn expand_annotatable(mut item: Annotatable, fld: &mut MacroExpander) -> SmallVe
             };
 
             fld.cx.bt_pop();
-            modified.into_iter().flat_map(|it| expand_annotatable(it, fld)).collect()
+            let configured = modified.into_iter().flat_map(|it| {
+                it.fold_with(&mut fld.strip_unconfigured())
+            }).collect::<SmallVector<_>>();
+
+            configured.into_iter().flat_map(|it| expand_annotatable(it, fld)).collect()
         }
     }
 }

src/test/run-pass-fulldeps/auxiliary/macro_crate_test.rs

@@ -72,6 +72,7 @@ fn expand_into_foo_multi(cx: &mut ExtCtxt,
                 ..(*quote_item!(cx, enum Foo2 { Bar2, Baz2 }).unwrap()).clone()
             })),
             Annotatable::Item(quote_item!(cx, enum Foo3 { Bar }).unwrap()),
+            Annotatable::Item(quote_item!(cx, #[cfg(any())] fn foo2() {}).unwrap()),
         ],
         Annotatable::ImplItem(it) => vec![
             quote_item!(cx, impl X { fn foo(&self) -> i32 { 42 } }).unwrap().and_then(|i| {

src/test/run-pass-fulldeps/macro-crate.rs

@@ -21,6 +21,9 @@ extern crate macro_crate_test;
 #[derive(PartialEq, Clone, Debug)]
 fn foo() -> AnotherFakeTypeThatHadBetterGoAway {}
 
+// Check that the `#[into_multi_foo]`-generated `foo2` is configured away
+fn foo2() {}
+
 trait Qux {
     #[into_multi_foo]
     fn bar();