Auto merge of #54093 - petrochenkov:noinner, r=alexcrichton

Feature gate non-builtin attributes in inner attribute position

Closes item 3 from https://github.com/rust-lang/rust/pull/50911#issuecomment-411605393

2 files changed, 26 insertions, 8 deletions

diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 3bb19121ee3..7b4e1814a33 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -1074,6 +1074,21 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
         self.collect(kind, InvocationKind::Attr { attr, traits, item })
     }
 
+    fn find_attr_invoc(&self, attrs: &mut Vec<ast::Attribute>) -> Option<ast::Attribute> {
+        let attr = attrs.iter()
+                        .position(|a| !attr::is_known(a) && !is_builtin_attr(a))
+                        .map(|i| attrs.remove(i));
+        if let Some(attr) = &attr {
+            if !self.cx.ecfg.enable_custom_inner_attributes() &&
+               attr.style == ast::AttrStyle::Inner && attr.path != "test" {
+                emit_feature_err(&self.cx.parse_sess, "custom_inner_attributes",
+                                 attr.span, GateIssue::Language,
+                                 "non-builtin inner attributes are unstable");
+            }
+        }
+        attr
+    }
+
     /// If `item` is an attr invocation, remove and return the macro attribute and derive traits.
     fn classify_item<T>(&mut self, mut item: T) -> (Option<ast::Attribute>, Vec<Path>, T)
         where T: HasAttrs,
@@ -1087,7 +1102,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                 return attrs;
             }
 
-            attr = find_attr_invoc(&mut attrs);
+            attr = self.find_attr_invoc(&mut attrs);
             traits = collect_derives(&mut self.cx, &mut attrs);
             attrs
         });
@@ -1108,7 +1123,7 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                 return attrs;
             }
 
-            attr = find_attr_invoc(&mut attrs);
+            attr = self.find_attr_invoc(&mut attrs);
             attrs
         });
 
@@ -1145,12 +1160,6 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
     }
 }
 
-pub fn find_attr_invoc(attrs: &mut Vec<ast::Attribute>) -> Option<ast::Attribute> {
-    attrs.iter()
-         .position(|a| !attr::is_known(a) && !is_builtin_attr(a))
-         .map(|i| attrs.remove(i))
-}
-
 impl<'a, 'b> Folder for InvocationCollector<'a, 'b> {
     fn fold_expr(&mut self, expr: P<ast::Expr>) -> P<ast::Expr> {
         let mut expr = self.cfg.configure_expr(expr).into_inner();
@@ -1582,6 +1591,12 @@ impl<'feat> ExpansionConfig<'feat> {
         fn proc_macro_expr = proc_macro_expr,
         fn proc_macro_non_items = proc_macro_non_items,
     }
+
+    fn enable_custom_inner_attributes(&self) -> bool {
+        self.features.map_or(false, |features| {
+            features.custom_inner_attributes || features.custom_attribute || features.rustc_attrs
+        })
+    }
 }
 
 // A Marker adds the given mark to the syntax context.
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index e912482cf58..3e880bb6cf6 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -518,6 +518,9 @@ declare_features! (
     // #![test_runner]
     // #[test_case]
     (active, custom_test_frameworks, "1.30.0", Some(50297), None),
+
+    // Non-builtin attributes in inner attribute position
+    (active, custom_inner_attributes, "1.30.0", Some(38356), None),
 );
 
 declare_features! (