Ban custom inner attributes in expressions and statements

compiler/rustc_expand/src/expand.rs

@@ -206,30 +206,36 @@ ast_fragments! {
     }
 }
 
+pub enum SupportsMacroExpansion {
+    No,
+    Yes { supports_inner_attrs: bool },
+}
+
 impl AstFragmentKind {
     crate fn dummy(self, span: Span) -> AstFragment {
         self.make_from(DummyResult::any(span)).expect("couldn't create a dummy AST fragment")
     }
 
-    /// Fragment supports macro expansion and not just inert attributes, `cfg` and `cfg_attr`.
-    pub fn supports_macro_expansion(self) -> bool {
+    pub fn supports_macro_expansion(self) -> SupportsMacroExpansion {
         match self {
             AstFragmentKind::OptExpr
             | AstFragmentKind::Expr
-            | AstFragmentKind::Pat
-            | AstFragmentKind::Ty
             | AstFragmentKind::Stmts
-            | AstFragmentKind::Items
+            | AstFragmentKind::Ty
+            | AstFragmentKind::Pat => SupportsMacroExpansion::Yes { supports_inner_attrs: false },
+            AstFragmentKind::Items
             | AstFragmentKind::TraitItems
             | AstFragmentKind::ImplItems
-            | AstFragmentKind::ForeignItems => true,
+            | AstFragmentKind::ForeignItems => {
+                SupportsMacroExpansion::Yes { supports_inner_attrs: true }
+            }
             AstFragmentKind::Arms
             | AstFragmentKind::Fields
             | AstFragmentKind::FieldPats
             | AstFragmentKind::GenericParams
             | AstFragmentKind::Params
             | AstFragmentKind::StructFields
-            | AstFragmentKind::Variants => false,
+            | AstFragmentKind::Variants => SupportsMacroExpansion::No,
         }
     }
 

compiler/rustc_resolve/src/macros.rs

@@ -17,7 +17,7 @@ use rustc_errors::struct_span_err;
 use rustc_expand::base::Annotatable;
 use rustc_expand::base::{Indeterminate, ResolverExpand, SyntaxExtension, SyntaxExtensionKind};
 use rustc_expand::compile_declarative_macro;
-use rustc_expand::expand::{AstFragment, Invocation, InvocationKind};
+use rustc_expand::expand::{AstFragment, Invocation, InvocationKind, SupportsMacroExpansion};
 use rustc_feature::is_builtin_attr_name;
 use rustc_hir::def::{self, DefKind, NonMacroAttrKind};
 use rustc_hir::def_id;
@@ -278,12 +278,12 @@ impl<'a> ResolverExpand for Resolver<'a> {
 
         // Derives are not included when `invocations` are collected, so we have to add them here.
         let parent_scope = &ParentScope { derives, ..parent_scope };
-        let require_inert = !invoc.fragment_kind.supports_macro_expansion();
+        let supports_macro_expansion = invoc.fragment_kind.supports_macro_expansion();
         let node_id = self.lint_node_id(eager_expansion_root);
         let (ext, res) = self.smart_resolve_macro_path(
             path,
             kind,
-            require_inert,
+            supports_macro_expansion,
             inner_attr,
             parent_scope,
             node_id,
@@ -457,7 +457,7 @@ impl<'a> Resolver<'a> {
         &mut self,
         path: &ast::Path,
         kind: MacroKind,
-        require_inert: bool,
+        supports_macro_expansion: SupportsMacroExpansion,
         inner_attr: bool,
         parent_scope: &ParentScope<'a>,
         node_id: NodeId,
@@ -505,8 +505,17 @@ impl<'a> Resolver<'a> {
 
         let unexpected_res = if ext.macro_kind() != kind {
             Some((kind.article(), kind.descr_expected()))
-        } else if require_inert && matches!(res, Res::Def(..)) {
-            Some(("a", "non-macro attribute"))
+        } else if matches!(res, Res::Def(..)) {
+            match supports_macro_expansion {
+                SupportsMacroExpansion::No => Some(("a", "non-macro attribute")),
+                SupportsMacroExpansion::Yes { supports_inner_attrs } => {
+                    if inner_attr && !supports_inner_attrs {
+                        Some(("a", "non-macro inner attribute"))
+                    } else {
+                        None
+                    }
+                }
+            }
         } else {
             None
         };