[clang][parser] Allow GNU-style attributes in explicit template...

... instantiations

They are currently not being diagnosed because ProhibitAttributes() does
not handle attribute lists with an invalid source range. But once it
does, we need to allow GNU attributes in this place.

Additionally, start optionally diagnosing empty attr lists in
ProhibitCXX11Attributes(), since ProhibitAttribute() does it.

Differential Revision: https://reviews.llvm.org/D97362

1 files changed, 26 insertions, 2 deletions

diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index a044fbc..104b1b5 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -1607,7 +1607,30 @@ void Parser::DiagnoseProhibitedAttributes(
 }
 
 void Parser::ProhibitCXX11Attributes(ParsedAttributesWithRange &Attrs,
-                                     unsigned DiagID) {
+                                     unsigned DiagID, bool DiagnoseEmptyAttrs) {
+
+  if (DiagnoseEmptyAttrs && Attrs.empty() && Attrs.Range.isValid()) {
+    // An attribute list has been parsed, but it was empty.
+    // This is the case for [[]].
+    const auto &LangOpts = getLangOpts();
+    auto &SM = PP.getSourceManager();
+    Token FirstLSquare;
+    Lexer::getRawToken(Attrs.Range.getBegin(), FirstLSquare, SM, LangOpts);
+
+    if (FirstLSquare.is(tok::l_square)) {
+      llvm::Optional<Token> SecondLSquare =
+          Lexer::findNextToken(FirstLSquare.getLocation(), SM, LangOpts);
+
+      if (SecondLSquare && SecondLSquare->is(tok::l_square)) {
+        // The attribute range starts with [[, but is empty. So this must
+        // be [[]], which we are supposed to diagnose because
+        // DiagnoseEmptyAttrs is true.
+        Diag(Attrs.Range.getBegin(), DiagID) << Attrs.Range;
+        return;
+      }
+    }
+  }
+
   for (const ParsedAttr &AL : Attrs) {
     if (!AL.isCXX11Attribute() && !AL.isC2xAttribute())
       continue;
@@ -4630,7 +4653,8 @@ void Parser::ParseEnumSpecifier(SourceLocation StartLoc, DeclSpec &DS,
   // or opaque-enum-declaration anywhere.
   if (IsElaboratedTypeSpecifier && !getLangOpts().MicrosoftExt &&
       !getLangOpts().ObjC) {
-    ProhibitAttributes(attrs);
+    ProhibitCXX11Attributes(attrs, diag::err_attributes_not_allowed,
+                            /*DiagnoseEmptyAttrs=*/true);
     if (BaseType.isUsable())
       Diag(BaseRange.getBegin(), diag::ext_enum_base_in_type_specifier)
           << (AllowEnumSpecifier == AllowDefiningTypeSpec::Yes) << BaseRange;