commit f63adf5b67f7a25b15f81d3a1a207aba4f226dc4
Author: Nico Weber <thakis@chromium.org>
Date:   Fri May 28 14:49:18 2021 -0400

    Revert "[clang][Parse] Add parsing support for C++ attributes on using-declarations"
    
    This reverts commit dc672999a9b12a156991891dc400308b52d569ba.
    Breaks check-clang everywhere, see https://reviews.llvm.org/D91630

diff --git a/clang/docs/LanguageExtensions.rst b/clang/docs/LanguageExtensions.rst
index c60b8b39e1c9..129e73345b2a 100644
--- a/clang/docs/LanguageExtensions.rst
+++ b/clang/docs/LanguageExtensions.rst
@@ -632,20 +632,6 @@ Attributes on the ``enum`` declaration do not apply to individual enumerators.
 
 Query for this feature with ``__has_extension(enumerator_attributes)``.
 
-C++11 Attributes on using-declarations
-======================================
-
-Clang allows C++-style ``[[]]`` attributes to be written on using-declarations.
-For instance:
-
-.. code-block:: c++
-
-  [[clang::using_if_exists]] using foo::bar;
-  using foo::baz [[clang::using_if_exists]];
-
-You can test for support for this extension with
-``__has_extension(cxx_attributes_on_using_declarations)``.
-
 'User-Specified' System Frameworks
 ==================================
 
diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index b43300ad6646..81609fa6efdf 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -113,9 +113,6 @@ Attribute Changes in Clang
 
 - ...
 
-- Added support for C++11-style ``[[]]`` attributes on using-declarations, as a
-  clang extension.
-
 Windows Support
 ---------------
 
diff --git a/clang/include/clang/Basic/DiagnosticParseKinds.td b/clang/include/clang/Basic/DiagnosticParseKinds.td
index 6d5d08e5fbad..97cb7020f345 100644
--- a/clang/include/clang/Basic/DiagnosticParseKinds.td
+++ b/clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -693,9 +693,6 @@ def ext_using_attribute_ns : ExtWarn<
 def err_using_attribute_ns_conflict : Error<
   "attribute with scope specifier cannot follow default scope specifier">;
 def err_attributes_not_allowed : Error<"an attribute list cannot appear here">;
-def ext_cxx11_attr_placement : ExtWarn<
-  "ISO C++ does not allow an attribute list to appear here">,
-  InGroup<DiagGroup<"cxx-attribute-extension">>;
 def err_attributes_misplaced : Error<"misplaced attributes; expected attributes here">;
 def err_l_square_l_square_not_attribute : Error<
   "C++11 only allows consecutive left square brackets when "
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 80130c2584fe..4b653b8b4737 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3957,9 +3957,6 @@ def warn_attribute_sentinel_named_arguments : Warning<
 def warn_attribute_sentinel_not_variadic : Warning<
   "'sentinel' attribute only supported for variadic %select{functions|blocks}0">,
   InGroup<IgnoredAttributes>;
-def warn_deprecated_ignored_on_using : Warning<
-  "%0 currently has no effect on a using declaration">,
-  InGroup<IgnoredAttributes>;
 def err_attribute_sentinel_less_than_zero : Error<
   "'sentinel' parameter 1 less than zero">;
 def err_attribute_sentinel_not_zero_or_one : Error<
diff --git a/clang/include/clang/Basic/Features.def b/clang/include/clang/Basic/Features.def
index 592e3e33baf1..a7a5e06a937e 100644
--- a/clang/include/clang/Basic/Features.def
+++ b/clang/include/clang/Basic/Features.def
@@ -259,7 +259,6 @@ EXTENSION(gnu_asm, LangOpts.GNUAsm)
 EXTENSION(gnu_asm_goto_with_outputs, LangOpts.GNUAsm)
 EXTENSION(matrix_types, LangOpts.MatrixTypes)
 EXTENSION(matrix_types_scalar_division, true)
-EXTENSION(cxx_attributes_on_using_declarations, LangOpts.CPlusPlus11)
 
 FEATURE(cxx_abi_relative_vtable, LangOpts.CPlusPlus && LangOpts.RelativeCXXABIVTables)
 
diff --git a/clang/include/clang/Parse/Parser.h b/clang/include/clang/Parse/Parser.h
index cb618d172c5b..e3e6509b025e 100644
--- a/clang/include/clang/Parse/Parser.h
+++ b/clang/include/clang/Parse/Parser.h
@@ -2634,10 +2634,6 @@ private:
   /// locations where attributes are not allowed.
   void DiagnoseAndSkipCXX11Attributes();
 
-  /// Emit warnings for C++11 and C2x attributes that are in a position that
-  /// clang accepts as an extension.
-  void DiagnoseCXX11AttributeExtension(ParsedAttributesWithRange &Attrs);
-
   /// Parses syntax-generic attribute arguments for attributes which are
   /// known to the implementation, and adds them to the given ParsedAttributes
   /// list with the given attribute syntax. Returns the number of arguments
@@ -3063,7 +3059,6 @@ private:
                                        const ParsedTemplateInfo &TemplateInfo,
                                        SourceLocation UsingLoc,
                                        SourceLocation &DeclEnd,
-                                       ParsedAttributesWithRange &Attrs,
                                        AccessSpecifier AS = AS_none);
   Decl *ParseAliasDeclarationAfterDeclarator(
       const ParsedTemplateInfo &TemplateInfo, SourceLocation UsingLoc,
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 76d031b62e9d..fda427508c05 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -1650,13 +1650,6 @@ void Parser::ProhibitCXX11Attributes(ParsedAttributesWithRange &Attrs,
   }
 }
 
-void Parser::DiagnoseCXX11AttributeExtension(ParsedAttributesWithRange &Attrs) {
-  for (const ParsedAttr &PA : Attrs) {
-    if (PA.isCXX11Attribute() || PA.isC2xAttribute())
-      Diag(PA.getLoc(), diag::ext_cxx11_attr_placement) << PA << PA.getRange();
-  }
-}
-
 // Usually, `__attribute__((attrib)) class Foo {} var` means that attribute
 // applies to var, not the type Foo.
 // As an exception to the rule, __declspec(align(...)) before the
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index 1d7b953a627b..af3d0df53e91 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -497,7 +497,11 @@ Parser::ParseUsingDirectiveOrDeclaration(DeclaratorContext Context,
   }
 
   // Otherwise, it must be a using-declaration or an alias-declaration.
-  return ParseUsingDeclaration(Context, TemplateInfo, UsingLoc, DeclEnd, attrs,
+
+  // Using declarations can't have attributes.
+  ProhibitAttributes(attrs);
+
+  return ParseUsingDeclaration(Context, TemplateInfo, UsingLoc, DeclEnd,
                                AS_none);
 }
 
@@ -623,8 +627,7 @@ bool Parser::ParseUsingDeclarator(DeclaratorContext Context,
   if (getLangOpts().CPlusPlus11 && Context == DeclaratorContext::Member &&
       Tok.is(tok::identifier) &&
       (NextToken().is(tok::semi) || NextToken().is(tok::comma) ||
-       NextToken().is(tok::ellipsis) || NextToken().is(tok::l_square) ||
-       NextToken().is(tok::kw___attribute)) &&
+       NextToken().is(tok::ellipsis)) &&
       D.SS.isNotEmpty() && LastII == Tok.getIdentifierInfo() &&
       !D.SS.getScopeRep()->getAsNamespace() &&
       !D.SS.getScopeRep()->getAsNamespaceAlias()) {
@@ -667,10 +670,11 @@ bool Parser::ParseUsingDeclarator(DeclaratorContext Context,
 ///     alias-declaration: C++11 [dcl.dcl]p1
 ///       'using' identifier attribute-specifier-seq[opt] = type-id ;
 ///
-Parser::DeclGroupPtrTy Parser::ParseUsingDeclaration(
-    DeclaratorContext Context, const ParsedTemplateInfo &TemplateInfo,
-    SourceLocation UsingLoc, SourceLocation &DeclEnd,
-    ParsedAttributesWithRange &PrefixAttrs, AccessSpecifier AS) {
+Parser::DeclGroupPtrTy
+Parser::ParseUsingDeclaration(DeclaratorContext Context,
+                              const ParsedTemplateInfo &TemplateInfo,
+                              SourceLocation UsingLoc, SourceLocation &DeclEnd,
+                              AccessSpecifier AS) {
   // Check for misplaced attributes before the identifier in an
   // alias-declaration.
   ParsedAttributesWithRange MisplacedAttrs(AttrFactory);
@@ -682,17 +686,6 @@ Parser::DeclGroupPtrTy Parser::ParseUsingDeclaration(
   ParsedAttributesWithRange Attrs(AttrFactory);
   MaybeParseAttributes(PAKM_GNU | PAKM_CXX11, Attrs);
 
-  // If we had any misplaced attributes from earlier, this is where they
-  // should have been written.
-  if (MisplacedAttrs.Range.isValid()) {
-    Diag(MisplacedAttrs.Range.getBegin(), diag::err_attributes_not_allowed)
-        << FixItHint::CreateInsertionFromRange(
-               Tok.getLocation(),
-               CharSourceRange::getTokenRange(MisplacedAttrs.Range))
-        << FixItHint::CreateRemoval(MisplacedAttrs.Range);
-    Attrs.takeAllFrom(MisplacedAttrs);
-  }
-
   // Maybe this is an alias-declaration.
   if (Tok.is(tok::equal)) {
     if (InvalidDeclarator) {
@@ -700,7 +693,16 @@ Parser::DeclGroupPtrTy Parser::ParseUsingDeclaration(
       return nullptr;
     }
 
-    ProhibitAttributes(PrefixAttrs);
+    // If we had any misplaced attributes from earlier, this is where they
+    // should have been written.
+    if (MisplacedAttrs.Range.isValid()) {
+      Diag(MisplacedAttrs.Range.getBegin(), diag::err_attributes_not_allowed)
+        << FixItHint::CreateInsertionFromRange(
+               Tok.getLocation(),
+               CharSourceRange::getTokenRange(MisplacedAttrs.Range))
+        << FixItHint::CreateRemoval(MisplacedAttrs.Range);
+      Attrs.takeAllFrom(MisplacedAttrs);
+    }
 
     Decl *DeclFromDeclSpec = nullptr;
     Decl *AD = ParseAliasDeclarationAfterDeclarator(
@@ -708,7 +710,10 @@ Parser::DeclGroupPtrTy Parser::ParseUsingDeclaration(
     return Actions.ConvertDeclToDeclGroup(AD, DeclFromDeclSpec);
   }
 
-  DiagnoseCXX11AttributeExtension(PrefixAttrs);
+  // C++11 attributes are not allowed on a using-declaration, but GNU ones
+  // are.
+  ProhibitAttributes(MisplacedAttrs);
+  ProhibitAttributes(Attrs);
 
   // Diagnose an attempt to declare a templated using-declaration.
   // In C++11, alias-declarations can be templates:
@@ -726,10 +731,8 @@ Parser::DeclGroupPtrTy Parser::ParseUsingDeclaration(
 
   SmallVector<Decl *, 8> DeclsInGroup;
   while (true) {
-    // Parse (optional) attributes.
-    MaybeParseAttributes(PAKM_GNU | PAKM_CXX11, Attrs);
-    DiagnoseCXX11AttributeExtension(Attrs);
-    Attrs.addAll(PrefixAttrs.begin(), PrefixAttrs.end());
+    // Parse (optional) attributes (most likely GNU strong-using extension).
+    MaybeParseGNUAttributes(Attrs);
 
     if (InvalidDeclarator)
       SkipUntil(tok::comma, tok::semi, StopBeforeMatch);
@@ -2615,6 +2618,8 @@ Parser::ParseCXXClassMemberDeclaration(AccessSpecifier AS,
   MaybeParseMicrosoftAttributes(attrs);
 
   if (Tok.is(tok::kw_using)) {
+    ProhibitAttributes(attrs);
+
     // Eat 'using'.
     SourceLocation UsingLoc = ConsumeToken();
 
@@ -2633,7 +2638,7 @@ Parser::ParseCXXClassMemberDeclaration(AccessSpecifier AS,
     SourceLocation DeclEnd;
     // Otherwise, it must be a using-declaration or an alias-declaration.
     return ParseUsingDeclaration(DeclaratorContext::Member, TemplateInfo,
-                                 UsingLoc, DeclEnd, attrs, AS);
+                                 UsingLoc, DeclEnd, AS);
   }
 
   // Hold late-parsed attributes so we can attach a Decl to them later.
diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
index 130ec7675820..65467a828a5a 100644
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -2446,13 +2446,6 @@ AvailabilityAttr *Sema::mergeAvailabilityAttr(
 }
 
 static void handleAvailabilityAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
-  if (isa<UsingDecl, UnresolvedUsingTypenameDecl, UnresolvedUsingValueDecl>(
-          D)) {
-    S.Diag(AL.getRange().getBegin(), diag::warn_deprecated_ignored_on_using)
-        << AL;
-    return;
-  }
-
   if (!AL.checkExactlyNumArgs(S, 1))
     return;
   IdentifierLoc *Platform = AL.getArgAsIdent(0);
@@ -7264,11 +7257,6 @@ static void handleDeprecatedAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
       // namespace.
       return;
     }
-  } else if (isa<UsingDecl, UnresolvedUsingTypenameDecl,
-                 UnresolvedUsingValueDecl>(D)) {
-    S.Diag(AL.getRange().getBegin(), diag::warn_deprecated_ignored_on_using)
-        << AL;
-    return;
   }
 
   // Handle the cases where the attribute has a text message.
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 7739625c1b9f..f4d8f4d9aa33 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -12071,9 +12071,9 @@ NamedDecl *Sema::BuildUsingDeclaration(
     return nullptr;
 
   DeclContext *LookupContext = computeDeclContext(SS);
+  NamedDecl *D;
   NestedNameSpecifierLoc QualifierLoc = SS.getWithLocInContext(Context);
   if (!LookupContext || EllipsisLoc.isValid()) {
-    NamedDecl *D;
     if (HasTypenameKeyword) {
       // FIXME: not all declaration name kinds are legal here
       D = UnresolvedUsingTypenameDecl::Create(Context, CurContext,
@@ -12087,7 +12087,6 @@ NamedDecl *Sema::BuildUsingDeclaration(
     }
     D->setAccess(AS);
     CurContext->addDecl(D);
-    ProcessDeclAttributeList(S, D, AttrList);
     return D;
   }
 
@@ -12097,7 +12096,6 @@ NamedDecl *Sema::BuildUsingDeclaration(
                           UsingName, HasTypenameKeyword);
     UD->setAccess(AS);
     CurContext->addDecl(UD);
-    ProcessDeclAttributeList(S, UD, AttrList);
     UD->setInvalidDecl(Invalid);
     return UD;
   };
diff --git a/clang/test/Parser/cxx0x-attributes.cpp b/clang/test/Parser/cxx0x-attributes.cpp
index 1b34c8cfd103..0b2bad6b0002 100644
--- a/clang/test/Parser/cxx0x-attributes.cpp
+++ b/clang/test/Parser/cxx0x-attributes.cpp
@@ -131,12 +131,12 @@ extern "C++" [[]] { } // expected-error {{an attribute list cannot appear here}}
 [[]] static_assert(true, ""); //expected-error {{an attribute list cannot appear here}}
 [[]] asm(""); // expected-error {{an attribute list cannot appear here}}
 
-[[]] using ns::i;
+[[]] using ns::i; // expected-error {{an attribute list cannot appear here}}
 [[unknown]] using namespace ns; // expected-warning {{unknown attribute 'unknown' ignored}}
 [[noreturn]] using namespace ns; // expected-error {{'noreturn' attribute only applies to functions}}
 namespace [[]] ns2 {} // expected-warning {{attributes on a namespace declaration are a C++17 extension}}
 
-using[[]] alignas(4)[[]] ns::i;          // expected-error {{an attribute list cannot appear here}} expected-error {{'alignas' attribute only applies to variables, data members and tag types}} expected-warning {{ISO C++}}
+using [[]] alignas(4) [[]] ns::i; // expected-error {{an attribute list cannot appear here}}
 using [[]] alignas(4) [[]] foobar = int; // expected-error {{an attribute list cannot appear here}} expected-error {{'alignas' attribute only applies to}}
 
 void bad_attributes_in_do_while() {
@@ -157,16 +157,7 @@ void bad_attributes_in_do_while() {
 [[]] using T = int; // expected-error {{an attribute list cannot appear here}}
 using T [[]] = int; // ok
 template<typename T> using U [[]] = T;
-using ns::i [[]];
-using ns::i [[]], ns::i [[]]; // expected-warning {{use of multiple declarators in a single using declaration is a C++17 extension}}
-struct using_in_struct_base {
-  typedef int i, j, k, l;
-};
-struct using_in_struct : using_in_struct_base {
-  [[]] using using_in_struct_base::i;
-  using using_in_struct_base::j [[]];
-  [[]] using using_in_struct_base::k [[]], using_in_struct_base::l [[]]; // expected-warning {{use of multiple declarators in a single using declaration is a C++17 extension}}
-};
+using ns::i [[]]; // expected-error {{an attribute list cannot appear here}}
 using [[]] ns::i; // expected-error {{an attribute list cannot appear here}}
 using T [[unknown]] = int; // expected-warning {{unknown attribute 'unknown' ignored}}
 using T [[noreturn]] = int; // expected-error {{'noreturn' attribute only applies to functions}}
diff --git a/clang/test/SemaCXX/cxx11-attributes-on-using-declaration.cpp b/clang/test/SemaCXX/cxx11-attributes-on-using-declaration.cpp
deleted file mode 100644
index 0377a5920358..000000000000
--- a/clang/test/SemaCXX/cxx11-attributes-on-using-declaration.cpp
+++ /dev/null
@@ -1,42 +0,0 @@
-// RUN: %clang_cc1 -pedantic -triple x86_64-apple-macos11 -std=c++20 -fsyntax-only -verify %s
-
-static_assert(__has_extension(cxx_attributes_on_using_declarations), "");
-
-namespace NS { typedef int x; }
-
-[[clang::annotate("foo")]] using NS::x; // expected-warning{{ISO C++ does not allow an attribute list to appear here}}
-
-
-[[deprecated]] using NS::x;                                    // expected-warning {{'deprecated' currently has no effect on using-declarations}} expected-warning{{ISO C++ does not allow}}
-using NS::x [[deprecated]];                                    // expected-warning {{'deprecated' currently has no effect on using-declarations}} expected-warning{{ISO C++ does not allow}}
-using NS::x __attribute__((deprecated));                       // expected-warning {{'deprecated' currently has no effect on using-declarations}}
-using NS::x __attribute__((availability(macos,introduced=1))); // expected-warning {{'availability' currently has no effect on using-declarations}}
-
-[[clang::availability(macos,introduced=1)]] using NS::x; // expected-warning {{'availability' currently has no effect on using-declarations}} expected-warning{{ISO C++ does not allow}}
-
-// expected-warning@+1 3 {{ISO C++ does not allow an attribute list to appear here}}
-[[clang::annotate("A")]] using NS::x [[clang::annotate("Y")]], NS::x [[clang::annotate("Z")]];
-
-template <class T>
-struct S : T {
-  [[deprecated]] using typename T::x; // expected-warning{{ISO C++ does not allow}} expected-warning {{'deprecated' currently has no effect on using-declarations}}
-  [[deprecated]] using T::y;          // expected-warning{{ISO C++ does not allow}} expected-warning {{'deprecated' currently has no effect on using-declarations}}
-
-  using typename T::z [[deprecated]]; // expected-warning{{ISO C++ does not allow}} expected-warning {{'deprecated' currently has no effect on using-declarations}}
-  using T::a [[deprecated]];          // expected-warning{{ISO C++ does not allow}} expected-warning {{'deprecated' currently has no effect on using-declarations}}
-};
-
-struct Base {};
-
-template <class B>
-struct DepBase1 : B {
-  using B::B [[]];
-
-};
-template <class B>
-struct DepBase2 : B {
-  using B::B __attribute__(());
-};
-
-DepBase1<Base> db1;
-DepBase2<Base> db2;