From 596f76a799c933927eec4d8ac8a83c44efff9854 Mon Sep 17 00:00:00 2001
From: Yingchi Long <i@lyc.dev>
Date: Mon, 16 Jan 2023 16:52:50 +0800
Subject: [PATCH] Revert "[C2x] reject type definitions in offsetof"

This reverts commit e327b52766ed497e4779f4e652b9ad237dfda8e6.
---
 clang/docs/ReleaseNotes.rst                   |  3 -
 .../clang/Basic/DiagnosticSemaKinds.td        |  2 -
 clang/include/clang/Parse/Parser.h            |  3 -
 .../clang/Parse/RAIIObjectsForParser.h        | 13 ----
 clang/include/clang/Sema/Sema.h               | 12 +---
 clang/lib/Parse/ParseDecl.cpp                 |  2 +-
 clang/lib/Parse/ParseDeclCXX.cpp              |  2 +-
 clang/lib/Parse/ParseExpr.cpp                 | 19 ++----
 clang/lib/Sema/SemaDecl.cpp                   | 12 +---
 clang/lib/Sema/SemaDeclCXX.cpp                |  6 +-
 clang/lib/Sema/SemaTemplate.cpp               | 13 ++--
 clang/test/C/C2x/n2350.c                      | 67 -------------------
 clang/test/C/drs/dr4xx.c                      |  7 +-
 clang/test/Parser/declarators.c               |  4 ++
 clang/test/SemaCXX/offsetof.cpp               | 17 -----
 15 files changed, 28 insertions(+), 154 deletions(-)
 delete mode 100644 clang/test/C/C2x/n2350.c

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index a75bc1df2d7c..09133f967f01 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -670,9 +670,6 @@ C2x Feature Support
       va_start(list); // Invalid in C17 and earlier, valid in C2x and later.
       va_end(list);
     }
-    
-- Reject type definitions in the ``type`` argument of ``__builtin_offsetof`` 
-  according to `WG14 N2350 <https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm>`_.
 
 C++ Language Changes in Clang
 -----------------------------
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 862ac845bda4..02afb098b239 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -1650,8 +1650,6 @@ def err_type_defined_in_condition : Error<
   "%0 cannot be defined in a condition">;
 def err_type_defined_in_enum : Error<
   "%0 cannot be defined in an enumeration">;
-def err_type_defined_in_offsetof : Error<
-  "%0 cannot be defined in '%select{__builtin_offsetof|offsetof}1'">;
 
 def note_pure_virtual_function : Note<
   "unimplemented pure virtual method %0 in %1">;
diff --git a/clang/include/clang/Parse/Parser.h b/clang/include/clang/Parse/Parser.h
index 6f9581b9ea1f..7a33532eec14 100644
--- a/clang/include/clang/Parse/Parser.h
+++ b/clang/include/clang/Parse/Parser.h
@@ -62,7 +62,6 @@ class Parser : public CodeCompletionHandler {
   friend class ColonProtectionRAIIObject;
   friend class ParsingOpenMPDirectiveRAII;
   friend class InMessageExpressionRAIIObject;
-  friend class OffsetOfStateRAIIObject;
   friend class PoisonSEHIdentifiersRAIIObject;
   friend class ObjCDeclContextSwitch;
   friend class ParenBraceBracketBalancer;
@@ -249,8 +248,6 @@ class Parser : public CodeCompletionHandler {
   /// function call.
   bool CalledSignatureHelp = false;
 
-  Sema::OffsetOfKind OffsetOfState = Sema::OffsetOfKind::OOK_Outside;
-
   /// The "depth" of the template parameters currently being parsed.
   unsigned TemplateParameterDepth;
 
diff --git a/clang/include/clang/Parse/RAIIObjectsForParser.h b/clang/include/clang/Parse/RAIIObjectsForParser.h
index cb525c9d0edd..5ae609e60073 100644
--- a/clang/include/clang/Parse/RAIIObjectsForParser.h
+++ b/clang/include/clang/Parse/RAIIObjectsForParser.h
@@ -341,19 +341,6 @@ namespace clang {
     }
   };
 
-  class OffsetOfStateRAIIObject {
-    Sema::OffsetOfKind &OffsetOfState;
-    Sema::OffsetOfKind OldValue;
-
-  public:
-    OffsetOfStateRAIIObject(Parser &P, Sema::OffsetOfKind Value)
-        : OffsetOfState(P.OffsetOfState), OldValue(P.OffsetOfState) {
-      OffsetOfState = Value;
-    }
-
-    ~OffsetOfStateRAIIObject() { OffsetOfState = OldValue; }
-  };
-
   /// RAII object that makes sure paren/bracket/brace count is correct
   /// after declaration/statement parsing, even when there's a parsing error.
   class ParenBraceBracketBalancer {
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index 35e319879a98..30c5ea608f7a 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -3304,16 +3304,6 @@ public:
     TUK_Friend       // Friend declaration:  'friend struct foo;'
   };
 
-  enum OffsetOfKind {
-    // Not parsing a type within __builtin_offsetof.
-    OOK_Outside,
-    // Parsing a type within __builtin_offsetof.
-    OOK_Builtin,
-    // Parsing a type within macro "offsetof", defined in __buitin_offsetof
-    // To improve our diagnostic message.
-    OOK_Macro,
-  };
-
   Decl *ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
                  SourceLocation KWLoc, CXXScopeSpec &SS, IdentifierInfo *Name,
                  SourceLocation NameLoc, const ParsedAttributesView &Attr,
@@ -3322,7 +3312,7 @@ public:
                  bool &IsDependent, SourceLocation ScopedEnumKWLoc,
                  bool ScopedEnumUsesClassTag, TypeResult UnderlyingType,
                  bool IsTypeSpecifier, bool IsTemplateParamOrArg,
-                 OffsetOfKind OOK, SkipBodyInfo *SkipBody = nullptr);
+                 SkipBodyInfo *SkipBody = nullptr);
 
   Decl *ActOnTemplatedFriendTag(Scope *S, SourceLocation FriendLoc,
                                 unsigned TagSpec, SourceLocation TagLoc,
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 75937c0d6a95..56fe9c3ac7ba 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -4972,7 +4972,7 @@ void Parser::ParseEnumSpecifier(SourceLocation StartLoc, DeclSpec &DS,
       DSC == DeclSpecContext::DSC_type_specifier,
       DSC == DeclSpecContext::DSC_template_param ||
           DSC == DeclSpecContext::DSC_template_type_arg,
-      OffsetOfState, &SkipBody);
+      &SkipBody);
 
   if (SkipBody.ShouldSkip) {
     assert(TUK == Sema::TUK_Definition && "can only skip a definition");
diff --git a/clang/lib/Parse/ParseDeclCXX.cpp b/clang/lib/Parse/ParseDeclCXX.cpp
index 227c1df2bddd..5d721f48140f 100644
--- a/clang/lib/Parse/ParseDeclCXX.cpp
+++ b/clang/lib/Parse/ParseDeclCXX.cpp
@@ -2074,7 +2074,7 @@ void Parser::ParseClassSpecifier(tok::TokenKind TagTokKind,
         DSC == DeclSpecContext::DSC_type_specifier,
         DSC == DeclSpecContext::DSC_template_param ||
             DSC == DeclSpecContext::DSC_template_type_arg,
-        OffsetOfState, &SkipBody);
+        &SkipBody);
 
     // If ActOnTag said the type was dependent, try again with the
     // less common call.
diff --git a/clang/lib/Parse/ParseExpr.cpp b/clang/lib/Parse/ParseExpr.cpp
index e8bdf5f421af..b1bf988307b1 100644
--- a/clang/lib/Parse/ParseExpr.cpp
+++ b/clang/lib/Parse/ParseExpr.cpp
@@ -2592,21 +2592,10 @@ ExprResult Parser::ParseBuiltinPrimaryExpression() {
   }
   case tok::kw___builtin_offsetof: {
     SourceLocation TypeLoc = Tok.getLocation();
-    auto K = Sema::OffsetOfKind::OOK_Builtin;
-    if (Tok.getLocation().isMacroID()) {
-      StringRef MacroName = Lexer::getImmediateMacroNameForDiagnostics(
-          Tok.getLocation(), PP.getSourceManager(), getLangOpts());
-      if (MacroName == "offsetof")
-        K = Sema::OffsetOfKind::OOK_Macro;
-    }
-    TypeResult Ty;
-    {
-      OffsetOfStateRAIIObject InOffsetof(*this, K);
-      Ty = ParseTypeName();
-      if (Ty.isInvalid()) {
-        SkipUntil(tok::r_paren, StopAtSemi);
-        return ExprError();
-      }
+    TypeResult Ty = ParseTypeName();
+    if (Ty.isInvalid()) {
+      SkipUntil(tok::r_paren, StopAtSemi);
+      return ExprError();
     }
 
     if (ExpectAndConsume(tok::comma)) {
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 072bc9b5dc26..e3fd4045e8bb 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -16592,7 +16592,7 @@ Decl *Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
                      SourceLocation ScopedEnumKWLoc,
                      bool ScopedEnumUsesClassTag, TypeResult UnderlyingType,
                      bool IsTypeSpecifier, bool IsTemplateParamOrArg,
-                     OffsetOfKind OOK, SkipBodyInfo *SkipBody) {
+                     SkipBodyInfo *SkipBody) {
   // If this is not a definition, it must have a name.
   IdentifierInfo *OrigName = Name;
   assert((Name != nullptr || TUK == TUK_Definition) &&
@@ -17365,16 +17365,10 @@ CreateNewDecl:
                                cast_or_null<RecordDecl>(PrevDecl));
   }
 
-  if (OOK != OOK_Outside && TUK == TUK_Definition) {
-    Diag(New->getLocation(), diag::err_type_defined_in_offsetof)
-        << Context.getTagDeclType(New) << static_cast<int>(OOK == OOK_Macro);
-    Invalid = true;
-  }
-
   // C++11 [dcl.type]p3:
   //   A type-specifier-seq shall not define a class or enumeration [...].
-  if (!Invalid && getLangOpts().CPlusPlus &&
-      (IsTypeSpecifier || IsTemplateParamOrArg) && TUK == TUK_Definition) {
+  if (getLangOpts().CPlusPlus && (IsTypeSpecifier || IsTemplateParamOrArg) &&
+      TUK == TUK_Definition) {
     Diag(New->getLocation(), diag::err_type_defined_in_type_specifier)
       << Context.getTagDeclType(New);
     Invalid = true;
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index ea52b703b563..0d7e3e893878 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -16962,15 +16962,15 @@ Decl *Sema::ActOnTemplatedFriendTag(Scope *S, SourceLocation FriendLoc,
     if (SS.isEmpty()) {
       bool Owned = false;
       bool IsDependent = false;
-      return ActOnTag(S, TagSpec, TUK_Friend, TagLoc, SS, Name, NameLoc, Attr,
-                      AS_public,
+      return ActOnTag(S, TagSpec, TUK_Friend, TagLoc, SS, Name, NameLoc,
+                      Attr, AS_public,
                       /*ModulePrivateLoc=*/SourceLocation(),
                       MultiTemplateParamsArg(), Owned, IsDependent,
                       /*ScopedEnumKWLoc=*/SourceLocation(),
                       /*ScopedEnumUsesClassTag=*/false,
                       /*UnderlyingType=*/TypeResult(),
                       /*IsTypeSpecifier=*/false,
-                      /*IsTemplateParamOrArg=*/false, /*OOK=*/OOK_Outside);
+                      /*IsTemplateParamOrArg=*/false);
     }
 
     NestedNameSpecifierLoc QualifierLoc = SS.getWithLocInContext(Context);
diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 31c2bf5d8127..17f0d0263a3d 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -10181,12 +10181,13 @@ Sema::ActOnExplicitInstantiation(Scope *S, SourceLocation ExternLoc,
 
   bool Owned = false;
   bool IsDependent = false;
-  Decl *TagD = ActOnTag(
-      S, TagSpec, Sema::TUK_Reference, KWLoc, SS, Name, NameLoc, Attr, AS_none,
-      /*ModulePrivateLoc=*/SourceLocation(), MultiTemplateParamsArg(), Owned,
-      IsDependent, SourceLocation(), false, TypeResult(),
-      /*IsTypeSpecifier*/ false,
-      /*IsTemplateParamOrArg=*/false, /*OOK=*/OOK_Outside);
+  Decl *TagD = ActOnTag(S, TagSpec, Sema::TUK_Reference,
+                        KWLoc, SS, Name, NameLoc, Attr, AS_none,
+                        /*ModulePrivateLoc=*/SourceLocation(),
+                        MultiTemplateParamsArg(), Owned, IsDependent,
+                        SourceLocation(), false, TypeResult(),
+                        /*IsTypeSpecifier*/false,
+                        /*IsTemplateParamOrArg*/false);
   assert(!IsDependent && "explicit instantiation of dependent name not yet handled");
 
   if (!TagD)
diff --git a/clang/test/C/C2x/n2350.c b/clang/test/C/C2x/n2350.c
deleted file mode 100644
index 3b4bdec26bf7..000000000000
--- a/clang/test/C/C2x/n2350.c
+++ /dev/null
@@ -1,67 +0,0 @@
-// RUN: %clang_cc1 -fsyntax-only -verify %s
-// RUN: %clang_cc1 -fsyntax-only -std=c89 -verify %s
-// RUN: %clang_cc1 -fsyntax-only -std=c99 -verify %s
-// RUN: %clang_cc1 -fsyntax-only -std=c11 -verify %s
-// RUN: %clang_cc1 -fsyntax-only -std=c17 -verify %s
-// RUN: %clang_cc1 -fsyntax-only -std=c2x -verify %s
-
-// Reject definitions in __builtin_offsetof
-// https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm
-int simple(void) {
-  return __builtin_offsetof(struct A // expected-error{{'struct A' cannot be defined in '__builtin_offsetof'}} 
-  { 
-    int a;
-    struct B // expected-error{{'struct B' cannot be defined in '__builtin_offsetof'}} 
-    {
-      int c;
-      int d;
-    } x;
-  }, a);
-}
-
-int anonymous_struct() {
-  return __builtin_offsetof(struct // expected-error-re{{'struct (unnamed at {{.*}})' cannot be defined in '__builtin_offsetof'}}
-  { 
-    int a;
-    int b;
-  }, a);
-}
-
-int struct_in_second_param() {
-  struct A {
-    int a, b;
-    int x[20];
-  };
-  return __builtin_offsetof(struct A, x[sizeof(struct B{int a;})]); // no-error
-}
-
-
-#define offsetof(TYPE, MEMBER) __builtin_offsetof(TYPE, MEMBER)
-
-
-int macro(void) {
-  return offsetof(struct A // expected-error{{'struct A' cannot be defined in 'offsetof'}}
-                           // expected-error@-1{{'struct B' cannot be defined in 'offsetof'}}
-  { 
-    int a;
-    struct B // verifier seems to think the error is emitted by the macro
-             // In fact the location of the error is "B" on the line above
-    {
-      int c;
-      int d;
-    } x;
-  }, a);
-}
-
-#undef offsetof
-
-#define offsetof(TYPE, MEMBER) (&((TYPE *)0)->MEMBER)
-
-// no warning for traditional offsetof as a function-like macro
-int * macro_func(void) {
-  return offsetof(struct A // no-warning
-  { 
-    int a;
-    int b;
-  }, a);
-}
diff --git a/clang/test/C/drs/dr4xx.c b/clang/test/C/drs/dr4xx.c
index f5ad1b82bec4..768897cd4f2b 100644
--- a/clang/test/C/drs/dr4xx.c
+++ b/clang/test/C/drs/dr4xx.c
@@ -352,10 +352,11 @@ void dr496(void) {
                                              */
 
   /* The DR asked a question about whether defining a new type within offsetof
-   * is allowed. C2x N2350 made this explicitly undefined behavior, but GCC
-   * supports it, Clang diagnoses this a UB and rejects it.
+   * is allowed. C2x N2350 made this explicitly undefined behavior, but Clang
+   * has always supported defining a type in this location, and GCC also
+   * supports it.
    */
-   (void)__builtin_offsetof(struct S { int a; }, a); /* expected-error{{'struct S' cannot be defined in '__builtin_offsetof'}} */
+   (void)__builtin_offsetof(struct S { int a; }, a);
 }
 
 /* WG14 DR499: yes
diff --git a/clang/test/Parser/declarators.c b/clang/test/Parser/declarators.c
index 3af09817e6b6..464fafeaa0d2 100644
--- a/clang/test/Parser/declarators.c
+++ b/clang/test/Parser/declarators.c
@@ -80,6 +80,10 @@ struct test9 {
 struct test10 { int a; } static test10x;
 struct test11 { int a; } const test11x;
 
+// PR6216
+void test12(void) {
+  (void)__builtin_offsetof(struct { char c; int i; }, i);
+}
 
 // rdar://7608537
 struct test13 { int a; } (test13x);
diff --git a/clang/test/SemaCXX/offsetof.cpp b/clang/test/SemaCXX/offsetof.cpp
index 3eee6fb41d33..c4b288aa05d4 100644
--- a/clang/test/SemaCXX/offsetof.cpp
+++ b/clang/test/SemaCXX/offsetof.cpp
@@ -83,20 +83,3 @@ struct Derived : virtual Base {
                                                               expected-error {{invalid application of 'offsetof' to a field of a virtual base}}
 };
 }
-
-// Reject definitions in __builtin_offsetof
-// https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2350.htm
-int test_definition(void) {
-  return __builtin_offsetof(struct A // expected-error{{'A' cannot be defined in '__builtin_offsetof'}} 
-  { 
-    int a;
-    struct B // FIXME: error diagnostic message for nested definitions 
-             // https://reviews.llvm.org/D133574 
-             // fixme-error{{'A' cannot be defined in '__builtin_offsetof'}} 
-    {
-      int c;
-      int d;
-    };
-    B x;
-  }, a);
-}
-- 
2.30.2