Include RecordDecls from anonymous unions in the AST.

For

  void f() {
    union { int i; };
  }

clang used to omit the RecordDecl from the anonymous union from the AST.
That's because the code creating it only called PushOnScopeChains(), which adds
it to the current DeclContext, which here is the function's DeclContext. But
RecursiveASTVisitor doesn't descent into all decls in a FunctionDecl.

Instead, for DeclContexts that contain statements, return the RecordDecl so
that it can be included in the DeclStmt containing the VarDecl for the union.

Interesting bits from the AST before this change:

|-FunctionDecl
| `-CompoundStmt
|   |-DeclStmt
|   | `-VarDecl 0x589cd60 <col:3> col:3 implicit used 'union (anonymous at test.cc:3:3)' callinit

After this change:

-FunctionDecl
| `-CompoundStmt
|   |-DeclStmt
|   | |-CXXRecordDecl 0x4612e48 <col:3, col:18> col:3 union definition
|   | | |-FieldDecl 0x4612f70 <col:11, col:15> col:15 referenced i 'int'
|   | `-VarDecl 0x4613010 <col:3> col:3 implicit used 'union (anonymous at test.cc:3:3)' callinit

This is now closer to how anonymous struct and unions are represented as
members of structs.  It also enabled deleting some one-off code in the
template instantiation code.

Finally, it fixes a crash with ASTMatchers, see the included test case
(this fixes http://crbug.com/580749).



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@259079 91177308-0d34-0410-b5e6-96231b3b80d8

Author: nico

include/clang/Sema/Sema.h

@@ -1861,12 +1861,12 @@ class Sema {
   void ActOnPopScope(SourceLocation Loc, Scope *S);
   void ActOnTranslationUnitScope(Scope *S);
 
-  Decl *ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS,
-                                   DeclSpec &DS);
-  Decl *ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS,
-                                   DeclSpec &DS,
+  Decl *ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
+                                   RecordDecl *&AnonRecord);
+  Decl *ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
                                    MultiTemplateParamsArg TemplateParams,
-                                   bool IsExplicitInstantiation = false);
+                                   bool IsExplicitInstantiation,
+                                   RecordDecl *&AnonRecord);
 
   Decl *BuildAnonymousStructOrUnion(Scope *S, DeclSpec &DS,
                                     AccessSpecifier AS,

lib/Parse/ParseDecl.cpp

@@ -1530,9 +1530,14 @@ Parser::ParseSimpleDeclaration(unsigned Context,
     ProhibitAttributes(Attrs);
     DeclEnd = Tok.getLocation();
     if (RequireSemi) ConsumeToken();
+    RecordDecl *AnonRecord = nullptr;
     Decl *TheDecl = Actions.ParsedFreeStandingDeclSpec(getCurScope(), AS_none,
-                                                       DS);
+                                                       DS, AnonRecord);
     DS.complete(TheDecl);
+    if (AnonRecord) {
+      Decl* decls[] = {AnonRecord, TheDecl};
+      return Actions.BuildDeclaratorGroup(decls, /*TypeMayContainAuto=*/false);
+    }
     return Actions.ConvertDeclToDeclGroup(TheDecl);
   }
 
@@ -3520,8 +3525,10 @@ void Parser::ParseStructDeclaration(
   // If there are no declarators, this is a free-standing declaration
   // specifier. Let the actions module cope with it.
   if (Tok.is(tok::semi)) {
+    RecordDecl *AnonRecord = nullptr;
     Decl *TheDecl = Actions.ParsedFreeStandingDeclSpec(getCurScope(), AS_none,
-                                                       DS);
+                                                       DS, AnonRecord);
+    assert(!AnonRecord && "Did not expect anonymous struct or union here");
     DS.complete(TheDecl);
     return;
   }

lib/Parse/ParseDeclCXX.cpp

@@ -2400,10 +2400,15 @@ Parser::ParseCXXClassMemberDeclaration(AccessSpecifier AS,
     if (DS.isFriendSpecified())
       ProhibitAttributes(FnAttrs);
 
-    Decl *TheDecl =
-      Actions.ParsedFreeStandingDeclSpec(getCurScope(), AS, DS, TemplateParams);
+    RecordDecl *AnonRecord = nullptr;
+    Decl *TheDecl = Actions.ParsedFreeStandingDeclSpec(
+        getCurScope(), AS, DS, TemplateParams, false, AnonRecord);
     DS.complete(TheDecl);
-    return DeclGroupPtrTy::make(DeclGroupRef(TheDecl));
+    if (AnonRecord) {
+      Decl* decls[] = {AnonRecord, TheDecl};
+      return Actions.BuildDeclaratorGroup(decls, /*TypeMayContainAuto=*/false);
+    }
+    return Actions.ConvertDeclToDeclGroup(TheDecl);
   }
 
   ParsingDeclarator DeclaratorInfo(*this, DS, Declarator::MemberContext);

lib/Parse/ParseTemplate.cpp

@@ -209,11 +209,15 @@ Parser::ParseSingleDeclarationAfterTemplate(
   if (Tok.is(tok::semi)) {
     ProhibitAttributes(prefixAttrs);
     DeclEnd = ConsumeToken();
+    RecordDecl *AnonRecord = nullptr;
     Decl *Decl = Actions.ParsedFreeStandingDeclSpec(
         getCurScope(), AS, DS,
         TemplateInfo.TemplateParams ? *TemplateInfo.TemplateParams
                                     : MultiTemplateParamsArg(),
-        TemplateInfo.Kind == ParsedTemplateInfo::ExplicitInstantiation);
+        TemplateInfo.Kind == ParsedTemplateInfo::ExplicitInstantiation,
+        AnonRecord);
+    assert(!AnonRecord &&
+           "Anonymous unions/structs should not be valid with template");
     DS.complete(Decl);
     return Decl;
   }

lib/Parse/Parser.cpp

@@ -883,8 +883,14 @@ Parser::ParseDeclOrFunctionDefInternal(ParsedAttributesWithRange &attrs,
   if (Tok.is(tok::semi)) {
     ProhibitAttributes(attrs);
     ConsumeToken();
-    Decl *TheDecl = Actions.ParsedFreeStandingDeclSpec(getCurScope(), AS, DS);
+    RecordDecl *AnonRecord = nullptr;
+    Decl *TheDecl = Actions.ParsedFreeStandingDeclSpec(getCurScope(), AS_none,
+                                                       DS, AnonRecord);
     DS.complete(TheDecl);
+    if (AnonRecord) {
+      Decl* decls[] = {AnonRecord, TheDecl};
+      return Actions.BuildDeclaratorGroup(decls, /*TypeMayContainAuto=*/false);
+    }
     return Actions.ConvertDeclToDeclGroup(TheDecl);
   }
 

lib/Sema/SemaDecl.cpp

@@ -3601,9 +3601,11 @@ void Sema::MergeVarDecl(VarDecl *New, LookupResult &Previous) {
 
 /// ParsedFreeStandingDeclSpec - This method is invoked when a declspec with
 /// no declarator (e.g. "struct foo;") is parsed.
-Decl *Sema::ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS,
-                                       DeclSpec &DS) {
-  return ParsedFreeStandingDeclSpec(S, AS, DS, MultiTemplateParamsArg());
+Decl *
+Sema::ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
+                                 RecordDecl *&AnonRecord) {
+  return ParsedFreeStandingDeclSpec(S, AS, DS, MultiTemplateParamsArg(), false,
+                                    AnonRecord);
 }
 
 // The MS ABI changed between VS2013 and VS2015 with regard to numbers used to
@@ -3709,10 +3711,11 @@ static unsigned GetDiagnosticTypeSpecifierID(DeclSpec::TST T) {
 /// ParsedFreeStandingDeclSpec - This method is invoked when a declspec with
 /// no declarator (e.g. "struct foo;") is parsed. It also accepts template
 /// parameters to cope with template friend declarations.
-Decl *Sema::ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS,
-                                       DeclSpec &DS,
-                                       MultiTemplateParamsArg TemplateParams,
-                                       bool IsExplicitInstantiation) {
+Decl *
+Sema::ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS, DeclSpec &DS,
+                                 MultiTemplateParamsArg TemplateParams,
+                                 bool IsExplicitInstantiation,
+                                 RecordDecl *&AnonRecord) {
   Decl *TagD = nullptr;
   TagDecl *Tag = nullptr;
   if (DS.getTypeSpecType() == DeclSpec::TST_class ||
@@ -3807,9 +3810,19 @@ Decl *Sema::ParsedFreeStandingDeclSpec(Scope *S, AccessSpecifier AS,
     if (!Record->getDeclName() && Record->isCompleteDefinition() &&
         DS.getStorageClassSpec() != DeclSpec::SCS_typedef) {
       if (getLangOpts().CPlusPlus ||
-          Record->getDeclContext()->isRecord())
+          Record->getDeclContext()->isRecord()) {
+        // If CurContext is a DeclContext that can contain statements,
+        // RecursiveASTVisitor won't visit the decls that
+        // BuildAnonymousStructOrUnion() will put into CurContext.
+        // Also store them here so that they can be part of the
+        // DeclStmt that gets created in this case.
+        // FIXME: Also return the IndirectFieldDecls created by
+        // BuildAnonymousStructOr union, for the same reason?
+        if (CurContext->isFunctionOrMethod())
+          AnonRecord = Record;
         return BuildAnonymousStructOrUnion(S, DS, AS, Record,
                                            Context.getPrintingPolicy());
+      }
 
       DeclaresAnything = false;
     }

lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -491,13 +491,6 @@ Decl *TemplateDeclInstantiator::VisitVarDecl(VarDecl *D) {
 Decl *TemplateDeclInstantiator::VisitVarDecl(VarDecl *D,
                                              bool InstantiatingVarTemplate) {
 
-  // If this is the variable for an anonymous struct or union,
-  // instantiate the anonymous struct/union type first.
-  if (const RecordType *RecordTy = D->getType()->getAs<RecordType>())
-    if (RecordTy->getDecl()->isAnonymousStructOrUnion())
-      if (!VisitCXXRecordDecl(cast<CXXRecordDecl>(RecordTy->getDecl())))
-        return nullptr;
-
   // Do substitution on the type of the declaration
   TypeSourceInfo *DI = SemaRef.SubstType(D->getTypeSourceInfo(),
                                          TemplateArgs,
@@ -2673,13 +2666,6 @@ Decl *TemplateDeclInstantiator::VisitVarTemplateSpecializationDecl(
     const TemplateArgumentListInfo &TemplateArgsInfo,
     ArrayRef<TemplateArgument> Converted) {
 
-  // If this is the variable for an anonymous struct or union,
-  // instantiate the anonymous struct/union type first.
-  if (const RecordType *RecordTy = D->getType()->getAs<RecordType>())
-    if (RecordTy->getDecl()->isAnonymousStructOrUnion())
-      if (!VisitCXXRecordDecl(cast<CXXRecordDecl>(RecordTy->getDecl())))
-        return nullptr;
-
   // Do substitution on the type of the declaration
   TypeSourceInfo *DI =
       SemaRef.SubstType(D->getTypeSourceInfo(), TemplateArgs,

unittests/ASTMatchers/ASTMatchersTest.cpp

@@ -4240,6 +4240,28 @@ TEST(HasAncestor, ImplicitArrayCopyCtorDeclRefExpr) {
                       declRefExpr(to(decl(hasAncestor(decl()))))));
 }
 
+TEST(HasAncestor, AnonymousUnionMemberExpr) {
+  EXPECT_TRUE(matches("int F() {\n"
+                      "  union { int i; };\n"
+                      "  return i;\n"
+                      "}\n",
+                      memberExpr(member(hasAncestor(decl())))));
+  EXPECT_TRUE(matches("void f() {\n"
+                      "  struct {\n"
+                      "    struct { int a; int b; };\n"
+                      "  } s;\n"
+                      "  s.a = 4;\n"
+                      "}\n",
+                      memberExpr(member(hasAncestor(decl())))));
+  EXPECT_TRUE(matches("void f() {\n"
+                      "  struct {\n"
+                      "    struct { int a; int b; };\n"
+                      "  } s;\n"
+                      "  s.a = 4;\n"
+                      "}\n",
+                      declRefExpr(to(decl(hasAncestor(decl()))))));
+}
+
 TEST(HasParent, MatchesAllParents) {
   EXPECT_TRUE(matches(
       "template <typename T> struct C { static void f() { 42; } };"