[Clang] Fix memory leak due to TemplateArgumentListInfo used in AST node.

It looks like the leak is rooted at the allocation here:
1a155ee7de/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp (L3857)

The VarTemplateSpecializationDecl is allocated using placement new which uses the AST structure for ownership: 1a155ee7de/clang/lib/AST/DeclBase.cpp (L99)

The problem is the TemplateArgumentListInfo inside 1a155ee7de/clang/include/clang/AST/DeclTemplate.h (L2721)
This object contains a vector which does not use placement new: 1a155ee7de/clang/include/clang/AST/TemplateBase.h (L564)

Apparently ASTTemplateArgumentListInfo should be used instead 1a155ee7de/clang/include/clang/AST/TemplateBase.h (L575)

https://reviews.llvm.org/D125802#3551305

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D126944

clang-tools-extra/clangd/AST.cpp

@@ -53,8 +53,10 @@ getTemplateSpecializationArgLocs(const NamedDecl &ND) {
                  llvm::dyn_cast<VarTemplatePartialSpecializationDecl>(&ND)) {
     if (auto *Args = Var->getTemplateArgsAsWritten())
       return Args->arguments();
-  } else if (auto *Var = llvm::dyn_cast<VarTemplateSpecializationDecl>(&ND))
-    return Var->getTemplateArgsInfo().arguments();
+  } else if (auto *Var = llvm::dyn_cast<VarTemplateSpecializationDecl>(&ND)) {
+    if (auto *Args = Var->getTemplateArgsInfo())
+      return Args->arguments();
+  }
   // We return None for ClassTemplateSpecializationDecls because it does not
   // contain TemplateArgumentLoc information.
   return llvm::None;

clang/docs/ReleaseNotes.rst

@@ -168,6 +168,8 @@ Bug Fixes
   `Issue 55562 <https://github.com/llvm/llvm-project/issues/55562>`_.
 - Clang will allow calling a ``consteval`` function in a default argument. This
   fixes `Issue 48230 <https://github.com/llvm/llvm-project/issues/48230>`_.
+- Fixed memory leak due to ``VarTemplateSpecializationDecl`` using
+  ``TemplateArgumentListInfo`` instead of ``ASTTemplateArgumentListInfo``.
 
 Improvements to Clang's diagnostics
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

clang/include/clang/AST/DeclTemplate.h

@@ -2718,7 +2718,7 @@ class VarTemplateSpecializationDecl : public VarDecl,
 
   /// The template arguments used to describe this specialization.
   const TemplateArgumentList *TemplateArgs;
-  TemplateArgumentListInfo TemplateArgsInfo;
+  const ASTTemplateArgumentListInfo *TemplateArgsInfo = nullptr;
 
   /// The point where this template was instantiated (if any).
   SourceLocation PointOfInstantiation;
@@ -2773,8 +2773,9 @@ public:
 
   // TODO: Always set this when creating the new specialization?
   void setTemplateArgsInfo(const TemplateArgumentListInfo &ArgsInfo);
+  void setTemplateArgsInfo(const ASTTemplateArgumentListInfo *ArgsInfo);
 
-  const TemplateArgumentListInfo &getTemplateArgsInfo() const {
+  const ASTTemplateArgumentListInfo *getTemplateArgsInfo() const {
     return TemplateArgsInfo;
   }
 

clang/include/clang/AST/TemplateBase.h

@@ -618,6 +618,9 @@ private:
 
   ASTTemplateArgumentListInfo(const TemplateArgumentListInfo &List);
 
+  // FIXME: Is it ever necessary to copy to another context?
+  ASTTemplateArgumentListInfo(const ASTTemplateArgumentListInfo *List);
+
 public:
   /// The source location of the left angle bracket ('<').
   SourceLocation LAngleLoc;
@@ -647,6 +650,10 @@ public:
 
   static const ASTTemplateArgumentListInfo *
   Create(const ASTContext &C, const TemplateArgumentListInfo &List);
+
+  // FIXME: Is it ever necessary to copy to another context?
+  static const ASTTemplateArgumentListInfo *
+  Create(const ASTContext &C, const ASTTemplateArgumentListInfo *List);
 };
 
 /// Represents an explicit template argument list in C++, e.g.,

clang/lib/AST/ASTImporter.cpp

@@ -6018,9 +6018,10 @@ ExpectedDecl ASTNodeImporter::VisitVarTemplateSpecializationDecl(
       return TInfoOrErr.takeError();
 
     TemplateArgumentListInfo ToTAInfo;
-    if (Error Err = ImportTemplateArgumentListInfo(
-        D->getTemplateArgsInfo(), ToTAInfo))
+    if (const ASTTemplateArgumentListInfo *Args = D->getTemplateArgsInfo()) {
+      if (Error Err = ImportTemplateArgumentListInfo(*Args, ToTAInfo))
         return std::move(Err);
+    }
 
     using PartVarSpecDecl = VarTemplatePartialSpecializationDecl;
     // Create a new specialization.

clang/lib/AST/DeclTemplate.cpp

@@ -1335,10 +1335,14 @@ VarTemplateDecl *VarTemplateSpecializationDecl::getSpecializedTemplate() const {
 
 void VarTemplateSpecializationDecl::setTemplateArgsInfo(
     const TemplateArgumentListInfo &ArgsInfo) {
-  TemplateArgsInfo.setLAngleLoc(ArgsInfo.getLAngleLoc());
-  TemplateArgsInfo.setRAngleLoc(ArgsInfo.getRAngleLoc());
-  for (const TemplateArgumentLoc &Loc : ArgsInfo.arguments())
-    TemplateArgsInfo.addArgument(Loc);
+  TemplateArgsInfo =
+      ASTTemplateArgumentListInfo::Create(getASTContext(), ArgsInfo);
+}
+
+void VarTemplateSpecializationDecl::setTemplateArgsInfo(
+    const ASTTemplateArgumentListInfo *ArgsInfo) {
+  TemplateArgsInfo =
+      ASTTemplateArgumentListInfo::Create(getASTContext(), ArgsInfo);
 }
 
 //===----------------------------------------------------------------------===//

clang/lib/AST/TemplateBase.cpp

@@ -617,6 +617,17 @@ ASTTemplateArgumentListInfo::Create(const ASTContext &C,
   return new (Mem) ASTTemplateArgumentListInfo(List);
 }
 
+const ASTTemplateArgumentListInfo *
+ASTTemplateArgumentListInfo::Create(const ASTContext &C,
+                                    const ASTTemplateArgumentListInfo *List) {
+  if (!List)
+    return nullptr;
+  std::size_t size =
+      totalSizeToAlloc<TemplateArgumentLoc>(List->getNumTemplateArgs());
+  void *Mem = C.Allocate(size, alignof(ASTTemplateArgumentListInfo));
+  return new (Mem) ASTTemplateArgumentListInfo(List);
+}
+
 ASTTemplateArgumentListInfo::ASTTemplateArgumentListInfo(
     const TemplateArgumentListInfo &Info) {
   LAngleLoc = Info.getLAngleLoc();
@@ -628,6 +639,17 @@ ASTTemplateArgumentListInfo::ASTTemplateArgumentListInfo(
     new (&ArgBuffer[i]) TemplateArgumentLoc(Info[i]);
 }
 
+ASTTemplateArgumentListInfo::ASTTemplateArgumentListInfo(
+    const ASTTemplateArgumentListInfo *Info) {
+  LAngleLoc = Info->getLAngleLoc();
+  RAngleLoc = Info->getRAngleLoc();
+  NumTemplateArgs = Info->getNumTemplateArgs();
+
+  TemplateArgumentLoc *ArgBuffer = getTrailingObjects<TemplateArgumentLoc>();
+  for (unsigned i = 0; i != NumTemplateArgs; ++i)
+    new (&ArgBuffer[i]) TemplateArgumentLoc((*Info)[i]);
+}
+
 void ASTTemplateKWAndArgsInfo::initializeFrom(
     SourceLocation TemplateKWLoc, const TemplateArgumentListInfo &Info,
     TemplateArgumentLoc *OutArgArray) {

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -3801,13 +3801,15 @@ Decl *TemplateDeclInstantiator::VisitVarTemplateSpecializationDecl(
     return nullptr;
 
   // Substitute the current template arguments.
-  const TemplateArgumentListInfo &TemplateArgsInfo = D->getTemplateArgsInfo();
-  VarTemplateArgsInfo.setLAngleLoc(TemplateArgsInfo.getLAngleLoc());
-  VarTemplateArgsInfo.setRAngleLoc(TemplateArgsInfo.getRAngleLoc());
+  if (const ASTTemplateArgumentListInfo *TemplateArgsInfo =
+          D->getTemplateArgsInfo()) {
+    VarTemplateArgsInfo.setLAngleLoc(TemplateArgsInfo->getLAngleLoc());
+    VarTemplateArgsInfo.setRAngleLoc(TemplateArgsInfo->getRAngleLoc());
 
-  if (SemaRef.SubstTemplateArguments(TemplateArgsInfo.arguments(), TemplateArgs,
-                                     VarTemplateArgsInfo))
+    if (SemaRef.SubstTemplateArguments(TemplateArgsInfo->arguments(),
+                                       TemplateArgs, VarTemplateArgsInfo))
       return nullptr;
+  }
 
   // Check that the template argument list is well-formed for this template.
   SmallVector<TemplateArgument, 4> Converted;
@@ -5554,8 +5556,18 @@ void Sema::InstantiateVariableDefinition(SourceLocation PointOfInstantiation,
     // declaration of the definition.
     TemplateDeclInstantiator Instantiator(*this, Var->getDeclContext(),
                                           TemplateArgs);
+
+    TemplateArgumentListInfo TemplateArgInfo;
+    if (const ASTTemplateArgumentListInfo *ArgInfo =
+            VarSpec->getTemplateArgsInfo()) {
+      TemplateArgInfo.setLAngleLoc(ArgInfo->getLAngleLoc());
+      TemplateArgInfo.setRAngleLoc(ArgInfo->getRAngleLoc());
+      for (const TemplateArgumentLoc &Arg : ArgInfo->arguments())
+        TemplateArgInfo.addArgument(Arg);
+    }
+
     Var = cast_or_null<VarDecl>(Instantiator.VisitVarTemplateSpecializationDecl(
-        VarSpec->getSpecializedTemplate(), Def, VarSpec->getTemplateArgsInfo(),
+        VarSpec->getSpecializedTemplate(), Def, TemplateArgInfo,
         VarSpec->getTemplateArgs().asArray(), VarSpec));
     if (Var) {
       llvm::PointerUnion<VarTemplateDecl *,