[Clang][P1061] Fix crash

Author: ricejasonf

clang/include/clang/AST/DeclCXX.h

@@ -4199,8 +4199,16 @@ class DecompositionDecl final
         NumBindings(Bindings.size()) {
     std::uninitialized_copy(Bindings.begin(), Bindings.end(),
                             getTrailingObjects<BindingDecl *>());
-    for (auto *B : Bindings)
+    for (auto *B : Bindings) {
       B->setDecomposedDecl(this);
+      if (B->isParameterPack()) {
+        for (Expr *E : B->getBindingPackExprs()) {
+          auto *DRE = cast<DeclRefExpr>(E);
+          auto *NestedB = cast<BindingDecl>(DRE->getDecl());
+          NestedB->setDecomposedDecl(this);
+        }
+      }
+    }
   }
 
   void anchor() override;

clang/lib/AST/DeclCXX.cpp

@@ -3426,6 +3426,8 @@ VarDecl *BindingDecl::getHoldingVar() const {
 }
 
 llvm::ArrayRef<Expr *> BindingDecl::getBindingPackExprs() const {
+  if (!Binding)
+    return {};
   auto *RP = cast<ResolvedUnexpandedPackExpr>(Binding);
   return RP->getExprs();
 }

clang/lib/AST/ExprCXX.cpp

@@ -1996,7 +1996,7 @@ ResolvedUnexpandedPackExpr::Create(ASTContext &Ctx, SourceLocation BL,
       new (Mem) ResolvedUnexpandedPackExpr(BL, T, NumExprs);
 
   auto Exprs = New->getExprs();
-  std::fill(Exprs.begin(), Exprs.end(), nullptr);
+  std::uninitialized_fill(Exprs.begin(), Exprs.end(), nullptr);
 
   return New;
 }
@@ -2005,7 +2005,7 @@ ResolvedUnexpandedPackExpr *
 ResolvedUnexpandedPackExpr::Create(ASTContext &Ctx, SourceLocation BL,
                                    QualType T, ArrayRef<Expr *> Exprs) {
   auto *New = Create(Ctx, BL, T, Exprs.size());
-  std::copy(Exprs.begin(), Exprs.end(), New->getExprs().begin());
+  std::uninitialized_copy(Exprs.begin(), Exprs.end(), New->getExprs().begin());
   return New;
 }
 

clang/lib/Sema/SemaDeclCXX.cpp

@@ -981,20 +981,14 @@ static bool CheckBindingsCount(Sema &S, DecompositionDecl *DD,
   }
 
   if (IsValid && HasPack) {
-    TemplateTypeParmDecl *DummyTemplateParam = TemplateTypeParmDecl::Create(
-        S.Context, S.Context.getTranslationUnitDecl(),
-        /*KeyLoc*/ SourceLocation(), /*NameLoc*/ SourceLocation(),
-        /*TemplateDepth*/ 0, /*AutoParameterPosition*/ 0,
-        /*Identifier*/ nullptr, false, /*IsParameterPack*/ true);
-
     // create the pack expr and assign it to the binding
     unsigned PackSize = MemberCount - Bindings.size() + 1;
     QualType PackType = S.Context.getPackExpansionType(
-        QualType(DummyTemplateParam->getTypeForDecl(), 0), PackSize);
-    (*BindingWithPackItr)
-        ->setBinding(PackType,
-                     ResolvedUnexpandedPackExpr::Create(
-                         S.Context, DD->getBeginLoc(), DecompType, PackSize));
+        S.Context.DependentTy, std::nullopt, /*ExpectsPackInType=*/false);
+    BindingDecl *BD = (*BindingWithPackItr);
+    BD->setBinding(PackType,
+                   ResolvedUnexpandedPackExpr::Create(
+                       S.Context, DD->getBeginLoc(), DecompType, PackSize));
   }
 
   if (IsValid)