P0217R3: Parsing support and framework for AST representation of C++1z

decomposition declarations.

There are a couple of things in the wording that seem strange here:
decomposition declarations are permitted at namespace scope (which we partially
support here) and they are permitted as the declaration in a template (which we
reject).


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@276492 91177308-0d34-0410-b5e6-96231b3b80d8

4 files changed, 65 insertions, 2 deletions

diff --git a/lib/AST/ASTDumper.cpp b/lib/AST/ASTDumper.cpp
index 872ba356a9..1a4207f512 100644
--- a/lib/AST/ASTDumper.cpp
+++ b/lib/AST/ASTDumper.cpp
@@ -428,6 +428,7 @@ namespace  {
     void VisitFunctionDecl(const FunctionDecl *D);
     void VisitFieldDecl(const FieldDecl *D);
     void VisitVarDecl(const VarDecl *D);
+    void VisitDecompositionDecl(const DecompositionDecl *D);
     void VisitFileScopeAsmDecl(const FileScopeAsmDecl *D);
     void VisitImportDecl(const ImportDecl *D);
     void VisitPragmaCommentDecl(const PragmaCommentDecl *D);
@@ -1217,6 +1218,12 @@ void ASTDumper::VisitVarDecl(const VarDecl *D) {
   }
 }
 
+void ASTDumper::VisitDecompositionDecl(const DecompositionDecl *D) {
+  VisitVarDecl(D);
+  for (auto *B : D->bindings())
+    dumpDecl(B);
+}
+
 void ASTDumper::VisitFileScopeAsmDecl(const FileScopeAsmDecl *D) {
   dumpStmt(D->getAsmString());
 }
diff --git a/lib/AST/DeclBase.cpp b/lib/AST/DeclBase.cpp
index e07bf480ec..8918e18d43 100644
--- a/lib/AST/DeclBase.cpp
+++ b/lib/AST/DeclBase.cpp
@@ -598,6 +598,7 @@ unsigned Decl::getIdentifierNamespaceForKind(Kind DeclKind) {
     case CXXConversion:
     case EnumConstant:
     case Var:
+    case Binding:
     case ImplicitParam:
     case ParmVar:
     case ObjCMethod:
@@ -678,6 +679,7 @@ unsigned Decl::getIdentifierNamespaceForKind(Kind DeclKind) {
     case Captured:
     case TranslationUnit:
     case ExternCContext:
+    case Decomposition:
 
     case UsingDirective:
     case BuiltinTemplate:
diff --git a/lib/AST/DeclCXX.cpp b/lib/AST/DeclCXX.cpp
index d069bfdc3d..7e6c725348 100644
--- a/lib/AST/DeclCXX.cpp
+++ b/lib/AST/DeclCXX.cpp
@@ -2306,6 +2306,44 @@ StaticAssertDecl *StaticAssertDecl::CreateDeserialized(ASTContext &C,
                                       nullptr, SourceLocation(), false);
 }
 
+void BindingDecl::anchor() {}
+
+BindingDecl *BindingDecl::Create(ASTContext &C, DeclContext *DC,
+                                 SourceLocation IdLoc, IdentifierInfo *Id) {
+  return new (C, DC) BindingDecl(DC, IdLoc, Id);
+}
+
+BindingDecl *BindingDecl::CreateDeserialized(ASTContext &C, unsigned ID) {
+  return new (C, ID) BindingDecl(nullptr, SourceLocation(), nullptr);
+}
+
+void DecompositionDecl::anchor() {}
+
+DecompositionDecl *DecompositionDecl::Create(ASTContext &C, DeclContext *DC,
+                                             SourceLocation StartLoc,
+                                             SourceLocation LSquareLoc,
+                                             QualType T, TypeSourceInfo *TInfo,
+                                             StorageClass SC,
+                                             ArrayRef<BindingDecl *> Bindings) {
+  size_t Extra = additionalSizeToAlloc<BindingDecl *>(Bindings.size());
+  return new (C, DC, Extra)
+      DecompositionDecl(C, DC, StartLoc, LSquareLoc, T, TInfo, SC, Bindings);
+}
+
+DecompositionDecl *DecompositionDecl::CreateDeserialized(ASTContext &C,
+                                                         unsigned ID,
+                                                         unsigned NumBindings) {
+  size_t Extra = additionalSizeToAlloc<BindingDecl *>(NumBindings);
+  auto *Result = new (C, ID, Extra) DecompositionDecl(
+      C, nullptr, SourceLocation(), SourceLocation(), QualType(), nullptr, StorageClass(), None);
+  // Set up and clean out the bindings array.
+  Result->NumBindings = NumBindings;
+  auto *Trail = Result->getTrailingObjects<BindingDecl *>();
+  for (unsigned I = 0; I != NumBindings; ++I)
+    new (Trail + I) BindingDecl*(nullptr);
+  return Result;
+}
+
 MSPropertyDecl *MSPropertyDecl::Create(ASTContext &C, DeclContext *DC,
                                        SourceLocation L, DeclarationName N,
                                        QualType T, TypeSourceInfo *TInfo,
diff --git a/lib/AST/ItaniumMangle.cpp b/lib/AST/ItaniumMangle.cpp
index 51de561d5f..5b278314ae 100644
--- a/lib/AST/ItaniumMangle.cpp
+++ b/lib/AST/ItaniumMangle.cpp
@@ -593,7 +593,7 @@ bool ItaniumMangleContextImpl::shouldMangleCXXName(const NamedDecl *D) {
     return false;
 
   const VarDecl *VD = dyn_cast<VarDecl>(D);
-  if (VD) {
+  if (VD && !isa<DecompositionDecl>(D)) {
     // C variables are not mangled.
     if (VD->isExternC())
       return false;
@@ -1193,7 +1193,23 @@ void CXXNameMangler::mangleUnqualifiedName(const NamedDecl *ND,
   //                     ::= <source-name>
   switch (Name.getNameKind()) {
   case DeclarationName::Identifier: {
-    if (const IdentifierInfo *II = Name.getAsIdentifierInfo()) {
+    const IdentifierInfo *II = Name.getAsIdentifierInfo();
+
+    // We mangle decomposition declarations as the name of their first binding.
+    if (auto *DD = dyn_cast<DecompositionDecl>(ND)) {
+      auto B = DD->bindings();
+      if (B.begin() == B.end()) {
+        // FIXME: This is ill-formed but we accept it as an extension.
+        DiagnosticsEngine &Diags = Context.getDiags();
+        unsigned DiagID = Diags.getCustomDiagID(DiagnosticsEngine::Error,
+            "cannot mangle global empty decomposition decl");
+        Diags.Report(DD->getLocation(), DiagID);
+        break;
+      }
+      II = (*B.begin())->getIdentifier();
+    }
+
+    if (II) {
       // We must avoid conflicts between internally- and externally-
       // linked variable and function declaration names in the same TU:
       //   void test() { extern void foo(); }