[c++20] Implement P0428R2 - Familiar template syntax for generic lambdas

Differential Revision: https://reviews.llvm.org/D36527

llvm-svn: 359967

10 files changed, 182 insertions, 41 deletions

diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
index 9946d16a858..b9ecdc65720 100644
--- a/clang/lib/AST/DeclCXX.cpp
+++ b/clang/lib/AST/DeclCXX.cpp
@@ -1421,13 +1421,30 @@ void CXXRecordDecl::getCaptureFields(
 
 TemplateParameterList *
 CXXRecordDecl::getGenericLambdaTemplateParameterList() const {
-  if (!isLambda()) return nullptr;
+  if (!isGenericLambda()) return nullptr;
   CXXMethodDecl *CallOp = getLambdaCallOperator();
   if (FunctionTemplateDecl *Tmpl = CallOp->getDescribedFunctionTemplate())
     return Tmpl->getTemplateParameters();
   return nullptr;
 }
 
+ArrayRef<NamedDecl *>
+CXXRecordDecl::getLambdaExplicitTemplateParameters() const {
+  TemplateParameterList *List = getGenericLambdaTemplateParameterList();
+  if (!List)
+    return {};
+
+  assert(std::is_partitioned(List->begin(), List->end(),
+                             [](const NamedDecl *D) { return !D->isImplicit(); })
+         && "Explicit template params should be ordered before implicit ones");
+
+  const auto ExplicitEnd = std::lower_bound(List->begin(), List->end(), false,
+                                            [](const NamedDecl *D, bool) {
+    return !D->isImplicit();
+  });
+  return llvm::makeArrayRef(List->begin(), ExplicitEnd);
+}
+
 Decl *CXXRecordDecl::getLambdaContextDecl() const {
   assert(isLambda() && "Not a lambda closure type!");
   ExternalASTSource *Source = getParentASTContext().getExternalSource();
diff --git a/clang/lib/AST/DeclPrinter.cpp b/clang/lib/AST/DeclPrinter.cpp
index 36c5d10f718..78a7afdbf09 100644
--- a/clang/lib/AST/DeclPrinter.cpp
+++ b/clang/lib/AST/DeclPrinter.cpp
@@ -15,6 +15,7 @@
 #include "clang/AST/Decl.h"
 #include "clang/AST/DeclCXX.h"
 #include "clang/AST/DeclObjC.h"
+#include "clang/AST/DeclTemplate.h"
 #include "clang/AST/DeclVisitor.h"
 #include "clang/AST/Expr.h"
 #include "clang/AST/ExprCXX.h"
@@ -105,7 +106,8 @@ namespace {
     void VisitOMPDeclareMapperDecl(OMPDeclareMapperDecl *D);
     void VisitOMPCapturedExprDecl(OMPCapturedExprDecl *D);
 
-    void printTemplateParameters(const TemplateParameterList *Params);
+    void printTemplateParameters(const TemplateParameterList *Params,
+                                 bool OmitTemplateKW = false);
     void printTemplateArguments(const TemplateArgumentList &Args,
                                 const TemplateParameterList *Params = nullptr);
     void prettyPrintAttributes(Decl *D);
@@ -126,6 +128,18 @@ void Decl::print(raw_ostream &Out, const PrintingPolicy &Policy,
   Printer.Visit(const_cast<Decl*>(this));
 }
 
+void TemplateParameterList::print(raw_ostream &Out, const ASTContext &Context,
+                                  bool OmitTemplateKW) const {
+  print(Out, Context, Context.getPrintingPolicy(), OmitTemplateKW);
+}
+
+void TemplateParameterList::print(raw_ostream &Out, const ASTContext &Context,
+                                  const PrintingPolicy &Policy,
+                                  bool OmitTemplateKW) const {
+  DeclPrinter Printer(Out, Policy, Context);
+  Printer.printTemplateParameters(this, OmitTemplateKW);
+}
+
 static QualType GetBaseType(QualType T) {
   // FIXME: This should be on the Type class!
   QualType BaseType = T;
@@ -1002,25 +1016,35 @@ void DeclPrinter::VisitLinkageSpecDecl(LinkageSpecDecl *D) {
     Visit(*D->decls_begin());
 }
 
-void DeclPrinter::printTemplateParameters(const TemplateParameterList *Params) {
+void DeclPrinter::printTemplateParameters(const TemplateParameterList *Params,
+                                          bool OmitTemplateKW) {
   assert(Params);
 
-  Out << "template <";
+  if (!OmitTemplateKW)
+    Out << "template ";
+  Out << '<';
 
-  for (unsigned i = 0, e = Params->size(); i != e; ++i) {
-    if (i != 0)
+  bool NeedComma = false;
+  for (const Decl *Param : *Params) {
+    if (Param->isImplicit())
+      continue;
+
+    if (NeedComma)
       Out << ", ";
+    else
+      NeedComma = true;
 
-    const Decl *Param = Params->getParam(i);
     if (auto TTP = dyn_cast<TemplateTypeParmDecl>(Param)) {
 
       if (TTP->wasDeclaredWithTypename())
-        Out << "typename ";
+        Out << "typename";
       else
-        Out << "class ";
+        Out << "class";
 
       if (TTP->isParameterPack())
-        Out << "...";
+        Out << " ...";
+      else if (!TTP->getName().empty())
+        Out << ' ';
 
       Out << *TTP;
 
@@ -1045,7 +1069,9 @@ void DeclPrinter::printTemplateParameters(const TemplateParameterList *Params) {
     }
   }
 
-  Out << "> ";
+  Out << '>';
+  if (!OmitTemplateKW)
+    Out << ' ';
 }
 
 void DeclPrinter::printTemplateArguments(const TemplateArgumentList &Args,
diff --git a/clang/lib/AST/ExprCXX.cpp b/clang/lib/AST/ExprCXX.cpp
index 5f9d0e7623d..b1ce1674014 100644
--- a/clang/lib/AST/ExprCXX.cpp
+++ b/clang/lib/AST/ExprCXX.cpp
@@ -1204,7 +1204,11 @@ CXXMethodDecl *LambdaExpr::getCallOperator() const {
 TemplateParameterList *LambdaExpr::getTemplateParameterList() const {
   CXXRecordDecl *Record = getLambdaClass();
   return Record->getGenericLambdaTemplateParameterList();
+}
 
+ArrayRef<NamedDecl *> LambdaExpr::getExplicitTemplateParameters() const {
+  const CXXRecordDecl *Record = getLambdaClass();
+  return Record->getLambdaExplicitTemplateParameters();
 }
 
 CompoundStmt *LambdaExpr::getBody() const {
diff --git a/clang/lib/AST/ItaniumMangle.cpp b/clang/lib/AST/ItaniumMangle.cpp
index 3357756466f..1eb5460dd61 100644
--- a/clang/lib/AST/ItaniumMangle.cpp
+++ b/clang/lib/AST/ItaniumMangle.cpp
@@ -486,6 +486,7 @@ private:
                        const AbiTagList *AdditionalAbiTags);
   void mangleBlockForPrefix(const BlockDecl *Block);
   void mangleUnqualifiedBlock(const BlockDecl *Block);
+  void mangleTemplateParamDecl(const NamedDecl *Decl);
   void mangleLambda(const CXXRecordDecl *Lambda);
   void mangleNestedName(const NamedDecl *ND, const DeclContext *DC,
                         const AbiTagList *AdditionalAbiTags,
@@ -1372,7 +1373,8 @@ void CXXNameMangler::mangleUnqualifiedName(const NamedDecl *ND,
     // <unnamed-type-name> ::= <closure-type-name>
     //
     // <closure-type-name> ::= Ul <lambda-sig> E [ <nonnegative number> ] _
-    // <lambda-sig> ::= <parameter-type>+   # Parameter types or 'v' for 'void'.
+    // <lambda-sig> ::= <template-param-decl>* <parameter-type>+
+    //     # Parameter types or 'v' for 'void'.
     if (const CXXRecordDecl *Record = dyn_cast<CXXRecordDecl>(TD)) {
       if (Record->isLambda() && Record->getLambdaManglingNumber()) {
         assert(!AdditionalAbiTags &&
@@ -1678,6 +1680,24 @@ void CXXNameMangler::mangleUnqualifiedBlock(const BlockDecl *Block) {
   Out << '_';
 }
 
+// <template-param-decl>
+//   ::= Ty                              # template type parameter
+//   ::= Tn <type>                       # template non-type parameter
+//   ::= Tt <template-param-decl>* E     # template template parameter
+void CXXNameMangler::mangleTemplateParamDecl(const NamedDecl *Decl) {
+  if (isa<TemplateTypeParmDecl>(Decl)) {
+    Out << "Ty";
+  } else if (auto *Tn = dyn_cast<NonTypeTemplateParmDecl>(Decl)) {
+    Out << "Tn";
+    mangleType(Tn->getType());
+  } else if (auto *Tt = dyn_cast<TemplateTemplateParmDecl>(Decl)) {
+    Out << "Tt";
+    for (auto *Param : *Tt->getTemplateParameters())
+      mangleTemplateParamDecl(Param);
+    Out << "E";
+  }
+}
+
 void CXXNameMangler::mangleLambda(const CXXRecordDecl *Lambda) {
   // If the context of a closure type is an initializer for a class member
   // (static or nonstatic), it is encoded in a qualified name with a final
@@ -1705,6 +1725,8 @@ void CXXNameMangler::mangleLambda(const CXXRecordDecl *Lambda) {
   }
 
   Out << "Ul";
+  for (auto *D : Lambda->getLambdaExplicitTemplateParameters())
+    mangleTemplateParamDecl(D);
   const FunctionProtoType *Proto = Lambda->getLambdaTypeInfo()->getType()->
                                    getAs<FunctionProtoType>();
   mangleBareFunctionType(Proto, /*MangleReturnType=*/false,
diff --git a/clang/lib/AST/StmtPrinter.cpp b/clang/lib/AST/StmtPrinter.cpp
index acf19aaaf41..71270220382 100644
--- a/clang/lib/AST/StmtPrinter.cpp
+++ b/clang/lib/AST/StmtPrinter.cpp
@@ -1900,8 +1900,14 @@ void StmtPrinter::VisitLambdaExpr(LambdaExpr *Node) {
   }
   OS << ']';
 
+  if (!Node->getExplicitTemplateParameters().empty()) {
+    Node->getTemplateParameterList()->print(
+        OS, Node->getLambdaClass()->getASTContext(),
+        /*OmitTemplateKW*/true);
+  }
+
   if (Node->hasExplicitParameters()) {
-    OS << " (";
+    OS << '(';
     CXXMethodDecl *Method = Node->getCallOperator();
     NeedComma = false;
     for (const auto *P : Method->parameters()) {
@@ -1936,9 +1942,8 @@ void StmtPrinter::VisitLambdaExpr(LambdaExpr *Node) {
   }
 
   // Print the body.
-  CompoundStmt *Body = Node->getBody();
   OS << ' ';
-  PrintStmt(Body);
+  PrintRawCompoundStmt(Node->getBody());
 }
 
 void StmtPrinter::VisitCXXScalarValueInitExpr(CXXScalarValueInitExpr *Node) {
diff --git a/clang/lib/AST/TypePrinter.cpp b/clang/lib/AST/TypePrinter.cpp
index 82a2fa09c76..85045324974 100644
--- a/clang/lib/AST/TypePrinter.cpp
+++ b/clang/lib/AST/TypePrinter.cpp
@@ -1217,8 +1217,18 @@ void TypePrinter::printTemplateTypeParmBefore(const TemplateTypeParmType *T,
                                               raw_ostream &OS) {
   if (IdentifierInfo *Id = T->getIdentifier())
     OS << Id->getName();
-  else
-    OS << "type-parameter-" << T->getDepth() << '-' << T->getIndex();
+  else {
+    bool IsLambdaAutoParam = false;
+    if (auto D = T->getDecl()) {
+      if (auto M = dyn_cast_or_null<CXXMethodDecl>(D->getDeclContext()))
+        IsLambdaAutoParam = D->isImplicit() && M->getParent()->isLambda();
+    }
+
+    if (IsLambdaAutoParam)
+      OS << "auto";
+    else
+      OS << "type-parameter-" << T->getDepth() << '-' << T->getIndex();
+  }
   spaceBeforePlaceHolder(OS);
 }
 
diff --git a/clang/lib/Parse/ParseExprCXX.cpp b/clang/lib/Parse/ParseExprCXX.cpp
index c3094d69923..87a6b4df8f8 100644
--- a/clang/lib/Parse/ParseExprCXX.cpp
+++ b/clang/lib/Parse/ParseExprCXX.cpp
@@ -638,6 +638,8 @@ ExprResult Parser::ParseCXXIdExpression(bool isAddressOfOperand) {
 ///
 ///       lambda-expression:
 ///         lambda-introducer lambda-declarator[opt] compound-statement
+///         lambda-introducer '<' template-parameter-list '>'
+///             lambda-declarator[opt] compound-statement
 ///
 ///       lambda-introducer:
 ///         '[' lambda-capture[opt] ']'
@@ -1121,6 +1123,33 @@ ExprResult Parser::ParseLambdaExpressionAfterIntroducer(
               << A.getName()->getName();
   };
 
+  // FIXME: Consider allowing this as an extension for GCC compatibiblity.
+  const bool HasExplicitTemplateParams = Tok.is(tok::less);
+  ParseScope TemplateParamScope(this, Scope::TemplateParamScope,
+                                /*EnteredScope=*/HasExplicitTemplateParams);
+  if (HasExplicitTemplateParams) {
+    Diag(Tok, getLangOpts().CPlusPlus2a
+                  ? diag::warn_cxx17_compat_lambda_template_parameter_list
+                  : diag::ext_lambda_template_parameter_list);
+
+    SmallVector<NamedDecl*, 4> TemplateParams;
+    SourceLocation LAngleLoc, RAngleLoc;
+    if (ParseTemplateParameters(CurTemplateDepthTracker.getDepth(),
+                                TemplateParams, LAngleLoc, RAngleLoc)) {
+      Actions.ActOnLambdaError(LambdaBeginLoc, getCurScope());
+      return ExprError();
+    }
+
+    if (TemplateParams.empty()) {
+      Diag(RAngleLoc,
+           diag::err_lambda_template_parameter_list_empty);
+    } else {
+      Actions.ActOnLambdaExplicitTemplateParameterList(
+          LAngleLoc, TemplateParams, RAngleLoc);
+      ++CurTemplateDepthTracker;
+    }
+  }
+
   TypeResult TrailingReturnType;
   if (Tok.is(tok::l_paren)) {
     ParseScope PrototypeScope(this,
@@ -1137,13 +1166,20 @@ ExprResult Parser::ParseLambdaExpressionAfterIntroducer(
     SourceLocation EllipsisLoc;
 
     if (Tok.isNot(tok::r_paren)) {
-      Actions.RecordParsingTemplateParameterDepth(TemplateParameterDepth);
+      Actions.RecordParsingTemplateParameterDepth(
+          CurTemplateDepthTracker.getOriginalDepth());
+
       ParseParameterDeclarationClause(D, Attr, ParamInfo, EllipsisLoc);
+
       // For a generic lambda, each 'auto' within the parameter declaration
       // clause creates a template type parameter, so increment the depth.
+      // If we've parsed any explicit template parameters, then the depth will
+      // have already been incremented. So we make sure that at most a single
+      // depth level is added.
       if (Actions.getCurGenericLambda())
-        ++CurTemplateDepthTracker;
+        CurTemplateDepthTracker.setAddedDepth(1);
     }
+
     T.consumeClose();
     SourceLocation RParenLoc = T.getCloseLocation();
     SourceLocation DeclEndLoc = RParenLoc;
@@ -1298,6 +1334,7 @@ ExprResult Parser::ParseLambdaExpressionAfterIntroducer(
 
   StmtResult Stmt(ParseCompoundStatementBody());
   BodyScope.Exit();
+  TemplateParamScope.Exit();
 
   if (!Stmt.isInvalid() && !TrailingReturnType.isInvalid())
     return Actions.ActOnLambdaExpr(LambdaBeginLoc, Stmt.get(), getCurScope());
diff --git a/clang/lib/Sema/Sema.cpp b/clang/lib/Sema/Sema.cpp
index 0eb967a641b..8984398eae4 100644
--- a/clang/lib/Sema/Sema.cpp
+++ b/clang/lib/Sema/Sema.cpp
@@ -1793,7 +1793,7 @@ LambdaScopeInfo *Sema::getCurLambda(bool IgnoreNonLambdaCapturingScope) {
 // an associated template parameter list.
 LambdaScopeInfo *Sema::getCurGenericLambda() {
   if (LambdaScopeInfo *LSI =  getCurLambda()) {
-    return (LSI->AutoTemplateParams.size() ||
+    return (LSI->TemplateParams.size() ||
                     LSI->GLTemplateParameterList) ? LSI : nullptr;
   }
   return nullptr;
diff --git a/clang/lib/Sema/SemaLambda.cpp b/clang/lib/Sema/SemaLambda.cpp
index 7ad39fd73ba..1966e9e0803 100644
--- a/clang/lib/Sema/SemaLambda.cpp
+++ b/clang/lib/Sema/SemaLambda.cpp
@@ -20,6 +20,7 @@
 #include "clang/Sema/ScopeInfo.h"
 #include "clang/Sema/SemaInternal.h"
 #include "clang/Sema/SemaLambda.h"
+#include "llvm/ADT/STLExtras.h"
 using namespace clang;
 using namespace sema;
 
@@ -225,19 +226,14 @@ Optional<unsigned> clang::getStackIndexOfNearestEnclosingCaptureCapableLambda(
 
 static inline TemplateParameterList *
 getGenericLambdaTemplateParameterList(LambdaScopeInfo *LSI, Sema &SemaRef) {
-  if (LSI->GLTemplateParameterList)
-    return LSI->GLTemplateParameterList;
-
-  if (!LSI->AutoTemplateParams.empty()) {
-    SourceRange IntroRange = LSI->IntroducerRange;
-    SourceLocation LAngleLoc = IntroRange.getBegin();
-    SourceLocation RAngleLoc = IntroRange.getEnd();
+  if (!LSI->GLTemplateParameterList && !LSI->TemplateParams.empty()) {
     LSI->GLTemplateParameterList = TemplateParameterList::Create(
         SemaRef.Context,
-        /*Template kw loc*/ SourceLocation(), LAngleLoc,
-        llvm::makeArrayRef((NamedDecl *const *)LSI->AutoTemplateParams.data(),
-                           LSI->AutoTemplateParams.size()),
-        RAngleLoc, nullptr);
+        /*Template kw loc*/ SourceLocation(),
+        /*L angle loc*/ LSI->ExplicitTemplateParamsRange.getBegin(),
+        LSI->TemplateParams,
+        /*R angle loc*/LSI->ExplicitTemplateParamsRange.getEnd(),
+        nullptr);
   }
   return LSI->GLTemplateParameterList;
 }
@@ -492,6 +488,23 @@ void Sema::finishLambdaExplicitCaptures(LambdaScopeInfo *LSI) {
   LSI->finishedExplicitCaptures();
 }
 
+void Sema::ActOnLambdaExplicitTemplateParameterList(SourceLocation LAngleLoc,
+                                                    ArrayRef<NamedDecl *> TParams,
+                                                    SourceLocation RAngleLoc) {
+  LambdaScopeInfo *LSI = getCurLambda();
+  assert(LSI && "Expected a lambda scope");
+  assert(LSI->NumExplicitTemplateParams == 0 &&
+         "Already acted on explicit template parameters");
+  assert(LSI->TemplateParams.empty() &&
+         "Explicit template parameters should come "
+         "before invented (auto) ones");
+  assert(!TParams.empty() &&
+         "No template parameters to act on");
+  LSI->TemplateParams.append(TParams.begin(), TParams.end());
+  LSI->NumExplicitTemplateParams = TParams.size();
+  LSI->ExplicitTemplateParamsRange = {LAngleLoc, RAngleLoc};
+}
+
 void Sema::addLambdaParameters(
     ArrayRef<LambdaIntroducer::LambdaCapture> Captures,
     CXXMethodDecl *CallOperator, Scope *CurScope) {
@@ -832,17 +845,23 @@ FieldDecl *Sema::buildInitCaptureField(LambdaScopeInfo *LSI, VarDecl *Var) {
 void Sema::ActOnStartOfLambdaDefinition(LambdaIntroducer &Intro,
                                         Declarator &ParamInfo,
                                         Scope *CurScope) {
-  // Determine if we're within a context where we know that the lambda will
-  // be dependent, because there are template parameters in scope.
-  bool KnownDependent = false;
   LambdaScopeInfo *const LSI = getCurLambda();
   assert(LSI && "LambdaScopeInfo should be on stack!");
 
-  // The lambda-expression's closure type might be dependent even if its
-  // semantic context isn't, if it appears within a default argument of a
-  // function template.
-  if (CurScope->getTemplateParamParent())
-    KnownDependent = true;
+  // Determine if we're within a context where we know that the lambda will
+  // be dependent, because there are template parameters in scope.
+  bool KnownDependent;
+  if (LSI->NumExplicitTemplateParams > 0) {
+    auto *TemplateParamScope = CurScope->getTemplateParamParent();
+    assert(TemplateParamScope &&
+           "Lambda with explicit template param list should establish a "
+           "template param scope");
+    assert(TemplateParamScope->getParent());
+    KnownDependent = TemplateParamScope->getParent()
+                                       ->getTemplateParamParent() != nullptr;
+  } else {
+    KnownDependent = CurScope->getTemplateParamParent() != nullptr;
+  }
 
   // Determine the signature of the call operator.
   TypeSourceInfo *MethodTyInfo;
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
index 3b25595a33a..318c6761731 100644
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -2935,7 +2935,7 @@ static QualType GetDeclSpecTypeForDeclarator(TypeProcessingState &state,
         sema::LambdaScopeInfo *LSI = SemaRef.getCurLambda();
         assert(LSI && "No LambdaScopeInfo on the stack!");
         const unsigned TemplateParameterDepth = LSI->AutoTemplateParameterDepth;
-        const unsigned AutoParameterPosition = LSI->AutoTemplateParams.size();
+        const unsigned AutoParameterPosition = LSI->TemplateParams.size();
         const bool IsParameterPack = D.hasEllipsis();
 
         // Create the TemplateTypeParmDecl here to retrieve the corresponding
@@ -2947,7 +2947,8 @@ static QualType GetDeclSpecTypeForDeclarator(TypeProcessingState &state,
                 /*KeyLoc*/ SourceLocation(), /*NameLoc*/ D.getBeginLoc(),
                 TemplateParameterDepth, AutoParameterPosition,
                 /*Identifier*/ nullptr, false, IsParameterPack);
-        LSI->AutoTemplateParams.push_back(CorrespondingTemplateParam);
+        CorrespondingTemplateParam->setImplicit();
+        LSI->TemplateParams.push_back(CorrespondingTemplateParam);
         // Replace the 'auto' in the function parameter with this invented
         // template type parameter.
         // FIXME: Retain some type sugar to indicate that this was written