Implement a rudimentary form of generic lambdas.

Specifically, the following features are not included in this commit:
  - any sort of capturing within generic lambdas 
  - nested lambdas
  - conversion operator for captureless lambdas
  - ensuring all visitors are generic lambda aware


As an example of what compiles:

template <class F1, class F2>
struct overload : F1, F2 {
    using F1::operator();
    using F2::operator();
    overload(F1 f1, F2 f2) : F1(f1), F2(f2) { }
  };

  auto Recursive = [](auto Self, auto h, auto ... rest) {
    return 1 + Self(Self, rest...);
  };
  auto Base = [](auto Self, auto h) {
      return 1;
  };
  overload<decltype(Base), decltype(Recursive)> O(Base, Recursive);
  int num_params =  O(O, 5, 3, "abc", 3.14, 'a');

Please see attached tests for more examples.

Some implementation notes:

  - Add a new Declarator context => LambdaExprParameterContext to 
    clang::Declarator to allow the use of 'auto' in declaring generic
    lambda parameters
    
  - Augment AutoType's constructor (similar to how variadic 
    template-type-parameters ala TemplateTypeParmDecl are implemented) to 
    accept an IsParameterPack to encode a generic lambda parameter pack.
  
  - Add various helpers to CXXRecordDecl to facilitate identifying
    and querying a closure class
  
  - LambdaScopeInfo (which maintains the current lambda's Sema state)
    was augmented to house the current depth of the template being
    parsed (id est the Parser calls Sema::RecordParsingTemplateParameterDepth)
    so that Sema::ActOnLambdaAutoParameter may use it to create the 
    appropriate list of corresponding TemplateTypeParmDecl for each
    auto parameter identified within the generic lambda (also stored
    within the current LambdaScopeInfo).  Additionally, 
    a TemplateParameterList data-member was added to hold the invented
    TemplateParameterList AST node which will be much more useful
    once we teach TreeTransform how to transform generic lambdas.
    
  - SemaLambda.h was added to hold some common lambda utility
    functions (this file is likely to grow ...)
    
  - Teach Sema::ActOnStartOfFunctionDef to check whether it
    is being called to instantiate a generic lambda's call
    operator, and if so, push an appropriately prepared
    LambdaScopeInfo object on the stack.
    
  - Teach Sema::ActOnStartOfLambdaDefinition to set the
    return type of a lambda without a trailing return type
    to 'auto' in C++1y mode, and teach the return type
    deduction machinery in SemaStmt.cpp to process either
    C++11 and C++14 lambda's correctly depending on the flag.    

  - various tests were added - but much more will be needed.

A greatful thanks to all reviewers including Eli Friedman,  
James Dennett and the ever illuminating Richard Smith.  And 
yet I am certain that I have allowed unidentified bugs to creep in; 
bugs, that I will do my best to slay, once identified!

Thanks!

llvm-svn: 188977

5 files changed, 69 insertions, 15 deletions

diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 29ddb37525d..b1b52fb1c57 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -3649,20 +3649,24 @@ QualType ASTContext::getUnaryTransformType(QualType BaseType,
 /// deduced to the given type, or to the canonical undeduced 'auto' type, or the
 /// canonical deduced-but-dependent 'auto' type.
 QualType ASTContext::getAutoType(QualType DeducedType, bool IsDecltypeAuto,
-                                 bool IsDependent) const {
-  if (DeducedType.isNull() && !IsDecltypeAuto && !IsDependent)
+                             bool IsDependent, bool IsParameterPack) const {
+  if (DeducedType.isNull() && !IsDecltypeAuto && !IsDependent && 
+                              !IsParameterPack)
     return getAutoDeductType();
-
+  assert(!IsParameterPack || DeducedType.isNull() 
+           && "Auto parameter pack: auto ... a should always be undeduced!");
   // Look in the folding set for an existing type.
   void *InsertPos = 0;
   llvm::FoldingSetNodeID ID;
-  AutoType::Profile(ID, DeducedType, IsDecltypeAuto, IsDependent);
+  AutoType::Profile(ID, DeducedType, IsDecltypeAuto, IsDependent, 
+     IsParameterPack);
   if (AutoType *AT = AutoTypes.FindNodeOrInsertPos(ID, InsertPos))
     return QualType(AT, 0);
 
   AutoType *AT = new (*this, TypeAlignment) AutoType(DeducedType,
                                                      IsDecltypeAuto,
-                                                     IsDependent);
+                                                     IsDependent, 
+                                                     IsParameterPack);
   Types.push_back(AT);
   if (InsertPos)
     AutoTypes.InsertNode(AT, InsertPos);
@@ -3702,7 +3706,8 @@ QualType ASTContext::getAutoDeductType() const {
   if (AutoDeductTy.isNull())
     AutoDeductTy = QualType(
       new (*this, TypeAlignment) AutoType(QualType(), /*decltype(auto)*/false,
-                                          /*dependent*/false),
+                                          /*dependent*/false, 
+                                          /*IsParameterPack*/false),
       0);
   return AutoDeductTy;
 }
diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 922172701f0..f03b66dfd88 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -1709,7 +1709,9 @@ QualType ASTNodeImporter::VisitAutoType(const AutoType *T) {
       return QualType();
   }
   
-  return Importer.getToContext().getAutoType(ToDeduced, T->isDecltypeAuto());
+  return Importer.getToContext().getAutoType(ToDeduced, T->isDecltypeAuto(), 
+                                             /*IsDependent*/false,
+                                      T->containsUnexpandedParameterPack());
 }
 
 QualType ASTNodeImporter::VisitRecordType(const RecordType *T) {
diff --git a/clang/lib/AST/DeclCXX.cpp b/clang/lib/AST/DeclCXX.cpp
index ccd8220a684..b50aa9337fe 100644
--- a/clang/lib/AST/DeclCXX.cpp
+++ b/clang/lib/AST/DeclCXX.cpp
@@ -20,6 +20,7 @@
 #include "clang/AST/ExprCXX.h"
 #include "clang/AST/TypeLoc.h"
 #include "clang/Basic/IdentifierTable.h"
+#include "clang/Sema/SemaLambda.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallPtrSet.h"
 using namespace clang;
@@ -930,6 +931,40 @@ bool CXXRecordDecl::isCLike() const {
   return isPOD() && data().HasOnlyCMembers;
 }
 
+bool CXXRecordDecl::isGenericLambda() const { 
+  return isLambda() && 
+      getLambdaCallOperator()->getDescribedFunctionTemplate(); 
+}
+
+CXXMethodDecl* CXXRecordDecl::getLambdaCallOperator() const {
+  if (!isLambda()) return 0;
+  DeclarationName Name = 

+    getASTContext().DeclarationNames.getCXXOperatorName(OO_Call);

+  DeclContext::lookup_const_result Calls = lookup(Name);
+

+  assert(!Calls.empty() && "Missing lambda call operator!");

+  assert(Calls.size() == 1 && "More than one lambda call operator!"); 

+   

+  NamedDecl *CallOp = Calls.front();

+  if (FunctionTemplateDecl *CallOpTmpl = 

+                    dyn_cast<FunctionTemplateDecl>(CallOp)) 

+    return cast<CXXMethodDecl>(CallOpTmpl->getTemplatedDecl());

+  
+  return cast<CXXMethodDecl>(CallOp);
+}
+
+CXXMethodDecl* CXXRecordDecl::getLambdaStaticInvoker() const {
+  if (!isLambda()) return 0;
+  DeclarationName Name = 

+    &getASTContext().Idents.get(getLambdaStaticInvokerName());

+  DeclContext::lookup_const_result Invoker = lookup(Name);
+  if (Invoker.empty()) return 0;

+  assert(Invoker.size() == 1 && "More than one static invoker operator!");  

+  CXXMethodDecl *Result = cast<CXXMethodDecl>(Invoker.front());  

+  return Result;
+
+}
+
 void CXXRecordDecl::getCaptureFields(
        llvm::DenseMap<const VarDecl *, FieldDecl *> &Captures,
        FieldDecl *&ThisCapture) const {
@@ -947,6 +982,14 @@ void CXXRecordDecl::getCaptureFields(
   }
 }
 
+TemplateParameterList* 
+        CXXRecordDecl::getGenericLambdaTemplateParameterList() const {
+  if (!isLambda()) return 0;
+  CXXMethodDecl *CallOp = getLambdaCallOperator();     
+  if (FunctionTemplateDecl *Tmpl = CallOp->getDescribedFunctionTemplate())
+    return Tmpl->getTemplateParameters();
+  return 0;
+}
 
 static CanQualType GetConversionType(ASTContext &Context, NamedDecl *Conv) {
   QualType T;
@@ -1493,7 +1536,7 @@ bool CXXMethodDecl::hasInlineBody() const {
 
 bool CXXMethodDecl::isLambdaStaticInvoker() const {
   return getParent()->isLambda() && 
-         getIdentifier() && getIdentifier()->getName() == "__invoke";
+         getParent()->getLambdaStaticInvoker() == this;
 }
 
 
diff --git a/clang/lib/AST/ExprCXX.cpp b/clang/lib/AST/ExprCXX.cpp
index 0609eb1d65d..28794d4f621 100644
--- a/clang/lib/AST/ExprCXX.cpp
+++ b/clang/lib/AST/ExprCXX.cpp
@@ -1026,13 +1026,13 @@ CXXRecordDecl *LambdaExpr::getLambdaClass() const {
 
 CXXMethodDecl *LambdaExpr::getCallOperator() const {
   CXXRecordDecl *Record = getLambdaClass();
-  DeclarationName Name
-    = Record->getASTContext().DeclarationNames.getCXXOperatorName(OO_Call);
-  DeclContext::lookup_result Calls = Record->lookup(Name);
-  assert(!Calls.empty() && "Missing lambda call operator!");
-  assert(Calls.size() == 1 && "More than one lambda call operator!");
-  CXXMethodDecl *Result = cast<CXXMethodDecl>(Calls.front());
-  return Result;
+  return Record->getLambdaCallOperator();  
+}
+
+TemplateParameterList *LambdaExpr::getTemplateParameterList() const {
+  CXXRecordDecl *Record = getLambdaClass();
+  return Record->getGenericLambdaTemplateParameterList();
+
 }
 
 CompoundStmt *LambdaExpr::getBody() const {
diff --git a/clang/lib/AST/Type.cpp b/clang/lib/AST/Type.cpp
index 44da348b0b7..bb6d0bf05d1 100644
--- a/clang/lib/AST/Type.cpp
+++ b/clang/lib/AST/Type.cpp
@@ -589,6 +589,10 @@ namespace {
     AutoType *VisitAttributedType(const AttributedType *T) {
       return Visit(T->getModifiedType());
     }
+    AutoType *VisitPackExpansionType(const PackExpansionType *T) {
+      return Visit(T->getPattern());
+    }
+
   };
 }