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

3 files changed, 6 insertions, 1 deletions

diff --git a/clang/lib/Serialization/ASTReader.cpp b/clang/lib/Serialization/ASTReader.cpp
index 462c2d3db97..5b1a608e600 100644
--- a/clang/lib/Serialization/ASTReader.cpp
+++ b/clang/lib/Serialization/ASTReader.cpp
@@ -4740,7 +4740,9 @@ QualType ASTReader::readTypeRecord(unsigned Index) {
     QualType Deduced = readType(*Loc.F, Record, Idx);
     bool IsDecltypeAuto = Record[Idx++];
     bool IsDependent = Deduced.isNull() ? Record[Idx++] : false;
-    return Context.getAutoType(Deduced, IsDecltypeAuto, IsDependent);
+    bool IsParameterPack = Record[Idx++];
+    return Context.getAutoType(Deduced, IsDecltypeAuto, IsDependent, 
+                                                      IsParameterPack);
   }
 
   case TYPE_RECORD: {
diff --git a/clang/lib/Serialization/ASTReaderDecl.cpp b/clang/lib/Serialization/ASTReaderDecl.cpp
index 7099d32b3d5..74e99379a4b 100644
--- a/clang/lib/Serialization/ASTReaderDecl.cpp
+++ b/clang/lib/Serialization/ASTReaderDecl.cpp
@@ -1201,6 +1201,7 @@ void ASTDeclReader::ReadCXXDefinitionData(
       = (Capture*)Reader.Context.Allocate(sizeof(Capture)*Lambda.NumCaptures);
     Capture *ToCapture = Lambda.Captures;
     Lambda.MethodTyInfo = GetTypeSourceInfo(Record, Idx);
+    Lambda.TheLambdaExpr = cast<LambdaExpr>(Reader.ReadExpr(F));
     for (unsigned I = 0, N = Lambda.NumCaptures; I != N; ++I) {
       SourceLocation Loc = ReadSourceLocation(Record, Idx);
       bool IsImplicit = Record[Idx++];
diff --git a/clang/lib/Serialization/ASTWriter.cpp b/clang/lib/Serialization/ASTWriter.cpp
index d8485300bec..01bc9cbc377 100644
--- a/clang/lib/Serialization/ASTWriter.cpp
+++ b/clang/lib/Serialization/ASTWriter.cpp
@@ -253,6 +253,7 @@ void ASTTypeWriter::VisitAutoType(const AutoType *T) {
   Record.push_back(T->isDecltypeAuto());
   if (T->getDeducedType().isNull())
     Record.push_back(T->isDependentType());
+  Record.push_back(T->containsUnexpandedParameterPack());
   Code = TYPE_AUTO;
 }
 
@@ -5136,6 +5137,7 @@ void ASTWriter::AddCXXDefinitionData(const CXXRecordDecl *D, RecordDataImpl &Rec
     Record.push_back(Lambda.ManglingNumber);
     AddDeclRef(Lambda.ContextDecl, Record);
     AddTypeSourceInfo(Lambda.MethodTyInfo, Record);
+    AddStmt(Lambda.TheLambdaExpr);
     for (unsigned I = 0, N = Lambda.NumCaptures; I != N; ++I) {
       LambdaExpr::Capture &Capture = Lambda.Captures[I];
       AddSourceLocation(Capture.getLocation(), Record);