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

1 files changed, 21 insertions, 5 deletions

diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index 9e5738394ea..6e69bdc5128 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -782,7 +782,10 @@ public:
     // Note, IsDependent is always false here: we implicitly convert an 'auto'
     // which has been deduced to a dependent type into an undeduced 'auto', so
     // that we'll retry deduction after the transformation.
-    return SemaRef.Context.getAutoType(Deduced, IsDecltypeAuto);
+    // FIXME: Can we assume the same about IsParameterPack?
+    return SemaRef.Context.getAutoType(Deduced, IsDecltypeAuto, 
+                                       /*IsDependent*/ false, 
+                                       /*IsParameterPack*/ false);
   }
 
   /// \brief Build a new template specialization type.
@@ -3494,7 +3497,9 @@ TreeTransform<Derived>::TransformQualifiedType(TypeLocBuilder &TLB,
         Qs.removeObjCLifetime();
         Deduced = SemaRef.Context.getQualifiedType(Deduced.getUnqualifiedType(),
                                                    Qs);
-        Result = SemaRef.Context.getAutoType(Deduced, AutoTy->isDecltypeAuto());
+        Result = SemaRef.Context.getAutoType(Deduced, AutoTy->isDecltypeAuto(), 
+                                AutoTy->isDependentType(), 
+                                AutoTy->containsUnexpandedParameterPack());
         TLB.TypeWasModifiedSafely(Result);
       } else {
         // Otherwise, complain about the addition of a qualifier to an
@@ -8193,6 +8198,14 @@ TreeTransform<Derived>::TransformCXXTemporaryObjectExpr(
 template<typename Derived>
 ExprResult
 TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
+ 
+  // FIXME: Implement nested generic lambda transformations.
+  if (E->isGenericLambda()) {
+    getSema().Diag(E->getIntroducerRange().getBegin(), 
+      diag::err_glambda_not_fully_implemented) 
+      << " nested lambdas not implemented yet";
+    return ExprError();
+  }
   // Transform the type of the lambda parameters and start the definition of
   // the lambda itself.
   TypeSourceInfo *MethodTy
@@ -8215,7 +8228,10 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
         E->getCallOperator()->param_size(),
         0, ParamTypes, &Params))
     return ExprError();
-
+  getSema().PushLambdaScope();
+  LambdaScopeInfo *LSI = getSema().getCurLambda();
+  // TODO: Fix for nested lambdas
+  LSI->GLTemplateParameterList = 0;
   // Build the call operator.
   CXXMethodDecl *CallOperator
     = getSema().startLambdaDefinition(Class, E->getIntroducerRange(),
@@ -8250,9 +8266,9 @@ TreeTransform<Derived>::TransformLambdaScope(LambdaExpr *E,
   // Introduce the context of the call operator.
   Sema::ContextRAII SavedContext(getSema(), CallOperator);
 
+  LambdaScopeInfo *const LSI = getSema().getCurLambda();
   // Enter the scope of the lambda.
-  sema::LambdaScopeInfo *LSI
-    = getSema().enterLambdaScope(CallOperator, E->getIntroducerRange(),
+  getSema().buildLambdaScope(LSI, CallOperator, E->getIntroducerRange(),
                                  E->getCaptureDefault(),
                                  E->getCaptureDefaultLoc(),
                                  E->hasExplicitParameters(),