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, 20 insertions, 15 deletions

diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
index 392535acef2..4c4ce874822 100644
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -4670,6 +4670,7 @@ void Parser::ParseDirectDeclarator(Declarator &D) {
     //   as part of the parameter-declaration-clause.
     if (Tok.is(tok::ellipsis) && D.getCXXScopeSpec().isEmpty() &&
         !((D.getContext() == Declarator::PrototypeContext ||
+           D.getContext() == Declarator::LambdaExprParameterContext ||
            D.getContext() == Declarator::BlockLiteralContext) &&
           NextToken().is(tok::r_paren) &&
           !D.hasGroupingParens() &&
@@ -4988,7 +4989,6 @@ void Parser::ParseFunctionDeclarator(Declarator &D,
   TypeResult TrailingReturnType;
 
   Actions.ActOnStartFunctionDeclarator();
-
   /* LocalEndLoc is the end location for the local FunctionTypeLoc.
      EndLoc is the end location for the function declarator.
      They differ for trailing return types. */
@@ -5009,7 +5009,8 @@ void Parser::ParseFunctionDeclarator(Declarator &D,
     EndLoc = RParenLoc;
   } else {
     if (Tok.isNot(tok::r_paren))
-      ParseParameterDeclarationClause(D, FirstArgAttrs, ParamInfo, EllipsisLoc);
+      ParseParameterDeclarationClause(D, FirstArgAttrs, ParamInfo, 
+                                      EllipsisLoc);
     else if (RequiresArg)
       Diag(Tok, diag::err_argument_required_after_attribute);
 
@@ -5240,7 +5241,6 @@ void Parser::ParseParameterDeclarationClause(
        ParsedAttributes &FirstArgAttrs,
        SmallVectorImpl<DeclaratorChunk::ParamInfo> &ParamInfo,
        SourceLocation &EllipsisLoc) {
-
   while (1) {
     if (Tok.is(tok::ellipsis)) {
       // FIXME: Issue a diagnostic if we parsed an attribute-specifier-seq
@@ -5270,16 +5270,21 @@ void Parser::ParseParameterDeclarationClause(
 
     ParseDeclarationSpecifiers(DS);
 
-    // Parse the declarator.  This is "PrototypeContext", because we must
-    // accept either 'declarator' or 'abstract-declarator' here.
-    Declarator ParmDecl(DS, Declarator::PrototypeContext);
-    ParseDeclarator(ParmDecl);
+
+    // Parse the declarator.  This is "PrototypeContext" or 
+    // "LambdaExprParameterContext", because we must accept either 
+    // 'declarator' or 'abstract-declarator' here.
+    Declarator ParmDeclarator(DS, 
+              D.getContext() == Declarator::LambdaExprContext ?
+                                  Declarator::LambdaExprParameterContext : 
+                                                Declarator::PrototypeContext);
+    ParseDeclarator(ParmDeclarator);
 
     // Parse GNU attributes, if present.
-    MaybeParseGNUAttributes(ParmDecl);
+    MaybeParseGNUAttributes(ParmDeclarator);
 
     // Remember this parsed parameter in ParamInfo.
-    IdentifierInfo *ParmII = ParmDecl.getIdentifier();
+    IdentifierInfo *ParmII = ParmDeclarator.getIdentifier();
 
     // DefArgToks is used when the parsing of default arguments needs
     // to be delayed.
@@ -5287,8 +5292,8 @@ void Parser::ParseParameterDeclarationClause(
 
     // If no parameter was specified, verify that *something* was specified,
     // otherwise we have a missing type and identifier.
-    if (DS.isEmpty() && ParmDecl.getIdentifier() == 0 &&
-        ParmDecl.getNumTypeObjects() == 0) {
+    if (DS.isEmpty() && ParmDeclarator.getIdentifier() == 0 &&
+        ParmDeclarator.getNumTypeObjects() == 0) {
       // Completely missing, emit error.
       Diag(DSStart, diag::err_missing_param);
     } else {
@@ -5297,8 +5302,8 @@ void Parser::ParseParameterDeclarationClause(
 
       // Inform the actions module about the parameter declarator, so it gets
       // added to the current scope.
-      Decl *Param = Actions.ActOnParamDeclarator(getCurScope(), ParmDecl);
-
+      Decl *Param = Actions.ActOnParamDeclarator(getCurScope(), 
+                                                       ParmDeclarator);
       // Parse the default argument, if any. We parse the default
       // arguments in all dialects; the semantic analysis in
       // ActOnParamDefaultArgument will reject the default argument in
@@ -5359,8 +5364,8 @@ void Parser::ParseParameterDeclarationClause(
       }
 
       ParamInfo.push_back(DeclaratorChunk::ParamInfo(ParmII,
-                                          ParmDecl.getIdentifierLoc(), Param,
-                                          DefArgToks));
+                                          ParmDeclarator.getIdentifierLoc(), 
+                                          Param, DefArgToks));
     }
 
     // If the next token is a comma, consume it and keep reading arguments.