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, 135 insertions, 0 deletions

diff --git a/clang/test/CXX/expr/expr.prim/expr.prim.lambda/p5-generic-lambda-1y.cpp b/clang/test/CXX/expr/expr.prim/expr.prim.lambda/p5-generic-lambda-1y.cpp
new file mode 100644
index 00000000000..c1311617efb
--- /dev/null
+++ b/clang/test/CXX/expr/expr.prim/expr.prim.lambda/p5-generic-lambda-1y.cpp
@@ -0,0 +1,135 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s -std=c++1y -DCXX1Y -emit-llvm

+

+namespace test_factorial {

+

+auto Fact = [](auto Self, unsigned n) -> unsigned {

+    return !n ? 1 : Self(Self, n - 1) * n;

+};

+

+auto six = Fact(Fact, 3);

+

+}

+

+namespace overload_generic_lambda {

+  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 NumParams = [](auto Self, auto h, auto ... rest) -> unsigned {

+    return 1 + Self(Self, rest...);

+  };

+  auto Base = [](auto Self, auto h) -> unsigned {

+      return 1;

+  };

+  overload<decltype(Base), decltype(NumParams)> O(Base, NumParams);

+  int num_params =  O(O, 5, 3, "abc", 3.14, 'a');

+}

+

+

+namespace overload_generic_lambda_return_type_deduction {

+  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 NumParams = [](auto Self, auto h, auto ... rest) {

+    return 1 + Self(Self, rest...);

+  };

+  auto Base = [](auto Self, auto h) {

+      return 1;

+  };

+  overload<decltype(Base), decltype(NumParams)> O(Base, NumParams);

+  int num_params =  O(O, 5, 3, "abc", 3.14, 'a');

+}

+

+namespace test_standard_p5 {

+// FIXME: This test should eventually compile without an explicit trailing return type

+auto glambda = [](auto a, auto&& b) ->bool { return a < b; };

+bool b = glambda(3, 3.14); // OK

+

+}

+namespace test_deduction_failure {

+ int test() {

+   auto g = [](auto *a) { //expected-note{{candidate template ignored}}

+    return a;

+   };

+   struct X { };

+   X *x;

+   g(x);

+   g(3); //expected-error{{no matching function}}

+   return 0;

+ }

+

+}

+  

+namespace test_instantiation_or_sfinae_failure {

+int test2() {

+  {

+    auto L = [](auto *a) { 

+                return (*a)(a); }; //expected-error{{called object type 'double' is not a function}}

+    //l(&l);

+    double d;

+    L(&d); //expected-note{{in instantiation of}}

+    auto M = [](auto b) { return b; };

+    L(&M); // ok

+  }

+  {

+    auto L = [](auto *a) ->decltype (a->foo()) { //expected-note2{{candidate template ignored:}}

+                return (*a)(a); }; 

+    //l(&l);

+    double d;

+    L(&d); //expected-error{{no matching function for call}} 

+    auto M = [](auto b) { return b; };

+    L(&M); //expected-error{{no matching function for call}} 

+ 

+  }

+  return 0;

+}

+

+

+}

+  

+namespace test_misc {

+auto GL = [](auto a, decltype(a) b) //expected-note{{candidate function}} 

+                -> int { return a + b; };

+

+void test() {

+   struct X { };

+   GL(3, X{}); //expected-error{{no matching function}}

+}

+

+void test2() {

+  auto l = [](auto *a) -> int { 

+              (*a)(a); return 0; }; //expected-error{{called object type 'double' is not a function}}

+  l(&l);

+  double d;

+  l(&d); //expected-note{{in instantiation of}}

+}

+

+}

+

+namespace nested_lambdas {

+  int test() {

+    auto L = [](auto a) {

+                 return [=](auto b) {  //expected-error{{unimplemented}}

+                           return a + b;

+                        };

+              };

+   // auto M = L(3.14);

+   // return M('4');    

+  }

+  auto get_lambda() {

+    return [](auto a) {

+      return a; 

+    };

+  };

+  

+  int test2() {

+    auto L = get_lambda();

+    L(3);

+  }

+}

+