Support explicit template arguments with variadic generic lambdas

[faisalv]

Summary

Currently clang-trunk crashes on the following:

auto L = [](auto ... v) { };
L.operator()<int>(3);

The reason is that the partially-substituted-pack is incorrectly retained within the current-instantiation-scope
during template-argument-finalization, and because lambda's are local, there parent instantiation
scopes are merged, which leads to the expansion-pattern being retained in the finalized specialization.

This patch ensures that once we have finalized deduction of a parameter-pack, we remove the partially-substituted-pack
so that it doesn't cause CheckParameterPacksForExpansion to incorrectly inform the caller that it needs to retain the expansion pattern.

Thanks!

[rsmith]

LGTM with a simplification.

lib/Sema/SemaTemplateDeduction.cpp

2807–2810

You don't need to pass these unused pointer args. Just:

if (Param->isParameterPack() && CurrentInstantiationScope &&
    CurrentInstantiationScope->getPartiallySubstitutedPack() == Param)
  CurrentInstantiationScope->ResetPartiallySubstitutedPack();

... should do the trick.

[faisalv]

Committed as r209992
http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20140526/106793.html

lib/Sema/SemaTemplateDeduction.cpp

         // argument, because it was explicitly-specified. Just record the
         // presence of this argument.
         Builder.push_back(Deduced[I]);
+        // We may have had explicitly-specified template arguments for a
+        // template parameter pack (that may or may not have been extended 
+        // via additional deduced arguments).
+        if (Param->isParameterPack() && CurrentInstantiationScope) {
+          const TemplateArgument *ExplicitArgs;
+          unsigned NumExplicitArgs;
+          if (CurrentInstantiationScope->getPartiallySubstitutedPack(&ExplicitArgs,
+                  &NumExplicitArgs) == Param) {
+            // Forget the partially-substituted pack; it's substitution is now
+            // complete.
+            CurrentInstantiationScope->ResetPartiallySubstitutedPack();
+          }
+        }
         continue;
       }
 

test/SemaCXX/cxx1y-generic-lambdas-variadics.cpp

+// RUN: %clang_cc1 -std=c++1y -verify -fsyntax-only -fblocks -emit-llvm-only %s
+// RUN: %clang_cc1 -std=c++1y -verify -fsyntax-only -fblocks -fdelayed-template-parsing %s -DDELAYED_TEMPLATE_PARSING
+// RUN: %clang_cc1 -std=c++1y -verify -fsyntax-only -fblocks -fms-extensions %s -DMS_EXTENSIONS
+// RUN: %clang_cc1 -std=c++1y -verify -fsyntax-only -fblocks -fdelayed-template-parsing -fms-extensions %s -DMS_EXTENSIONS -DDELAYED_TEMPLATE_PARSING
+
+namespace explicit_argument_variadics {
+
+
+template<class ... Ts> void print(Ts ... ) { }
+
+struct X { };
+struct Y { };
+struct Z { };
+
+int test() { 
+  {
+    auto L = [](auto ... as) { };
+    L.operator()<bool>(true);
+  }
+  {
+    auto L = [](auto a) { };
+    L.operator()<bool>(false);
+  }
+  {
+    auto L = [](auto a, auto b) { };
+    L.operator()<bool>(false, 'a');
+  }
+  {
+    auto L = [](auto a, auto b) { };
+    L.operator()<bool, char>(false, 'a');
+  }
+  {
+    auto L = [](auto a, auto b, auto ... cs) { };
+    L.operator()<bool, char>(false, 'a');
+    L.operator()<bool, char, const char*>(false, 'a', "jim");    
+  }
+
+  {
+    auto L = [](auto ... As) {
+    };
+    L.operator()<bool, double>(false, 3.14, "abc");
+  }
+  {
+    auto L = [](auto A, auto B, auto ... As) {
+    };
+    L.operator()<bool>(false, 3.14, "abc");
+    L.operator()<bool, char>(false, 3.14, "abc"); //expected-warning{{implicit conversion}}
+    L.operator()<X, Y, bool, Z>(X{}, Y{}, 3.14, Z{}, X{}); //expected-warning{{implicit conversion}}
+  }
+  {
+    auto L = [](auto ... As) {
+      print("\nL::As = ", As ...);
+      return [](decltype(As) ... as, auto ... Bs) {
+        print("\nL::Inner::as = ", as ...);
+        print("\nL::Inner::Bs = ", Bs ...);
+        return 4;
+      };
+    };
+    auto M = L.operator()<bool, double>(false, 3.14, "abc");
+    M(false, 6.26, "jim", true);
+    M.operator()<bool>(true, 6.26, "jim", false, 3.14);
+  }
+  {
+    auto L = [](auto A, auto ... As) {
+      print("\nL::As = ", As ...);
+      return [](decltype(As) ... as, decltype(A) a, auto ... Bs) {
+        print("\nL::Inner::as = ", as ...);
+        print("\nL::Inner::Bs = ", Bs ...);
+        return 4;
+      };
+    };
+    auto M = L.operator()<bool, double>(false, 3.14, "abc");
+    M(6.26, "jim", true);
+    M.operator()<X>(6.26, "jim", false, X{}, Y{}, Z{});
+  }
+  
+  return 0;
+}
+ int run = test();
+} // end ns explicit_argument_extension
 No newline at end of file