From 7c3c6bca2662704fbe038137d8ef2e4112359586 Mon Sep 17 00:00:00 2001
From: Eli Friedman <eli.friedman@gmail.com>
Date: Thu, 20 Sep 2012 01:40:23 +0000
Subject: [PATCH] Handle lambdas where the lambda-declarator is an explicit
 "(void)".  PR13854.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@164274 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/clang/Sema/Sema.h           |  1 +
 lib/Sema/SemaDecl.cpp               | 32 +++++++++++++++--------------
 lib/Sema/SemaLambda.cpp             | 12 ++++++++---
 test/SemaCXX/lambda-expressions.cpp |  4 ++++
 4 files changed, 31 insertions(+), 18 deletions(-)

diff --git a/include/clang/Sema/Sema.h b/include/clang/Sema/Sema.h
index 4798b032df..391a6d33b2 100644
--- a/include/clang/Sema/Sema.h
+++ b/include/clang/Sema/Sema.h
@@ -1273,6 +1273,7 @@ public:
                                      MultiTemplateParamsArg TemplateParamLists,
                                      bool &AddToScope);
   bool AddOverriddenMethods(CXXRecordDecl *DC, CXXMethodDecl *MD);
+  void checkVoidParamDecl(ParmVarDecl *Param);
 
   bool CheckConstexprFunctionDecl(const FunctionDecl *FD);
   bool CheckConstexprFunctionBody(const FunctionDecl *FD, Stmt *Body);
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 83dc86f575..2dd5df1ea0 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -5128,6 +5128,22 @@ static FunctionDecl* CreateNewFunctionDecl(Sema &SemaRef, Declarator &D,
   }
 }
 
+void Sema::checkVoidParamDecl(ParmVarDecl *Param) {
+  // In C++, the empty parameter-type-list must be spelled "void"; a
+  // typedef of void is not permitted.
+  if (getLangOpts().CPlusPlus &&
+      Param->getType().getUnqualifiedType() != Context.VoidTy) {
+    bool IsTypeAlias = false;
+    if (const TypedefType *TT = Param->getType()->getAs<TypedefType>())
+      IsTypeAlias = isa<TypeAliasDecl>(TT->getDecl());
+    else if (const TemplateSpecializationType *TST =
+               Param->getType()->getAs<TemplateSpecializationType>())
+      IsTypeAlias = TST->isTypeAlias();
+    Diag(Param->getLocation(), diag::err_param_typedef_of_void)
+      << IsTypeAlias;
+  }
+}
+
 NamedDecl*
 Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
                               TypeSourceInfo *TInfo, LookupResult &Previous,
@@ -5477,21 +5493,7 @@ Sema::ActOnFunctionDeclarator(Scope *S, Declarator &D, DeclContext *DC,
         FTI.ArgInfo[0].Param &&
         cast<ParmVarDecl>(FTI.ArgInfo[0].Param)->getType()->isVoidType()) {
       // Empty arg list, don't push any params.
-      ParmVarDecl *Param = cast<ParmVarDecl>(FTI.ArgInfo[0].Param);
-
-      // In C++, the empty parameter-type-list must be spelled "void"; a
-      // typedef of void is not permitted.
-      if (getLangOpts().CPlusPlus &&
-          Param->getType().getUnqualifiedType() != Context.VoidTy) {
-        bool IsTypeAlias = false;
-        if (const TypedefType *TT = Param->getType()->getAs<TypedefType>())
-          IsTypeAlias = isa<TypeAliasDecl>(TT->getDecl());
-        else if (const TemplateSpecializationType *TST =
-                   Param->getType()->getAs<TemplateSpecializationType>())
-          IsTypeAlias = TST->isTypeAlias();
-        Diag(Param->getLocation(), diag::err_param_typedef_of_void)
-          << IsTypeAlias;
-      }
+      checkVoidParamDecl(cast<ParmVarDecl>(FTI.ArgInfo[0].Param));
     } else if (FTI.NumArgs > 0 && FTI.ArgInfo[0].Param != 0) {
       for (unsigned i = 0, e = FTI.NumArgs; i != e; ++i) {
         ParmVarDecl *Param = cast<ParmVarDecl>(FTI.ArgInfo[i].Param);
diff --git a/lib/Sema/SemaLambda.cpp b/lib/Sema/SemaLambda.cpp
index 489c895c99..15cd2a73e7 100644
--- a/lib/Sema/SemaLambda.cpp
+++ b/lib/Sema/SemaLambda.cpp
@@ -410,9 +410,15 @@ void Sema::ActOnStartOfLambdaDefinition(LambdaIntroducer &Intro,
       = MethodTyInfo->getType()->getAs<FunctionType>()->getResultType() 
                                                         != Context.DependentTy;
 
-    Params.reserve(FTI.NumArgs);
-    for (unsigned i = 0, e = FTI.NumArgs; i != e; ++i)
-      Params.push_back(cast<ParmVarDecl>(FTI.ArgInfo[i].Param));
+    if (FTI.NumArgs == 1 && !FTI.isVariadic && FTI.ArgInfo[0].Ident == 0 &&
+        cast<ParmVarDecl>(FTI.ArgInfo[0].Param)->getType()->isVoidType()) {
+      // Empty arg list, don't push any params.
+      checkVoidParamDecl(cast<ParmVarDecl>(FTI.ArgInfo[0].Param));
+    } else {
+      Params.reserve(FTI.NumArgs);
+      for (unsigned i = 0, e = FTI.NumArgs; i != e; ++i)
+        Params.push_back(cast<ParmVarDecl>(FTI.ArgInfo[i].Param));
+    }
 
     // Check for unexpanded parameter packs in the method type.
     if (MethodTyInfo->getType()->containsUnexpandedParameterPack())
diff --git a/test/SemaCXX/lambda-expressions.cpp b/test/SemaCXX/lambda-expressions.cpp
index 0a95680478..babe743c65 100644
--- a/test/SemaCXX/lambda-expressions.cpp
+++ b/test/SemaCXX/lambda-expressions.cpp
@@ -229,3 +229,7 @@ namespace PR13860 {
     static_assert(sizeof(y), "");
   }
 }
+
+namespace PR13854 {
+  auto l = [](void){};
+}