From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Tue, 2 Feb 2016 23:58:56 +0000 (+0000)
Subject: PR24989: Stop trying to use the C++11 rules for lambda return type inference in
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=3e08674e1c5ed78603f1d527e0fee5d089ce4d99;p=clang

PR24989: Stop trying to use the C++11 rules for lambda return type inference in
C++14 generic lambdas. It conflicts with the C++14 return type deduction
mechanism, and results in us failing to actually deduce the lambda's return
type in some cases.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@259609 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index ffd71e38c6..510e70aedb 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -11131,22 +11131,26 @@ Decl *Sema::ActOnFinishFunctionBody(Decl *dcl, Stmt *Body,
   if (FD) {
     FD->setBody(Body);
 
-    if (getLangOpts().CPlusPlus14 && !FD->isInvalidDecl() && Body &&
-        !FD->isDependentContext() && FD->getReturnType()->isUndeducedType()) {
-      // If the function has a deduced result type but contains no 'return'
-      // statements, the result type as written must be exactly 'auto', and
-      // the deduced result type is 'void'.
-      if (!FD->getReturnType()->getAs<AutoType>()) {
-        Diag(dcl->getLocation(), diag::err_auto_fn_no_return_but_not_auto)
-            << FD->getReturnType();
-        FD->setInvalidDecl();
-      } else {
-        // Substitute 'void' for the 'auto' in the type.
-        TypeLoc ResultType = getReturnTypeLoc(FD);
-        Context.adjustDeducedFunctionResultType(
-            FD, SubstAutoType(ResultType.getType(), Context.VoidTy));
+    if (getLangOpts().CPlusPlus14) {
+      if (!FD->isInvalidDecl() && Body && !FD->isDependentContext() &&
+          FD->getReturnType()->isUndeducedType()) {
+        // If the function has a deduced result type but contains no 'return'
+        // statements, the result type as written must be exactly 'auto', and
+        // the deduced result type is 'void'.
+        if (!FD->getReturnType()->getAs<AutoType>()) {
+          Diag(dcl->getLocation(), diag::err_auto_fn_no_return_but_not_auto)
+              << FD->getReturnType();
+          FD->setInvalidDecl();
+        } else {
+          // Substitute 'void' for the 'auto' in the type.
+          TypeLoc ResultType = getReturnTypeLoc(FD);
+          Context.adjustDeducedFunctionResultType(
+              FD, SubstAutoType(ResultType.getType(), Context.VoidTy));
+        }
       }
     } else if (getLangOpts().CPlusPlus11 && isLambdaCallOperator(FD)) {
+      // In C++11, we don't use 'auto' deduction rules for lambda call
+      // operators because we don't support return type deduction.
       auto *LSI = getCurLambda();
       if (LSI->HasImplicitReturnType) {
         deduceClosureReturnType(*LSI);
diff --git a/lib/Sema/SemaLambda.cpp b/lib/Sema/SemaLambda.cpp
index 884add26e4..1a62f0dfcb 100644
--- a/lib/Sema/SemaLambda.cpp
+++ b/lib/Sema/SemaLambda.cpp
@@ -617,6 +617,8 @@ void Sema::deduceClosureReturnType(CapturingScopeInfo &CSI) {
   assert(CSI.HasImplicitReturnType);
   // If it was ever a placeholder, it had to been deduced to DependentTy.
   assert(CSI.ReturnType.isNull() || !CSI.ReturnType->isUndeducedType()); 
+  assert((!isa<LambdaScopeInfo>(CSI) || !getLangOpts().CPlusPlus14) &&
+         "lambda expressions use auto deduction in C++14 onwards");
 
   // C++ core issue 975:
   //   If a lambda-expression does not include a trailing-return-type,
diff --git a/test/SemaCXX/cxx1y-deduced-return-type.cpp b/test/SemaCXX/cxx1y-deduced-return-type.cpp
index 225d2348cc..e3f6f96801 100644
--- a/test/SemaCXX/cxx1y-deduced-return-type.cpp
+++ b/test/SemaCXX/cxx1y-deduced-return-type.cpp
@@ -496,3 +496,9 @@ namespace TrailingReturnTypeForConversionOperator {
     }
   };
 };
+
+namespace PR24989 {
+  auto x = [](auto){};
+  using T = decltype(x);
+  void (T::*p)(int) const = &T::operator();
+}