Handle a difference in lambda return type deduction between C++11 and C++1y: if

no return type is specified, C++11 will deduce a cv-qualified return type in
some cases, but C++1y never will.

llvm-svn: 187275

3 files changed, 27 insertions, 4 deletions

diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index 7feb96f6a64..61319d22389 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -2376,9 +2376,15 @@ Sema::ActOnCapScopeReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp) {
         return StmtError();
       RetValExp = Result.take();
 
-      if (!CurContext->isDependentContext())
+      if (!CurContext->isDependentContext()) {
         FnRetType = RetValExp->getType();
-      else
+        // In C++11, we take the type of the expression after decay and
+        // lvalue-to-rvalue conversion, so a class type can be cv-qualified.
+        // In C++1y, we perform template argument deduction as if the return
+        // type were 'auto', so an implicit return type is never cv-qualified.
+        if (getLangOpts().CPlusPlus1y && FnRetType.hasQualifiers())
+          FnRetType = FnRetType.getUnqualifiedType();
+      } else
         FnRetType = CurCap->ReturnType = Context.DependentTy;
     } else {
       if (RetValExp) {
diff --git a/clang/test/CXX/expr/expr.prim/expr.prim.lambda/p4.cpp b/clang/test/CXX/expr/expr.prim/expr.prim.lambda/p4.cpp
index 368b3f695b9..c69aa115beb 100644
--- a/clang/test/CXX/expr/expr.prim/expr.prim.lambda/p4.cpp
+++ b/clang/test/CXX/expr/expr.prim/expr.prim.lambda/p4.cpp
@@ -39,7 +39,10 @@ X infer_X_return_type_fail(X x) {
     if (y > 0)
       return X();
     else
-      return x; // expected-error{{return type 'const X' must match previous return type 'X' when lambda expression has unspecified explicit return type}}
+      return x;
+#if __cplusplus <= 201103L
+    // expected-error@-2 {{return type 'const X' must match previous return type 'X' when lambda expression has unspecified explicit return type}}
+#endif
   }(5);
 }
 
diff --git a/clang/test/SemaCXX/lambda-expressions.cpp b/clang/test/SemaCXX/lambda-expressions.cpp
index 8736afe4b0b..e8e2eb612a0 100644
--- a/clang/test/SemaCXX/lambda-expressions.cpp
+++ b/clang/test/SemaCXX/lambda-expressions.cpp
@@ -1,4 +1,5 @@
-// RUN: %clang_cc1 -std=c++0x -Wno-unused-value -fsyntax-only -verify -fblocks %s
+// RUN: %clang_cc1 -std=c++11 -Wno-unused-value -fsyntax-only -verify -fblocks %s
+// RUN: %clang_cc1 -std=c++1y -Wno-unused-value -fsyntax-only -verify -fblocks %s
 
 namespace std { class type_info; };
 
@@ -251,3 +252,16 @@ namespace PR16708 {
     return 0;
   };
 }
+
+namespace TypeDeduction {
+  struct S {};
+  void f() {
+    const S s {};
+    S &&t = [&] { return s; } ();
+#if __cplusplus <= 201103L
+    // expected-error@-2 {{drops qualifiers}}
+#else
+    S &&u = [&] () -> auto { return s; } ();
+#endif
+  }
+}