From: Erich Keane <erich.keane@intel.com>
Date: Wed, 19 Apr 2017 21:24:55 +0000 (+0000)
Subject: Corrrect warn_unused_result attribute
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=50cdd18bb1c87febc93cd84eaa1bafd74d9d1c16;p=clang

Corrrect warn_unused_result attribute

The original idea was that if the attribute on an operator,
that the return-value unused-ness wouldn't matter. However,
all of the operators except postfix inc/dec return
references! References don't result in this warning
anyway, so those are already excluded.

Differential Revision: https://reviews.llvm.org/D32207


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@300764 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/include/clang/AST/Decl.h b/include/clang/AST/Decl.h
index ad723a3e2b..573ea55de1 100644
--- a/include/clang/AST/Decl.h
+++ b/include/clang/AST/Decl.h
@@ -2082,10 +2082,7 @@ public:
   const Attr *getUnusedResultAttr() const;
 
   /// \brief Returns true if this function or its return type has the
-  /// warn_unused_result attribute. If the return type has the attribute and
-  /// this function is a method of the return type's class, then false will be
-  /// returned to avoid spurious warnings on member methods such as assignment
-  /// operators.
+  /// warn_unused_result attribute.
   bool hasUnusedResultAttr() const { return getUnusedResultAttr() != nullptr; }
 
   /// \brief Returns the storage class as written in the source. For the
diff --git a/lib/AST/Decl.cpp b/lib/AST/Decl.cpp
index 2b22e5bb50..094e8dcff0 100644
--- a/lib/AST/Decl.cpp
+++ b/lib/AST/Decl.cpp
@@ -3003,9 +3003,7 @@ SourceRange FunctionDecl::getExceptionSpecSourceRange() const {
 const Attr *FunctionDecl::getUnusedResultAttr() const {
   QualType RetType = getReturnType();
   if (RetType->isRecordType()) {
-    const CXXRecordDecl *Ret = RetType->getAsCXXRecordDecl();
-    const auto *MD = dyn_cast<CXXMethodDecl>(this);
-    if (Ret && !(MD && MD->getCorrespondingMethodInClass(Ret, true))) {
+    if (const CXXRecordDecl *Ret = RetType->getAsCXXRecordDecl()) {
       if (const auto *R = Ret->getAttr<WarnUnusedResultAttr>())
         return R;
     }
diff --git a/test/SemaCXX/warn-unused-result.cpp b/test/SemaCXX/warn-unused-result.cpp
index 01bc457ec2..88f5ab1e85 100644
--- a/test/SemaCXX/warn-unused-result.cpp
+++ b/test/SemaCXX/warn-unused-result.cpp
@@ -160,3 +160,49 @@ void g() {
   (void)noexcept(f(), false); // Should not warn.
 }
 }
+
+namespace {
+// C++ Methods should warn even in their own class.
+struct [[clang::warn_unused_result]] S {
+  S DoThing() { return {}; };
+  S operator++(int) { return {}; };
+  S operator--(int) { return {}; };
+  // Improperly written prefix.
+  S operator++() { return {}; };
+  S operator--() { return {}; };
+};
+
+struct [[clang::warn_unused_result]] P {
+  P DoThing() { return {}; };
+};
+
+P operator++(const P &, int) { return {}; };
+P operator--(const P &, int) { return {}; };
+// Improperly written prefix.
+P operator++(const P &) { return {}; };
+P operator--(const P &) { return {}; };
+
+void f() {
+  S s;
+  P p;
+  s.DoThing(); // expected-warning {{ignoring return value}}
+  p.DoThing(); // expected-warning {{ignoring return value}}
+  // Only postfix is expected to warn when written correctly.
+  s++; // expected-warning {{ignoring return value}}
+  s--; // expected-warning {{ignoring return value}}
+  p++; // expected-warning {{ignoring return value}}
+  p--; // expected-warning {{ignoring return value}}
+  // Improperly written prefix operators should still warn.
+  ++s; // expected-warning {{ignoring return value}}
+  --s; // expected-warning {{ignoring return value}}
+  ++p; // expected-warning {{ignoring return value}}
+  --p; // expected-warning {{ignoring return value}}
+
+  // Silencing the warning by cast to void still works.
+  (void)s.DoThing();
+  (void)s++;
+  (void)p++;
+  (void)++s;
+  (void)++p;
+}
+} // namespace