From d254d8c19714af69a9897bdd67c4e9aa3267c3a3 Mon Sep 17 00:00:00 2001
From: Thiago Macieira <thiago.macieira@intel.com>
Date: Tue, 18 Apr 2017 16:43:41 -0700
Subject: Use the C++ [[nodiscard]] attribute

Change-Id: I7814054a102a407d876ffffd14b6a285c70b21de
Reviewed-by: Olivier Goffart (Woboq GmbH) <ogoffart@woboq.com>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
---
 src/corelib/global/qcompilerdetection.h | 67 ++++++++++++++++++---------------
 src/corelib/tools/qbytearray.h          |  2 +-
 src/corelib/tools/qstring.h             |  2 +-
 3 files changed, 38 insertions(+), 33 deletions(-)

(limited to 'src/corelib')

diff --git a/src/corelib/global/qcompilerdetection.h b/src/corelib/global/qcompilerdetection.h
index c221115e8f..9ffd164b61 100644
--- a/src/corelib/global/qcompilerdetection.h
+++ b/src/corelib/global/qcompilerdetection.h
@@ -1060,6 +1060,37 @@
 # endif
 #endif
 
+/*
+ * SG10's SD-6 feature detection and some useful extensions from Clang and GCC
+ * https://isocpp.org/std/standing-documents/sd-6-sg10-feature-test-recommendations
+ * http://clang.llvm.org/docs/LanguageExtensions.html#feature-checking-macros
+ */
+#ifdef __has_builtin
+#  define QT_HAS_BUILTIN(x)             __has_builtin(x)
+#else
+#  define QT_HAS_BUILTIN(x)             0
+#endif
+#ifdef __has_attribute
+#  define QT_HAS_ATTRIBUTE(x)           __has_attribute(x)
+#else
+#  define QT_HAS_ATTRIBUTE(x)           0
+#endif
+#ifdef __has_cpp_attribute
+#  define QT_HAS_CPP_ATTRIBUTE(x)       __has_cpp_attribute(x)
+#else
+#  define QT_HAS_CPP_ATTRIBUTE(x)       0
+#endif
+#ifdef __has_include
+#  define QT_HAS_INCLUDE(x)             __has_include(x)
+#else
+#  define QT_HAS_INCLUDE(x)             0
+#endif
+#ifdef __has_include_next
+#  define QT_HAS_INCLUDE_NEXT(x)        __has_include_next(x)
+#else
+#  define QT_HAS_INCLUDE_NEXT(x)        0
+#endif
+
 /*
  * C++11 keywords and expressions
  */
@@ -1141,6 +1172,11 @@
 #  define Q_DECL_ALIGN(n)   alignas(n)
 #endif
 
+#if QT_HAS_CPP_ATTRIBUTE(nodiscard)         // P0188R1
+#  undef Q_REQUIRED_RESULT
+#  define Q_REQUIRED_RESULT [[nodiscard]]
+#endif
+
 /*
  * Fallback macros to certain compiler features
  */
@@ -1215,37 +1251,6 @@
 #ifndef QT_MAKE_CHECKED_ARRAY_ITERATOR
 #  define QT_MAKE_CHECKED_ARRAY_ITERATOR(x, N) (x)
 #endif
-
-/*
- * SG10's SD-6 feature detection and some useful extensions from Clang and GCC
- * https://isocpp.org/std/standing-documents/sd-6-sg10-feature-test-recommendations
- * http://clang.llvm.org/docs/LanguageExtensions.html#feature-checking-macros
- */
-#ifdef __has_builtin
-#  define QT_HAS_BUILTIN(x)             __has_builtin(x)
-#else
-#  define QT_HAS_BUILTIN(x)             0
-#endif
-#ifdef __has_attribute
-#  define QT_HAS_ATTRIBUTE(x)           __has_attribute(x)
-#else
-#  define QT_HAS_ATTRIBUTE(x)           0
-#endif
-#ifdef __has_cpp_attribute
-#  define QT_HAS_CPP_ATTRIBUTE(x)       __has_cpp_attribute(x)
-#else
-#  define QT_HAS_CPP_ATTRIBUTE(x)       0
-#endif
-#ifdef __has_include
-#  define QT_HAS_INCLUDE(x)             __has_include(x)
-#else
-#  define QT_HAS_INCLUDE(x)             0
-#endif
-#ifdef __has_include_next
-#  define QT_HAS_INCLUDE_NEXT(x)        __has_include_next(x)
-#else
-#  define QT_HAS_INCLUDE_NEXT(x)        0
-#endif
 #ifdef __has_feature
 #  define QT_HAS_FEATURE(x)             __has_feature(x)
 #else
diff --git a/src/corelib/tools/qbytearray.h b/src/corelib/tools/qbytearray.h
index 03bb9b5747..432ef922f6 100644
--- a/src/corelib/tools/qbytearray.h
+++ b/src/corelib/tools/qbytearray.h
@@ -243,7 +243,7 @@ public:
     void chop(int n);
 
 #if defined(Q_COMPILER_REF_QUALIFIERS) && !defined(QT_COMPILING_QSTRING_COMPAT_CPP) && !defined(Q_CLANG_QDOC)
-#  if defined(Q_CC_GNU) && !defined(Q_CC_CLANG) && !defined(Q_CC_INTEL)
+#  if defined(Q_CC_GNU) && !defined(Q_CC_CLANG) && !defined(Q_CC_INTEL) && !QT_HAS_CPP_ATTRIBUTE(nodiscard)
     // required due to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61941
 #    pragma push_macro("Q_REQUIRED_RESULT")
 #    undef Q_REQUIRED_RESULT
diff --git a/src/corelib/tools/qstring.h b/src/corelib/tools/qstring.h
index 109b68c544..88ba4a3fb5 100644
--- a/src/corelib/tools/qstring.h
+++ b/src/corelib/tools/qstring.h
@@ -383,7 +383,7 @@ public:
     Q_REQUIRED_RESULT QString rightJustified(int width, QChar fill = QLatin1Char(' '), bool trunc = false) const;
 
 #if defined(Q_COMPILER_REF_QUALIFIERS) && !defined(QT_COMPILING_QSTRING_COMPAT_CPP) && !defined(Q_CLANG_QDOC)
-#  if defined(Q_CC_GNU) && !defined(Q_CC_CLANG) && !defined(Q_CC_INTEL)
+#  if defined(Q_CC_GNU) && !defined(Q_CC_CLANG) && !defined(Q_CC_INTEL) && !QT_HAS_CPP_ATTRIBUTE(nodiscard)
     // required due to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61941
 #    pragma push_macro("Q_REQUIRED_RESULT")
 #    undef Q_REQUIRED_RESULT
-- 
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