Move detection of <future> to a configure test

<future> is needed by QThread::create. Instead of a fragile series
of preprocessor tests, move its detection to a configure test.
This dramatically simplifies the code, but on the other hand ties
the availability of QThread::create() to the system used to compile
Qt (rather the one used to compile an application).

Change-Id: If1b06363379bf29126cfa68f2a0651cbb78a67f7
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/configure.json

@@ -251,6 +251,18 @@
                 ]
             }
         },
+        "cxx11_future": {
+            "label": "C++11 <future>",
+            "type": "compile",
+            "test": {
+                "include": "future",
+                "main": [
+                    "std::future<int> f = std::async([]() { return 42; });",
+                    "(void)f.get();"
+                ],
+                "qmake": "unix:LIBS += -lpthread"
+            }
+        },
         "cxx11_random": {
             "label": "C++11 <random>",
             "type": "compile",
@@ -442,6 +454,11 @@
             "condition": "features.doubleconversion && libs.doubleconversion",
             "output": [ "privateFeature" ]
         },
+        "cxx11_future": {
+            "label": "C++11 <future>",
+            "condition": "tests.cxx11_future",
+            "output": [ "publicFeature" ]
+        },
         "cxx11_random": {
             "label": "C++11 <random>",
             "condition": "tests.cxx11_random",

src/corelib/thread/qthread.cpp

@@ -925,7 +925,7 @@ bool QThread::isInterruptionRequested() const
     \sa start()
 */
 
-#ifdef QTHREAD_HAS_CREATE
+#if QT_CONFIG(cxx11_future)
 class QThreadCreateThread : public QThread
 {
 public:
@@ -947,7 +947,7 @@ QThread *QThread::createThreadImpl(std::future<void> &&future)
 {
     return new QThreadCreateThread(std::move(future));
 }
-#endif // QTHREAD_HAS_CREATE
+#endif // QT_CONFIG(cxx11_future)
 
 /*!
     \class QDaemonThread

src/corelib/thread/qthread.h

@@ -1,6 +1,7 @@
 /****************************************************************************
 **
 ** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2017 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com, author Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
@@ -42,17 +43,10 @@
 
 #include <QtCore/qobject.h>
 
-// The implementation of QThread::create uses various C++14/C++17 facilities;
-// we must check for their presence. Specifically for glibcxx bundled in MinGW
-// with win32 threads, we check the condition found in its <future> header
-// since _GLIBCXX_HAS_GTHREADS might then not be defined.
-// For std::async (used in all codepaths)
-// there is no SG10 feature macro; just test for the header presence.
-// For the C++17 codepath do some more throughout checks for std::invoke and
-// C++14 lambdas availability.
-#if QT_HAS_INCLUDE(<future>) \
-    && (!defined(__GLIBCXX__) || (defined(_GLIBCXX_HAS_GTHREADS) && defined(_GLIBCXX_USE_C99_STDINT_TR1)))
-#  define QTHREAD_HAS_CREATE
+// For QThread::create. The configure-time test just checks for the availability
+// of std::future and std::async; for the C++17 codepath we perform some extra
+// checks here (for std::invoke and C++14 lambdas).
+#if QT_CONFIG(cxx11_future)
 #  include <future> // for std::async
 #  include <functional> // for std::invoke; no guard needed as it's a C++98 header
 
@@ -125,16 +119,16 @@ public:
     template <typename Function>
     static QThread *create(Function &&f);
 #else
-#ifdef QTHREAD_HAS_CREATE
-#ifdef QTHREAD_HAS_VARIADIC_CREATE
+#  if QT_CONFIG(cxx11_future)
+#    ifdef QTHREAD_HAS_VARIADIC_CREATE
     template <typename Function, typename... Args>
     static QThread *create(Function &&f, Args &&... args);
-#else
+#    else
     template <typename Function>
     static QThread *create(Function &&f);
-#endif
-#endif
-#endif
+#    endif // QTHREAD_HAS_VARIADIC_CREATE
+#  endif // QT_CONFIG(cxx11_future)
+#endif // Q_QDOC
 
 public Q_SLOTS:
     void start(Priority = InheritPriority);
@@ -165,7 +159,7 @@ protected:
 private:
     Q_DECLARE_PRIVATE(QThread)
 
-#ifdef QTHREAD_HAS_CREATE
+#if QT_CONFIG(cxx11_future)
     static QThread *createThreadImpl(std::future<void> &&future);
 #endif
 
@@ -173,9 +167,9 @@ private:
     friend class QThreadData;
 };
 
-#ifdef QTHREAD_HAS_CREATE
+#if QT_CONFIG(cxx11_future)
 
-#ifdef QTHREAD_HAS_VARIADIC_CREATE
+#if defined(QTHREAD_HAS_VARIADIC_CREATE)
 // C++17: std::thread's constructor complying call
 template <typename Function, typename... Args>
 QThread *QThread::create(Function &&f, Args &&... args)
@@ -243,7 +237,7 @@ QThread *QThread::create(Function &&f)
 }
 #endif // QTHREAD_HAS_VARIADIC_CREATE
 
-#endif // QTHREAD_HAS_CREATE
+#endif // QT_CONFIG(cxx11_future)
 
 #else // QT_NO_THREAD
 

tests/auto/corelib/thread/qthread/tst_qthread.cpp

@@ -1338,7 +1338,7 @@ void tst_QThread::quitLock()
 
 void tst_QThread::create()
 {
-#ifndef QTHREAD_HAS_CREATE
+#if !QT_CONFIG(cxx11_future)
     QSKIP("This test requires QThread::create");
 #else
     {
@@ -1586,7 +1586,7 @@ void tst_QThread::create()
     }
 #endif // QT_NO_EXCEPTIONS
 #endif // QTHREAD_HAS_VARIADIC_CREATE
-#endif // QTHREAD_HAS_CREATE
+#endif // QT_CONFIG(cxx11_future)
 }
 
 class StopableJob : public QObject