Generalize the winmain/qtmain entry-point library

The use-case is relevant for other platforms as well.

Now that Qt has a module system we can also replace a lot of the
hand crafted logic for linking with simpler constructs.

Change-Id: Ib6853aaf81bfea79c31f2de741d65b4b56f23ef6
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>

3 files changed, 165 insertions, 0 deletions

diff --git a/src/entrypoint/CMakeLists.txt b/src/entrypoint/CMakeLists.txt
new file mode 100644
index 0000000000..16c01540dd
--- /dev/null
+++ b/src/entrypoint/CMakeLists.txt
@@ -0,0 +1,33 @@
+# special case begin
+# special case skip regeneration
+if (NOT WIN32)
+    return()
+endif()
+
+qt_internal_add_module(EntryPoint
+  STATIC
+  NO_SYNC_QT
+  NO_MODULE_HEADERS
+  DEFINES
+      QT_NO_FOREACH
+  INCLUDE_DIRECTORIES
+      $<TARGET_PROPERTY:Qt::Core,INTERFACE_INCLUDE_DIRECTORIES>
+)
+
+if (MSVC)
+    # Store debug information inside the static lib
+    qt_internal_replace_compiler_flags(
+        "/Zi" "/Z7"
+        CONFIGS DEBUG RELWITHDEBINFO
+        IN_CURRENT_SCOPE)
+endif()
+
+qt_internal_extend_target(EntryPoint CONDITION WIN32
+    SOURCES qtentrypoint_win.cpp
+    LIBRARIES shell32
+)
+
+qt_internal_extend_target(EntryPoint CONDITION MINGW
+    DEFINES QT_NEEDS_QMAIN
+)
+# special case end
diff --git a/src/entrypoint/entrypoint.pro b/src/entrypoint/entrypoint.pro
new file mode 100644
index 0000000000..dd0618cd56
--- /dev/null
+++ b/src/entrypoint/entrypoint.pro
@@ -0,0 +1,30 @@
+# Additional Qt project file for QtEntryPoint lib
+!win32:error("$$_FILE_ is intended only for Windows!")
+
+TARGET = QtEntryPoint
+
+CONFIG += static no_module_headers
+QT = core
+
+DEFINES += QT_NO_FOREACH
+
+win32 {
+    SOURCES = qtentrypoint_win.cpp
+    CONFIG -= qt
+
+    QMAKE_USE_PRIVATE += shell32
+
+    msvc {
+        QMAKE_CFLAGS_DEBUG -= -Zi
+        QMAKE_CXXFLAGS_DEBUG -= -Zi
+        QMAKE_CFLAGS_DEBUG *= -Z7
+        QMAKE_CXXFLAGS_DEBUG *= -Z7
+    }
+    mingw {
+        DEFINES += QT_NEEDS_QMAIN
+        MODULE_DEFINES += QT_NEEDS_QMAIN
+        LIBS += -lmingw32
+    }
+}
+
+load(qt_module)
diff --git a/src/entrypoint/qtentrypoint_win.cpp b/src/entrypoint/qtentrypoint_win.cpp
new file mode 100644
index 0000000000..200eb5379d
--- /dev/null
+++ b/src/entrypoint/qtentrypoint_win.cpp
@@ -0,0 +1,102 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the Windows main function of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <windows.h>
+#include <shellapi.h>
+
+/*
+  This file contains the code in the QtEntryPoint library for Windows.
+  QtEntryPoint contains the Windows startup code and is required for
+  linking to the Qt DLL.
+
+  When a Windows application starts, the WinMain function is
+  invoked.
+*/
+
+#if defined(QT_NEEDS_QMAIN)
+int qMain(int, char **);
+#define main qMain
+#else
+extern "C" int main(int, char **);
+#endif
+
+/*
+  WinMain() - Initializes Windows and calls user's startup function main().
+  NOTE: WinMain() won't be called if the application was linked as a "console"
+  application.
+*/
+
+// Convert a wchar_t to char string, equivalent to QString::toLocal8Bit()
+// when passed CP_ACP.
+static inline char *wideToMulti(unsigned int codePage, const wchar_t *aw)
+{
+    const int required = WideCharToMultiByte(codePage, 0, aw, -1, nullptr, 0, nullptr, nullptr);
+    char *result = new char[required];
+    WideCharToMultiByte(codePage, 0, aw, -1, result, required, nullptr, nullptr);
+    return result;
+}
+
+extern "C" int APIENTRY WinMain(HINSTANCE, HINSTANCE, LPSTR /*cmdParamarg*/, int /* cmdShow */)
+{
+    int argc = 0;
+    wchar_t **argvW = CommandLineToArgvW(GetCommandLineW(), &argc);
+    if (argvW == nullptr)
+        return -1;
+    char **argv = new char *[argc + 1];
+    for (int i = 0; i != argc; ++i)
+        argv[i] = wideToMulti(CP_ACP, argvW[i]);
+    argv[argc] = nullptr;
+    LocalFree(argvW);
+    const int exitCode = main(argc, argv);
+    for (int i = 0; (i != argc) && (argv[i] != nullptr); ++i)
+        delete [] argv[i];
+    delete [] argv;
+    return exitCode;
+}