Add support for building against Qt6

- Update CMakeLists.txt to try to load Qt6 and fallback to Qt5 if this
  is not possible
- Update C++ standard requirement to C++17 since Qt6 requires a C++17
  compiler now
- Replace removed `QRegExp` with `QRegularExpression`
- Replace `QString::SkipEmptyParts` with `Qt::SkipEmptyParts` for Qt>=6
  (in order to support all Qt5 versions we still have to use
  `QString::SkipEmptyParts` since `Qt::SkipEmptyParts` was first
  introduced with Qt 5.14)

Author: FMeinicke

CMakeLists.txt

@@ -24,19 +24,19 @@ project(StyleSheets CXX)
 set(StyleSheets_VERSION_MAJOR 0)
 set(StyleSheets_VERSION_MINOR 1)
 
-# Enable C++11
+# Enable C++17
 include(CheckCXXCompilerFlag)
 if(MSVC)
   # Check if we are using Visual Studio 2015 or later
   if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 14)
     message(FATAL_ERROR "You are using an unsupported Windows compiler! (Visual C++ 2015 or later required)")
   endif()
 else()
-  set(cxx11_options -std=c++11)
-  CHECK_CXX_COMPILER_FLAG(${cxx11_options} COMPILER_SUPPORTS_CXX11)
+  set(cxx17_options -std=c++17)
+  CHECK_CXX_COMPILER_FLAG(${cxx17_options} COMPILER_SUPPORTS_CXX17)
 
-  if(NOT COMPILER_SUPPORTS_CXX11)
-    message(FATAL_ERROR "The compiler ${CMAKE_CXX_COMPILER} has insufficient C++11 support. Please use a different C++ compiler.")
+  if(NOT COMPILER_SUPPORTS_CXX17)
+    message(FATAL_ERROR "The compiler ${CMAKE_CXX_COMPILER} has insufficient C++17 support. Please use a different C++ compiler.")
   endif()
 endif()
 
@@ -82,10 +82,8 @@ set(PLUGIN_INSTALL_DIR "${PROJECT_BINARY_DIR}/lib/qml")
 
 enable_testing()
 
-find_package(Qt5Quick 5.3.0 REQUIRED)
-find_package(Qt5Qml 5.3.0 REQUIRED)
-find_package(Qt5Test 5.3.0 REQUIRED)
-find_package(Qt5QuickTest 5.3.0 REQUIRED)
+find_package(QT NAMES Qt6 Qt5 COMPONENTS Quick Qml Test QuickTest REQUIRED)
+find_package(Qt${QT_VERSION_MAJOR} COMPONENTS Quick Qml Test QuickTest REQUIRED)
 
 if(DEFINED Boost_INCLUDE_DIR)
   get_filename_component(Boost_INCLUDE_DIR ${Boost_INCLUDE_DIR} ABSOLUTE)

src/CMakeLists.txt

@@ -42,9 +42,9 @@ add_library(StyleSheetParser
 target_include_directories(StyleSheetParser PUBLIC
   "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include;${PROJECT_SOURCE_DIR}/third-party;${Boost_INCLUDE_DIRS}>")
 target_compile_options(StyleSheetParser
-  PUBLIC ${cxx11_options} ${warning_options})
+  PUBLIC ${cxx17_options} ${warning_options})
 
-target_link_libraries(StyleSheetParser Qt5::Quick)
+target_link_libraries(StyleSheetParser Qt${QT_VERSION_MAJOR}::Quick)
 
 add_library(StylePlugin MODULE
   StyleChecker.cpp
@@ -63,7 +63,7 @@ add_library(StylePlugin MODULE
   StylesDirWatcher.cpp
   StylesDirWatcher.hpp
 )
-target_link_libraries(StylePlugin StyleSheetParser Qt5::Quick)
+target_link_libraries(StylePlugin StyleSheetParser Qt${QT_VERSION_MAJOR}::Quick)
 
 if(WIN32)
   set_target_properties(StylePlugin PROPERTIES PREFIX "")

src/Convert.cpp

@@ -25,6 +25,7 @@ THE SOFTWARE.
 #include "Warnings.hpp"
 
 SUPPRESS_WARNINGS
+#include <QtCore/QRegularExpression>
 #include <QtGui/QColor>
 #include <QtGui/QFont>
 #include <boost/algorithm/clamp.hpp>
@@ -148,10 +149,10 @@ FontSize takeFontSizeFromTokenList(QStringList& tokens)
   if (!tokens.isEmpty()) {
     const QString sizeStr = tokens.takeFirst();
 
-    if (sizeStr.contains(QRegExp("^\\d+px$"))) {
-      fontSize.pixelSize = sizeStr.split(QRegExp("px")).at(0).toInt();
-    } else if (sizeStr.contains(QRegExp("^\\d+(\\.\\d+)?pt$"))) {
-      fontSize.pointSize = sizeStr.split(QRegExp("pt")).at(0).toDouble();
+    if (sizeStr.contains(QRegularExpression("^\\d+px$"))) {
+      fontSize.pixelSize = sizeStr.split(QRegularExpression("px")).at(0).toInt();
+    } else if (sizeStr.contains(QRegularExpression("^\\d+(\\.\\d+)?pt$"))) {
+      fontSize.pointSize = sizeStr.split(QRegularExpression("pt")).at(0).toDouble();
     } else {
       tokens.prepend(sizeStr);
     }
@@ -173,7 +174,11 @@ font: "italic smallcaps bold 16px Times New Roman"
 */
 QFont fontDeclarationToFont(const QString& fontDecl)
 {
-  QStringList tokens = fontDecl.split(QRegExp("\\s* \\s*"), QString::SkipEmptyParts);
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
+  QStringList tokens = fontDecl.split(QRegularExpression("\\s* \\s*"), QString::SkipEmptyParts);
+#else
+  QStringList tokens = fontDecl.split(QRegularExpression("\\s* \\s*"), Qt::SkipEmptyParts);
+#endif
 
   const QFont::Style fontStyle = takeFontStyleFromTokenList(tokens);
   const QFont::Capitalization capMode = takeCapitalizationStyleFromTokenList(tokens);

src/StyleSet.cpp

@@ -72,7 +72,11 @@ std::vector<std::string> styleClassName(QObject* pObj)
   std::vector<std::string> classNames;
 
   if (pStyleSet) {
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     for (auto className : pStyleSet->name().split(" ", QString::SkipEmptyParts)) {
+#else
+    for (auto className : pStyleSet->name().split(" ", Qt::SkipEmptyParts)) {
+#endif
       classNames.emplace_back(className.toStdString());
     }
   }

tests/CMakeLists.txt

@@ -30,9 +30,12 @@ add_library(AqtTestUtilsPlugin MODULE
   TestUtils.cpp
 )
 target_compile_options(AqtTestUtilsPlugin
-  PUBLIC ${cxx11_options} ${warning_options})
+  PUBLIC ${cxx17_options} ${warning_options})
 target_link_libraries(AqtTestUtilsPlugin
-  Qt5::Qml Qt5::Test Qt5::QuickTest)
+  Qt${QT_VERSION_MAJOR}::Qml
+  Qt${QT_VERSION_MAJOR}::Test
+  Qt${QT_VERSION_MAJOR}::QuickTest
+)
 
 if(WIN32)
   set_target_properties(StylePlugin PROPERTIES PREFIX "")

tests/TestUtils.hpp

@@ -59,9 +59,11 @@ class MsgTracker : public QObject
   {
     if (pattern.userType() == QMetaType::QRegularExpression) {
       QTest::ignoreMessage(QtMsgType(level), pattern.toRegularExpression());
+#if QT_VERSION < QT_VERSION_CHECK(6, 0, 0)
     } else if (pattern.userType() == QMetaType::QRegExp) {
       QTest::ignoreMessage(
         QtMsgType(level), QRegularExpression(pattern.toRegExp().pattern()));
+#endif
     } else {
       QTest::ignoreMessage(QtMsgType(level), pattern.toString().toUtf8().data());
     }