Add qt5 main executor and fix stlabConfig.cmake defects (#524)

Support was added for a qt5 main executor since some users need more time to upgrade to qt6 and the complexity increase isn't high.

`stlabConfig.cmake` did not conditionally import dependencies when required by a build configuration. This was fixed as part of this work.

CMakeLists.txt

@@ -9,8 +9,10 @@ include( StlabUtil )
 
 find_package( Boost 1.74.0 OPTIONAL_COMPONENTS unit_test_framework )
 find_package( libdispatch )
+find_package( Qt5 QUIET COMPONENTS Core )
+find_package( Qt6 QUIET COMPONENTS Core )
 find_package( Threads )
-find_package( Qt6 COMPONENTS Core )
+
 
 cmake_dependent_option( stlab.coverage
   "Enable binary instrumentation to collect test coverage information in the DEBUG configuration"
@@ -27,7 +29,7 @@ stlab_detect_task_system(STLAB_DEFAULT_TASK_SYSTEM)
 set(STLAB_TASK_SYSTEM ${STLAB_DEFAULT_TASK_SYSTEM} CACHE STRING "Task system to use (portable|libdispatch|windows).")
 
 stlab_detect_main_executor(STLAB_DEFAULT_MAIN_EXECUTOR)
-set(STLAB_MAIN_EXECUTOR ${STLAB_DEFAULT_MAIN_EXECUTOR} CACHE STRING "Main executor to use (qt|libdispatch|emscripten|none).")
+set(STLAB_MAIN_EXECUTOR ${STLAB_DEFAULT_MAIN_EXECUTOR} CACHE STRING "Main executor to use (qt5|qt6|libdispatch|emscripten|none).")
 
 if( BUILD_TESTING AND NOT Boost_unit_test_framework_FOUND )
   message( SEND_ERROR "BUILD_TESTING is enabled, but an installation of Boost.Test was not found." )
@@ -49,8 +51,12 @@ if( (STLAB_MAIN_EXECUTOR STREQUAL "libdispatch") AND NOT libdispatch_FOUND )
   message( SEND_ERROR "STLAB_MAIN_EXECUTOR is set to \"libdispatch\", but a libdispatch installation was not found." )
 endif()
 
-if( (STLAB_MAIN_EXECUTOR STREQUAL "qt") AND NOT Qt6Core_FOUND )
-  message( SEND_ERROR "STLAB_MAIN_EXECUTOR is set to \"qt\", but a Qt6 installation was not found." )
+if( (STLAB_MAIN_EXECUTOR STREQUAL "qt5") AND NOT Qt5Core_FOUND )
+  message( SEND_ERROR "STLAB_MAIN_EXECUTOR is set to \"qt5\", but a Qt5 installation was not found." )
+endif()
+
+if( (STLAB_MAIN_EXECUTOR STREQUAL "qt6") AND NOT Qt6Core_FOUND )
+  message( SEND_ERROR "STLAB_MAIN_EXECUTOR is set to \"qt6\", but a Qt6 installation was not found." )
 endif()
 
 #
@@ -97,7 +103,9 @@ endif()
 
 if (STLAB_MAIN_EXECUTOR STREQUAL "libdispatch")
   target_link_libraries(stlab INTERFACE libdispatch::libdispatch)
-elseif (STLAB_MAIN_EXECUTOR STREQUAL "qt")
+elseif (STLAB_MAIN_EXECUTOR STREQUAL "qt5")
+  target_link_libraries( stlab INTERFACE Qt5::Core )
+elseif (STLAB_MAIN_EXECUTOR STREQUAL "qt6")
   target_link_libraries( stlab INTERFACE Qt6::Core )
 endif()
 
@@ -185,8 +193,12 @@ install( EXPORT stlabTargets
 # `$INSTALL_DIR/${CMAKE_INSTALL_PREFIX}` is an element of the
 # `CMAKE_PREFIX_PATH` environment variable.
 #
+configure_file(
+  "${stlab_SOURCE_DIR}/cmake/stlabConfig.cmake.in"
+  "${stlab_BINARY_DIR}/stlabConfig.cmake"
+  @ONLY )
 install( FILES
-  "${stlab_SOURCE_DIR}/cmake/stlabConfig.cmake"
+  "${stlab_BINARY_DIR}/stlabConfig.cmake"
   "${stlab_BINARY_DIR}/stlabConfigVersion.cmake"
   DESTINATION share/cmake/stlab )
 

cmake/StlabUtil.cmake

@@ -146,18 +146,20 @@ endfunction()
 # |--------------+--------------------------------------------|
 # | libdispatch  | libdispatch (aka. Grand Central Dispatch ) |
 # | emscripten   | Emscripten's executor                      |
-# | qt           | Qt's event framework                       |
+# | qt5          | Qt's event framework (Qt5)                 |
+# | qt6          | Qt's event framework (Qt6)                 |
 # | none         | None                                       |
 function( stlab_detect_main_executor result_var )
-  find_package(Qt6 QUIET COMPONENTS Core)
   stlab_detect_task_system( task_system )
 
   if( task_system STREQUAL "libdispatch" )
     set( result "libdispatch")
   elseif( CMAKE_SYSTEM_NAME STREQUAL "Emscripten" )
     set( result "emscripten")
   elseif( Qt6Core_FOUND )
-    set( result "qt")
+    set( result "qt6")
+  elseif( Qt5Core_FOUND )
+    set( result "qt5")
   else()
     set( result "none")
   endif()
@@ -194,8 +196,10 @@ function( stlab_generate_config_file )
     set( STLAB_MAIN_EXECUTOR_LIBDISPATCH TRUE )
   elseif (STLAB_MAIN_EXECUTOR STREQUAL "emscripten")
     set( STLAB_MAIN_EXECUTOR_EMSCRIPTEN TRUE )
-  elseif (STLAB_MAIN_EXECUTOR STREQUAL "qt")
-    set( STLAB_MAIN_EXECUTOR_QT TRUE )
+  elseif (STLAB_MAIN_EXECUTOR STREQUAL "qt5")
+    set( STLAB_MAIN_EXECUTOR_QT5 TRUE )
+  elseif (STLAB_MAIN_EXECUTOR STREQUAL "qt6")
+    set( STLAB_MAIN_EXECUTOR_QT6 TRUE )
   elseif (STLAB_MAIN_EXECUTOR STREQUAL "none")
     set( STLAB_MAIN_EXECUTOR_NONE TRUE )
   endif()

cmake/stlabConfig.cmake.in

@@ -0,0 +1,21 @@
+include( CMakeFindDependencyMacro )
+
+if ( @STLAB_USE_BOOST_CPP17_SHIMS@ )
+  find_dependency( Boost 1.74.0 )
+endif()
+
+if ( @STLAB_TASK_SYSTEM@ STREQUAL "libdispatch" )
+  find_dependency( libdispatch )
+endif()
+
+if ( @STLAB_MAIN_EXECUTOR@ STREQUAL "qt5" )
+  find_dependency( Qt5 COMPONENTS Core )
+elseif ( @STLAB_MAIN_EXECUTOR@ STREQUAL "qt6" )
+  find_dependency( Qt6 COMPONENTS Core )
+endif()
+
+if ( NOT @STLAB_THREAD_SYSTEM@ STREQUAL "none" )
+  find_dependency( Threads )
+endif()
+
+include( "${CMAKE_CURRENT_LIST_DIR}/stlabTargets.cmake" )

docs/libraries/concurrency/executor/main_executor/index.md

@@ -13,7 +13,7 @@ description: |
     All tasks that are passed to an instance of this instance are executed in-order on the application's main loop.
 
     Upon destruction of the main_executor, the underlying main loop is _not_ destroyed. Likewise, all functions submitted to the executor will be executed regardless of destruction state.
-    So far no main_executor is implemented for Windows. If QT_CORE_LIB is defined and not STLAB_DISABLE_QT_MAIN_EXECUTOR, a main executor is instantiated that executes the tasks on the Qt main loop.
+    So far no main_executor is implemented for Windows. If STLAB_MAIN_EXECUTOR is qt5 or qt6, a main executor is instantiated that executes the tasks on the Qt main loop.
 member-types:
   - type: result_type
     definition: void

docs/libraries/concurrency/main_executor.hpp/main_executor_type/index.md

@@ -23,4 +23,4 @@ All tasks that are passed to an instance of this instance are executed in-order
 
 Upon destruction of the main_executor, the underlying main loop is _not_ destroyed. Likewise, all functions submitted to the executor will be executed regardless of destruction state.
 
-So far no main_executor is implemented for Windows. If `QT_CORE_LIB` is defined and not `STLAB_DISABLE_QT_MAIN_EXECUTOR`, a main executor is instantiated that executes the tasks on the Qt main loop.
+So far no main_executor is implemented for Windows. If `STLAB_MAIN_EXECUTOR` is `qt5` or `qt6`, a main executor is instantiated that executes the tasks on the Qt main loop.

stlab/concurrency/main_executor.hpp

@@ -13,7 +13,12 @@
 
 #include <stlab/config.hpp>
 
-#if STLAB_MAIN_EXECUTOR(QT)
+#if STLAB_MAIN_EXECUTOR(QT5) || STLAB_MAIN_EXECUTOR(QT6)
+#include <QtGlobal>
+#if (STLAB_MAIN_EXECUTOR(QT5) && (QT_VERSION < QT_VERSION_CHECK(5,0,0) || QT_VERSION >= QT_VERSION_CHECK(6,0,0)) || \
+     STLAB_MAIN_EXECUTOR(QT6) && (QT_VERSION < QT_VERSION_CHECK(6,0,0) || QT_VERSION >= QT_VERSION_CHECK(7,0,0)))
+#error "Mismatching Qt versions"
+#endif
 #include <QCoreApplication>
 #include <QEvent>
 #include <stlab/concurrency/task.hpp>
@@ -38,7 +43,7 @@ namespace detail {
 
 /**************************************************************************************************/
 
-#if STLAB_MAIN_EXECUTOR(QT)
+#if STLAB_MAIN_EXECUTOR(QT5) || STLAB_MAIN_EXECUTOR(QT6)
 
 class main_executor_type {
     using result_type = void;

stlab/config.hpp.in

@@ -28,7 +28,8 @@
 #define STLAB_MAIN_EXECUTOR(X) (STLAB_MAIN_EXECUTOR_##X())
 #cmakedefine01 STLAB_MAIN_EXECUTOR_LIBDISPATCH()
 #cmakedefine01 STLAB_MAIN_EXECUTOR_EMSCRIPTEN()
-#cmakedefine01 STLAB_MAIN_EXECUTOR_QT()
+#cmakedefine01 STLAB_MAIN_EXECUTOR_QT5()
+#cmakedefine01 STLAB_MAIN_EXECUTOR_QT6()
 #cmakedefine01 STLAB_MAIN_EXECUTOR_NONE()
 
 // Various functionality macros