[LyX/2.4.x] Cmake build: Make QT5-compilation be default

[Kornel Benko]

commit c971974f331c249fa4d57953d8d93c107c154024
Author: Kornel Benko <kornel at lyx.org>
Date:   Sat Apr 6 12:36:47 2024 +0200

    Cmake build: Make QT5-compilation be default
---
 CMakeLists.txt | 36 ++++++++++++++++++++++--------------
 1 file changed, 22 insertions(+), 14 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0fb6cf284a..363f413153 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -662,23 +662,31 @@ endif()
 
 set(min_qt5_version "5.6")
 if(LYX_USE_QT MATCHES "AUTO")
-	# try qt6 first
-	find_package(Qt6Core CONFIG QUIET)
-	if (Qt6Core_FOUND)
-		set(LYX_USE_QT "QT6" CACHE STRING "Valid qt version" FORCE)
-		message(STATUS "Qt6Core_VERSION = ${Qt6Core_VERSION}")
-	else()
-		find_package(Qt5Core CONFIG QUIET)
-		if(Qt5Core_FOUND)
-			set(LYX_USE_QT "QT5" CACHE STRING "Valid qt version" FORCE)
-			message(STATUS "Qt5Core_VERSION = ${Qt5Core_VERSION}")
-			if(Qt5Core_VERSION VERSION_LESS ${min_qt5_version})
-				message(FATAL_ERROR "No appropriate QT-version found")
-			endif()
+	# try qt5 first
+	find_package(Qt5Core CONFIG QUIET)
+	if(Qt5Core_FOUND)
+		message(STATUS "Qt5Core_VERSION = ${Qt5Core_VERSION}")
+		if(Qt5Core_VERSION VERSION_LESS ${min_qt5_version})
+			message(STATUS "No appropriate QT-version found")
+			set(Qt5Core_FOUND OFF)
 		else()
-			message(FATAL_ERROR "No appropriate QT-version found")
+			set(LYX_USE_QT "QT5" CACHE STRING "Valid qt version" FORCE)
+			set(Qt6Core_FOUND OFF)
 		endif()
 	endif()
+	if (NOT Qt5Core_FOUND)
+		foreach(_mod Core Gui Widgets Concurrent Svg)
+			find_package(Qt6${_mod} CONFIG QUIET)
+			if (NOT Qt6${_mod}_FOUND)
+				message(FATAL_ERROR "Not found Qt6${_mod}, aborting use of QT6")
+				set(Qt6Core_FOUND OFF)
+				break()
+			else()
+				message(STATUS "Found Qt6${_mod}")
+			endif()
+		endforeach()
+		set(LYX_USE_QT "QT6" CACHE STRING "Valid qt version" FORCE)
+	endif()
 endif()
 
 # When shared libs are supported enable this option