build(Linux): harden Qt6 dependency detection

cmake/dependencies/common.cmake

@@ -56,6 +56,17 @@ if(SUNSHINE_ENABLE_TRAY)
 
     add_subdirectory("${CMAKE_SOURCE_DIR}/third-party/tray")
 
+    # TRAY_QT_VERSION is scoped to the tray subdirectory, so inspect the target's actual dependencies.
+    get_target_property(_sunshine_tray_link_libraries tray LINK_LIBRARIES)
+    if("Qt6::Widgets" IN_LIST _sunshine_tray_link_libraries)
+        set(SUNSHINE_TRAY_QT_VERSION 6)
+    elseif("Qt5::Widgets" IN_LIST _sunshine_tray_link_libraries)
+        set(SUNSHINE_TRAY_QT_VERSION 5)
+    else()
+        message(FATAL_ERROR "Could not determine the Qt version used by the tray target.")
+    endif()
+    unset(_sunshine_tray_link_libraries)
+
     if(BUILD_TESTS)
         target_compile_definitions(tray PRIVATE TRAY_ENABLE_TEST_HOOKS)
     endif()

cmake/packaging/linux.cmake

@@ -163,7 +163,7 @@ if(${SUNSHINE_TRAY} STREQUAL 1)
     # Icons used by the Qt tray backend are no longer installed to the hicolor icon theme,
     # because Qt6 will not allow icons not part of the theme... so we will use icons from our web directory instead
 
-    if(TRAY_QT_VERSION EQUAL 6)
+    if(SUNSHINE_TRAY_QT_VERSION EQUAL 6)
         set(CPACK_DEBIAN_PACKAGE_DEPENDS "\
                     ${CPACK_DEBIAN_PACKAGE_DEPENDS}, \
                     libqt6widgets6, \
@@ -178,7 +178,7 @@ if(${SUNSHINE_TRAY} STREQUAL 1)
                 devel/qt6-base
                 graphics/qt6-svg
         )
-    else()
+    elseif(SUNSHINE_TRAY_QT_VERSION EQUAL 5)
         set(CPACK_DEBIAN_PACKAGE_DEPENDS "\
                     ${CPACK_DEBIAN_PACKAGE_DEPENDS}, \
                     libqt5widgets5, \
@@ -193,6 +193,8 @@ if(${SUNSHINE_TRAY} STREQUAL 1)
                 x11-toolkits/qt5-widgets
                 graphics/qt5-svg
         )
+    else()
+        message(FATAL_ERROR "Unsupported tray Qt version: ${SUNSHINE_TRAY_QT_VERSION}")
     endif()
 endif()
 

docker/debian.dockerfile

@@ -78,6 +78,17 @@ set -e
 ./scripts/linux_build.sh \
   --step=package \
   --sudo-off
+
+package_dependencies="$(dpkg-deb --field build/cpack_artifacts/*.deb Depends)"
+package_dependencies_valid=false
+case "${package_dependencies}" in
+  *libqt5*) ;;
+  *libqt6widgets6*libqt6svg6* | *libqt6svg6*libqt6widgets6*) package_dependencies_valid=true ;;
+esac
+if [ "${package_dependencies_valid}" = false ]; then
+  echo "Unexpected Qt package dependencies: ${package_dependencies}"
+  exit 1
+fi
 _BUILD
 
 # run tests

docs/getting_started.md

@@ -202,7 +202,7 @@ sudo apt install sunshine
 
 Download `sunshine_{version}-1+{distro}{distro-version}_{arch}.deb` and run the following command.
 ```bash
-sudo dpkg -i ./sunshine_{version}-1+{distro}{distro-version}_{arch}.deb
+sudo apt install ./sunshine_{version}-1+{distro}{distro-version}_{arch}.deb
 ```
 
 > [!NOTE]