feat(cmake): Compile translations on during build

Should be quite quick. This allows removing the binary `*.qm` files from
the source tree and thus reduce of both the size of diffs and the
transferred git object deltas on translation changes.

.gitattributes

@@ -19,7 +19,6 @@
 
 # Exclude Transifex files from merging
 /res/translations/*.ts merge=ours
-/res/translations/*.qm merge=ours
 
 # Treat serato test data as binary
 *.octet-stream binary

.gitignore

@@ -66,3 +66,6 @@ src/mixxx.rc.include
 src/mixxx.res
 src/test/**/*.actual
 res/qrc_mixxx.cc
+
+# Ignore translations (now compiled via CMake and removed from git)
+res/translations/*.qm

CMakeLists.txt

@@ -2634,6 +2634,53 @@ elseif(WIN32)
   endif()
 endif()
 
+# Mixxx translation files
+file(GLOB MIXXX_TS_FILES "${CMAKE_CURRENT_SOURCE_DIR}/res/translations/*.ts")
+message(VERBOSE "Mixxx translation files: ${MIXXX_TS_FILES}")
+
+if(QT6 AND FALSE)
+  find_package(Qt${QT_VERSION_MAJOR} REQUIRED COMPONENTS LinguistTools)
+  set_source_files_properties(
+    ${MIXXX_TS_FILES}
+    PROPERTIES OUTPUT_LOCATION "${CMAKE_CURRENT_SOURCE_DIR}/res/translations"
+  )
+  qt_add_lrelease(
+    TS_FILES ${MIXXX_TS_FILES}
+    LRELEASE_TARGET mixxx-translations
+    EXCLUDE_FROM_ALL
+    NO_GLOBAL_TARGET
+    QM_FILES_OUTPUT_VARIABLE MIXXX_TRANSLATIONS
+    OPTIONS -nounfinished
+  )
+else()
+  find_program(LRELEASE_EXECUTABLE "lrelease")
+  if(LRELEASE_EXECUTABLE)
+    message(STATUS "Found lrelease: ${LRELEASE_EXECUTABLE}")
+  else()
+    message(STATUS "Could NOT find lrelease (missing executable)")
+  endif()
+
+  set(MIXXX_QM_FILES "")
+  foreach(TS_FILE ${MIXXX_TS_FILES})
+    string(REGEX REPLACE "[.]ts$" ".qm" QM_FILE "${TS_FILE}")
+    add_custom_command(
+      OUTPUT "${QM_FILE}"
+      DEPENDS "${TS_FILE}"
+      COMMAND "${LRELEASE_EXECUTABLE}" -nounfinished "${TS_FILE}" -qm "${QM_FILE}"
+    )
+    list(APPEND MIXXX_QM_FILES "${QM_FILE}")
+  endforeach()
+  add_custom_target(mixxx-translations DEPENDS ${MIXXX_QM_FILES})
+endif()
+add_dependencies(mixxx mixxx-translations)
+install(
+  FILES
+    ${MIXXX_TRANSLATIONS}
+  DESTINATION
+    "${MIXXX_INSTALL_DATADIR}/translations"
+)
+
+# Qt translation files
 if(APPLE OR WIN32)
   # qt_de.qm is just one arbitrary file in the directory that needs to be located;
   # there is no particular reason to look for this file versus any other one in the directory.