CMake: Change behavior of automatic determination of .ts files

...according to the Qt 6.7 CMake i18n API review.

Add the NO_GENERATE_PLURALS_TS_FILE option to qt_add_translations and
don't generate a plurals .ts file if QT_I18N_SOURCE_LANGUAGE is in
QT_I18N_TRANSLATED_LANGUAGES.

Task-number: QTBUG-122396
Change-Id: I82e1828b8ce7367ba7f15b9cb1f6341441d806f3
Reviewed-by:  Alexey Edelev <alexey.edelev@qt.io>
(cherry picked from commit 908404d9f97880dd89905d37a3964c3d4a3337be)
Reviewed-by:  Alexey Edelev <alexey.edelev@qt.io>

3 files changed, 71 insertions, 21 deletions

diff --git a/src/linguist/Qt6LinguistToolsMacros.cmake b/src/linguist/Qt6LinguistToolsMacros.cmake
index 555b18d21..7cf6d89a9 100644
--- a/src/linguist/Qt6LinguistToolsMacros.cmake
+++ b/src/linguist/Qt6LinguistToolsMacros.cmake
@@ -535,7 +535,8 @@ endfunction()
 
 function(qt6_add_translations)
     set(options
-        IMMEDIATE_CALL)
+        IMMEDIATE_CALL
+        NO_GENERATE_PLURALS_TS_FILE)
     set(oneValueArgs
         LUPDATE_TARGET
         LRELEASE_TARGET
@@ -565,14 +566,6 @@ function(qt6_add_translations)
     if(targets STREQUAL "")
         message(FATAL_ERROR "No targets provided.")
     endif()
-    if(NOT DEFINED arg_TS_FILES
-            AND NOT DEFINED arg_PLURALS_TS_FILE
-            AND "${QT_I18N_TRANSLATED_LANGUAGES}" STREQUAL ""
-            AND "${QT_I18N_SOURCE_LANGUAGE}" STREQUAL "")
-        message(FATAL_ERROR
-            "One of QT_I18N_TRANSLATED_LANGUAGES, QT_I18N_SOURCE_LANGUAGE, TS_FILES, "
-            "or PLURALS_TS_FILE must be provided.")
-    endif()
     if(DEFINED arg_RESOURCE_PREFIX AND DEFINED arg_QM_FILES_OUTPUT_VARIABLE)
         message(FATAL_ERROR "QM_FILES_OUTPUT_VARIABLE cannot be specified "
             "together with RESOURCE_PREFIX.")
@@ -599,10 +592,19 @@ function(qt6_add_translations)
             list(APPEND arg_TS_FILES "${arg_TS_FILE_DIR}/${arg_TS_FILE_BASE}_${lang}.ts")
         endforeach()
 
-        # Determine the path to the native .ts file if necessary.
-        if(NOT DEFINED arg_PLURALS_TS_FILE AND NOT "${QT_I18N_SOURCE_LANGUAGE}" STREQUAL "")
+        # Default the source language to "en" in case the user doesn't use
+        # qt_standard_project_setup.
+        set(source_lang en)
+        if(NOT "${QT_I18N_SOURCE_LANGUAGE}" STREQUAL "")
+            set(source_lang ${QT_I18N_SOURCE_LANGUAGE})
+        endif()
+
+        # Determine the path to the plurals-only .ts file if necessary.
+        if(NOT arg_NO_GENERATE_PLURALS_TS_FILE
+            AND NOT DEFINED arg_PLURALS_TS_FILE
+            AND NOT "${source_lang}" IN_LIST QT_I18N_TRANSLATED_LANGUAGES)
             set(arg_PLURALS_TS_FILE
-                "${arg_TS_FILE_DIR}/${arg_TS_FILE_BASE}_${QT_I18N_SOURCE_LANGUAGE}.ts")
+                "${arg_TS_FILE_DIR}/${arg_TS_FILE_BASE}_${source_lang}.ts")
         endif()
     endif()
 
diff --git a/src/linguist/linguist/doc/cmake-macros.qdoc b/src/linguist/linguist/doc/cmake-macros.qdoc
index cef8dde2c..070860fa1 100644
--- a/src/linguist/linguist/doc/cmake-macros.qdoc
+++ b/src/linguist/linguist/doc/cmake-macros.qdoc
@@ -212,17 +212,17 @@ Pass \c{NO_GLOBAL_TARGET} to \c{qt_add_lupdate} to prevent this behavior.
 The name of this target can be overridden by setting the variable
 \c{QT_GLOBAL_LUPDATE_TARGET} before calling \c{qt_add_lupdate}.
 
-//! [ts-native-language]
-\section1 Native Language
+//! [plurals-ts-file]
+\section1 Plural Forms
 
-The native language of a project is the language in which the source code
+\l QT_I18N_SOURCE_LANGUAGE specifies the language in which the source code
 strings are written. For handling plural forms correctly, create an additional
 \c{.ts} file for that language that only contains translatable strings for
 plural forms. See \l{Handle Plural Forms} for details.
 
-With \c PLURALS_TS_FILE you can specify the \c{.ts} file for the native language.
-This file will only contain plural forms.
-//! [ts-native-language]
+With \c PLURALS_TS_FILE you can specify the \c{.ts} file for the source
+language. This file will only contain plural forms.
+//! [plurals-ts-file]
 
 \section1 Deprecated Command Signature
 
@@ -361,6 +361,7 @@ qt_add_translations([target]
                     [TS_FILE_DIR directory]
                     [TS_FILES file1.ts [file2.ts ...]]
                     [PLURALS_TS_FILE file.ts]
+                    [NO_GENERATE_PLURALS_TS_FILE]
                     [RESOURCE_PREFIX prefix]
                     [OUTPUT_TARGETS variable-name]
                     [QM_FILES_OUTPUT_VARIABLE variable-name]
@@ -431,10 +432,41 @@ argument.
 By default, the \c{.ts} file names are constructed from \c{PROJECT_NAME}. You
 can specify a different base name with the \c{TS_FILE_BASE} argument.
 
-\include cmake-macros.qdoc ts-native-language
+\include cmake-macros.qdoc plurals-ts-file
 
-If \l{QT_I18N_SOURCE_LANGUAGE} is set then the path to the native \c{.ts} file
-will also be automatically determined.
+A plurals-only \c{.ts} is automatically generated unless the option \c
+NO_GENERATE_PLURALS_TS_FILE is specified.
+
+For example,
+\badcode
+project(myapp)
+qt_standard_project_setup(
+    I18N_SOURCE_LANGUAGE en         # optional - this is the default
+    I18N_TRANSLATED_LANGUAGES de
+)
+qt_add_executable(myapp ...)
+...
+qt_add_translations(myapp)
+\endcode
+creates the full translation file \c{myapp_de.ts} and the plurals-only file
+\c{myapp_en.ts}.
+
+If you need a full translation of the source language, add it to
+\l{QT_I18N_TRANSLATED_LANGUAGES}
+
+For example,
+\badcode
+project(myapp)
+qt_standard_project_setup(I18N_TRANSLATED_LANGUAGES en de)
+qt_add_executable(myapp ...)
+...
+qt_add_translations(myapp)
+\endcode
+creates the full translation files
+\list
+\li \c{myapp_en.ts}
+\li \c{myapp_de.ts}
+\endlist
 
 \section1 Options
 
diff --git a/tests/auto/cmake/linguist/test_i18n_auto_ts_file_names/CMakeLists.txt b/tests/auto/cmake/linguist/test_i18n_auto_ts_file_names/CMakeLists.txt
index 08507388f..04e84edd4 100644
--- a/tests/auto/cmake/linguist/test_i18n_auto_ts_file_names/CMakeLists.txt
+++ b/tests/auto/cmake/linguist/test_i18n_auto_ts_file_names/CMakeLists.txt
@@ -21,6 +21,7 @@ foreach(f IN LISTS old_ts_files)
 endforeach()
 
 set(expected_files "")
+set(unexpected_files "")
 
 # Check defaults for the deferred call.
 my_add_library(lib1 STATIC lib.cpp)
@@ -84,12 +85,27 @@ qt_add_translations(TARGETS lib8)
 list(APPEND expected_files
     "${CMAKE_CURRENT_SOURCE_DIR}/test_i18n_auto_ts_file_names_nl.ts")
 
+# Check whether we can turn off the generation of the plurals-only file.
+my_add_library(lib10 STATIC lib.cpp)
+set(QT_I18N_TRANSLATED_LANGUAGES cy)
+set(QT_I18N_SOURCE_LANGUAGE an)
+qt_add_translations(TARGETS lib10 NO_GENERATE_PLURALS_TS_FILE)
+list(APPEND expected_files
+    "${CMAKE_CURRENT_SOURCE_DIR}/test_i18n_auto_ts_file_names_cy.ts")
+list(APPEND unexpected_files
+    "${CMAKE_CURRENT_SOURCE_DIR}/test_i18n_auto_ts_file_names_an.ts")
+
 function(check_ts_file_paths)
     foreach(filepath IN LISTS expected_files)
         if(NOT EXISTS "${filepath}")
             message(FATAL_ERROR "Expected file '${filepath}' does not exist.")
         endif()
     endforeach()
+    foreach(filepath IN LISTS unexpected_files)
+        if(EXISTS "${filepath}")
+            message(FATAL_ERROR "File '${filepath}' unexpectedly exists.")
+        endif()
+    endforeach()
 endfunction()
 
 if(CMAKE_VERSION VERSION_LESS "3.19")