CMake: Fix deferred qt_add_translations calls...

...if find_package(Qt6Core) is missing at the project directory level.

Consider a project with a subdir. In the subdir, we have
    find_package(Qt6 COMPONENTS Widgets LinguistTools ...)
    ...
    qt_add_translations(mytarget TS_FILES mytarget_de.ts ...)
such that the actual qt_add_translations call is deferred.

In the top-level CMakeLists.txt we have no find_package call for Qt6.

Then the deferred call will fail, because we defer to the project root,
and there we're missing variables that have been pulled in by the
find_package(Qt6 ...) call in the subdir.

Fix this by adding a find_package(Qt6 ...) call when we're deferring
qt_add_translations. The find_package call will do (almost) nothing if
the packages have already been loaded.

Pick-to: 6.7 6.8
Fixes: QTBUG-126167
Change-Id: I2083ebecfd64e67649906526d2f99bb202b03cb8
Reviewed-by: Alexandru Croitor <[email protected]>

Author: jobor

src/linguist/Qt6LinguistToolsMacros.cmake

@@ -648,6 +648,14 @@ function(qt6_add_translations)
                 endif()
             endforeach()
 
+            # The project-level CMakeLists.txt might miss a call to find_package(Qt6 COMPONENTS Core
+            # LinguistTools). Then, subsequent function calls like qt_add_resources will fail. To
+            # remedy this, pull the packages in.
+            cmake_language(EVAL CODE
+                "cmake_language(DEFER
+                    DIRECTORY \"${PROJECT_SOURCE_DIR}\"
+                    CALL find_package Qt6 COMPONENTS Core LinguistTools)")
+
             # Schedule this command to be called at the end of the project's source dir.
             cmake_language(EVAL CODE
                 "cmake_language(DEFER

tests/auto/cmake/linguist/CMakeLists.txt

@@ -66,5 +66,6 @@ _qt_internal_test_expect_pass(test_i18n_exclusion)
 _qt_internal_test_expect_pass(test_i18n_filter_autogen_files)
 _qt_internal_test_expect_pass(test_i18n_source_language)
 if(NOT CMAKE_CROSSCOMPILING)
+    _qt_internal_test_expect_pass(test_i18n_find_package_in_subdir BINARY app1)
     _qt_internal_test_expect_pass(test_i18n_subdir BINARY app1)
 endif()

tests/auto/cmake/linguist/test_i18n_find_package_in_subdir/CMakeLists.txt

@@ -0,0 +1,7 @@
+# Copyright (C) 2024 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+
+cmake_minimum_required(VERSION 3.16)
+project(test_i18n_subdir)
+set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}")
+add_subdirectory(subdir)

tests/auto/cmake/linguist/test_i18n_find_package_in_subdir/subdir/CMakeLists.txt

@@ -0,0 +1,10 @@
+# Copyright (C) 2024 The Qt Company Ltd.
+# SPDX-License-Identifier: BSD-3-Clause
+find_package(Qt6 COMPONENTS Gui LinguistTools)
+qt_add_executable(app1
+    main.cpp)
+target_link_libraries(app1 PRIVATE Qt::Gui)
+qt_add_translations(app1
+    TS_FILES app1_de.ts
+    NO_GENERATE_PLURALS_TS_FILE
+)

tests/auto/cmake/linguist/test_i18n_find_package_in_subdir/subdir/app1_de.ts

@@ -0,0 +1,12 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!DOCTYPE TS>
+<TS version="2.1" language="de_DE">
+<context>
+    <name>main</name>
+    <message>
+        <location filename="main.cpp" line="17"/>
+        <source>Hello from main!</source>
+        <translation>Hallo aus der Hauptfunktion!</translation>
+    </message>
+</context>
+</TS>

tests/auto/cmake/linguist/test_i18n_find_package_in_subdir/subdir/main.cpp

@@ -0,0 +1,32 @@
+// Copyright (C) 2024 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only
+
+#include <QtCore/QCoreApplication>
+#include <QtCore/QTranslator>
+
+#include <iostream>
+
+int main(int argc, char *argv[])
+{
+    QCoreApplication app(argc, argv);
+
+    const QString qmFile = ":/i18n/app1_de.qm";
+    std::cout << "Loading translation '" << qPrintable(qmFile) << "'..." << std::endl;
+    QTranslator *translator = new QTranslator(&app);
+    if (!translator->load(qmFile)) {
+        std::cerr << "Error: failed to load the translation" << std::endl;
+        return 1;
+    }
+    app.installTranslator(translator);
+
+    std::cout << "Checking translated text..." << std::endl;
+    const QString translated = QCoreApplication::translate("main", "Hello from main!");
+    if (!translated.startsWith("Hallo aus")) {
+        std::cerr << "Error: translation doesn't seem to work. "
+                  << "The translated text is '" << qPrintable(translated) << "'" << std::endl;
+        return 2;
+    }
+
+    std::cout << "All good." << std::endl;
+    return 0;
+}