Allow loading of empty translation files

Do not return false for loading an empty .qm file - that is, a valid
file without any translations. We're already shipping empty .qm
files for English translations of Qt since a while, mainly as a
stop for the QTranslator::load(const QLocale &, ...) logic.

Note that QCoreApplication::installTranslator() will still return
false for an empty translation file - which is ok, because it
arguably does not make much sense to install it.

[ChangeLog][QtCore][QTranslator] It is now possible to load qm files
without any translations. This is particularly useful for the
language the untranslated strings are written in; logic to
load translations can now handle the source language like all
other languages.

Task-number: QTBUG-31031
Change-Id: Ibcb84aa755538cb2fa21b14f8635295a58440bbb
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>

7 files changed, 46 insertions, 30 deletions

diff --git a/src/corelib/kernel/qtranslator.cpp b/src/corelib/kernel/qtranslator.cpp
index 23985eb2e9..744bbfbff5 100644
--- a/src/corelib/kernel/qtranslator.cpp
+++ b/src/corelib/kernel/qtranslator.cpp
@@ -533,7 +533,7 @@ bool QTranslatorPrivate::do_load(const QString &realname, const QString &directo
         // memory, so no need to use QFile to copy it again.
         Q_ASSERT(!d->resource);
         d->resource = new QResource(realname);
-        if (resource->isValid() && !resource->isCompressed() && resource->size() > MagicLength
+        if (resource->isValid() && !resource->isCompressed() && resource->size() >= MagicLength
                 && !memcmp(resource->data(), magic, MagicLength)) {
             d->unmapLength = resource->size();
             d->unmapPointer = reinterpret_cast<char *>(const_cast<uchar *>(resource->data()));
@@ -553,7 +553,7 @@ bool QTranslatorPrivate::do_load(const QString &realname, const QString &directo
             return false;
 
         qint64 fileSize = file.size();
-        if (fileSize <= MagicLength || quint32(-1) <= fileSize)
+        if (fileSize < MagicLength || quint32(-1) <= fileSize)
             return false;
 
         {
@@ -858,8 +858,6 @@ bool QTranslatorPrivate::do_load(const uchar *data, int len, const QString &dire
         data += blockLen;
     }
 
-    if (dependencies.isEmpty() && (!offsetArray || !messageArray))
-        ok = false;
     if (ok && !isValidNumerusRules(numerusRulesArray, numerusRulesLength))
         ok = false;
     if (ok) {
@@ -1138,8 +1136,8 @@ QString QTranslator::translate(const char *context, const char *sourceText, cons
 bool QTranslator::isEmpty() const
 {
     Q_D(const QTranslator);
-    return !d->unmapPointer && !d->unmapLength && !d->messageArray &&
-           !d->offsetArray && !d->contextArray && d->subTranslators.isEmpty();
+    return !d->messageArray && !d->offsetArray && !d->contextArray
+            && d->subTranslators.isEmpty();
 }
 
 QT_END_NAMESPACE
diff --git a/tests/auto/corelib/kernel/qtranslator/android_testdata.qrc b/tests/auto/corelib/kernel/qtranslator/android_testdata.qrc
index b33995ef21..39b85db664 100644
--- a/tests/auto/corelib/kernel/qtranslator/android_testdata.qrc
+++ b/tests/auto/corelib/kernel/qtranslator/android_testdata.qrc
@@ -1,6 +1,7 @@
 <RCC>
     <qresource prefix="/android_testdata">
         <file>hellotr_la.qm</file>
+        <file>hellotr_empty.qm</file>
         <file>msgfmt_from_po.qm</file>
         <file>dependencies_la.qm</file>
     </qresource>
diff --git a/tests/auto/corelib/kernel/qtranslator/hellotr_empty.qm b/tests/auto/corelib/kernel/qtranslator/hellotr_empty.qm
new file mode 100644
index 0000000000..be651eede2
--- /dev/null
+++ b/tests/auto/corelib/kernel/qtranslator/hellotr_empty.qm
@@ -0,0 +1 @@
+<¸dÊÍ!¿`¡½Ý
\ No newline at end of file
diff --git a/tests/auto/corelib/kernel/qtranslator/hellotr_empty.ts b/tests/auto/corelib/kernel/qtranslator/hellotr_empty.ts
new file mode 100644
index 0000000000..85e0d3992b
--- /dev/null
+++ b/tests/auto/corelib/kernel/qtranslator/hellotr_empty.ts
@@ -0,0 +1,3 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!DOCTYPE TS>
+<TS version="2.1"/>
diff --git a/tests/auto/corelib/kernel/qtranslator/qtranslator.pro b/tests/auto/corelib/kernel/qtranslator/qtranslator.pro
index d8924c2d5f..a985f35a14 100644
--- a/tests/auto/corelib/kernel/qtranslator/qtranslator.pro
+++ b/tests/auto/corelib/kernel/qtranslator/qtranslator.pro
@@ -5,5 +5,5 @@ SOURCES = tst_qtranslator.cpp
 RESOURCES += qtranslator.qrc
 
 android:!android-embedded: RESOURCES += android_testdata.qrc
-else: TESTDATA += dependencies_la.qm hellotr_la.qm msgfmt_from_po.qm
+else: TESTDATA += dependencies_la.qm hellotr_empty.qm hellotr_la.qm msgfmt_from_po.qm
 
diff --git a/tests/auto/corelib/kernel/qtranslator/qtranslator.qrc b/tests/auto/corelib/kernel/qtranslator/qtranslator.qrc
index 333dcfaa21..cb82c6cc95 100644
--- a/tests/auto/corelib/kernel/qtranslator/qtranslator.qrc
+++ b/tests/auto/corelib/kernel/qtranslator/qtranslator.qrc
@@ -1,5 +1,6 @@
 <RCC>
     <qresource prefix="/tst_qtranslator">
         <file>hellotr_la.qm</file>
+        <file>hellotr_empty.qm</file>
     </qresource>
 </RCC>
diff --git a/tests/auto/corelib/kernel/qtranslator/tst_qtranslator.cpp b/tests/auto/corelib/kernel/qtranslator/tst_qtranslator.cpp
index 451f96339e..40a29c723c 100644
--- a/tests/auto/corelib/kernel/qtranslator/tst_qtranslator.cpp
+++ b/tests/auto/corelib/kernel/qtranslator/tst_qtranslator.cpp
@@ -41,13 +41,12 @@ protected:
 private slots:
     void initTestCase();
 
+    void load_data();
     void load();
-    void load2();
     void threadLoad();
     void testLanguageChange();
     void plural();
     void translate_qm_file_generated_with_msgfmt();
-    void loadFromResource();
     void loadDirectory();
     void dependencies();
     void translationInThreadWhileInstallingTranslator();
@@ -106,24 +105,45 @@ bool tst_QTranslator::eventFilter(QObject *, QEvent *event)
     return false;
 }
 
-void tst_QTranslator::load()
+void tst_QTranslator::load_data()
 {
+    QTest::addColumn<QString>("filepath");
+    QTest::addColumn<bool>("isEmpty");
+    QTest::addColumn<QString>("translation");
 
-    QTranslator tor( 0 );
-    tor.load("hellotr_la");
-    QVERIFY(!tor.isEmpty());
-    QCOMPARE(tor.translate("QPushButton", "Hello world!"), QLatin1String("Hallo Welt!"));
+    QTest::newRow("hellotr_la") << "hellotr_la.qm" << false << "Hallo Welt!";
+    QTest::newRow("hellotr_empty") << "hellotr_empty.qm" << true << "";
 }
 
-void tst_QTranslator::load2()
+void tst_QTranslator::load()
 {
-    QTranslator tor( 0 );
-    QFile file("hellotr_la.qm");
-    file.open(QFile::ReadOnly);
-    QByteArray data = file.readAll();
-    tor.load((const uchar *)data.constData(), data.length());
-    QVERIFY(!tor.isEmpty());
-    QCOMPARE(tor.translate("QPushButton", "Hello world!"), QLatin1String("Hallo Welt!"));
+    QFETCH(QString, filepath);
+    QFETCH(bool, isEmpty);
+    QFETCH(QString, translation);
+
+    {
+        QTranslator tor;
+        QVERIFY(tor.load(QFileInfo(filepath).baseName()));
+        QCOMPARE(tor.isEmpty(), isEmpty);
+        QCOMPARE(tor.translate("QPushButton", "Hello world!"), translation);
+    }
+
+    {
+        QFile file(filepath);
+        file.open(QFile::ReadOnly);
+        QByteArray data = file.readAll();
+        QTranslator tor;
+        QVERIFY(tor.load((const uchar *)data.constData(), data.length()));
+        QCOMPARE(tor.isEmpty(), isEmpty);
+        QCOMPARE(tor.translate("QPushButton", "Hello world!"), translation);
+    }
+
+    {
+        QTranslator tor;
+        QVERIFY(tor.load(QString(":/tst_qtranslator/%1").arg(filepath)));
+        QCOMPARE(tor.isEmpty(), isEmpty);
+        QCOMPARE(tor.translate("QPushButton", "Hello world!"), translation);
+    }
 }
 
 class TranslatorThread : public QThread
@@ -240,14 +260,6 @@ void tst_QTranslator::translate_qm_file_generated_with_msgfmt()
     qApp->removeTranslator(&translator);
 }
 
-void tst_QTranslator::loadFromResource()
-{
-    QTranslator tor;
-    tor.load(":/tst_qtranslator/hellotr_la.qm");
-    QVERIFY(!tor.isEmpty());
-    QCOMPARE(tor.translate("QPushButton", "Hello world!"), QLatin1String("Hallo Welt!"));
-}
-
 void tst_QTranslator::loadDirectory()
 {
     QString current_base = QDir::current().dirName();