QMimeDatabase: fix regression in alias resolving

The refactoring to support multiple providers broke alias resolving
(e.g. "text/directory" would be an invalid mimetype, instead of being
resolved to "text/vcard"). The unittest didn't catch it because most of
it was running with a single mime directory (and therefore a single provider,
in the new model). Fixed by re-running a number of test methods once we
have a second mime directory.

Change-Id: Ib5da89ba79c11ed41813b2aff4bc71c30afcde7d
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/mimetypes/qmimeprovider.cpp

@@ -401,7 +401,7 @@ QString QMimeBinaryProvider::resolveAlias(const QString &name)
             return QLatin1String(mimeType);
         }
     }
-    return name;
+    return QString();
 }
 
 void QMimeBinaryProvider::addAliases(const QString &name, QStringList &result)
@@ -729,7 +729,7 @@ void QMimeXMLProvider::addAliases(const QString &name, QStringList &result)
 
 QString QMimeXMLProvider::resolveAlias(const QString &name)
 {
-    return m_aliases.value(name, name);
+    return m_aliases.value(name);
 }
 
 void QMimeXMLProvider::addAlias(const QString &alias, const QString &name)

tests/auto/corelib/mimetypes/qmimedatabase/tst_qmimedatabase.cpp

@@ -1045,6 +1045,31 @@ void tst_QMimeDatabase::installNewLocalMimeType()
     QCOMPARE(db.mimeTypeForFile(qmlTestFile).name(),
              QString::fromLatin1("text/x-qml"));
 
+    // Now that we have two directories with mime definitions, check that everything still works
+    inheritance();
+    if (QTest::currentTestFailed())
+        return;
+
+    aliases();
+    if (QTest::currentTestFailed())
+        return;
+
+    icons();
+    if (QTest::currentTestFailed())
+        return;
+
+    comment();
+    if (QTest::currentTestFailed())
+        return;
+
+    mimeTypeForFileWithContent();
+    if (QTest::currentTestFailed())
+        return;
+
+    mimeTypeForName();
+    if (QTest::currentTestFailed())
+        return;
+
     // Now test removing local mimetypes
     for (int i = 1 ; i <= 3 ; ++i)
         QFile::remove(destDir + QStringLiteral("invalid-magic%1.xml").arg(i));