QMimeDatabase: handle buggy type definitions with circular inheritance

This fixes an infinite loop reported by a user who had both the
definition of text/javascript from shared-mime-info 2.3 and the
definition of text/javascript from shared-mime-info 2.4 installed at the
same time. In 2.3, text/javascript is a subtype of
application/ecmascript, but in 2.4 application/ecmascript is a subtype
of text/javascript. Having both at the same time resulted in circular
inheritance.

https://gitlab.freedesktop.org/xdg/shared-mime-info/-/merge_requests/258#note_2167707

[ChangeLog][QtCore][QMimeDatabase] Added code to detect and break
circular inheritance loops in the MIME data, which were causing infinite
loops

Pick-to: 6.6 6.5
Change-Id: Ic207b1593a49c7bb88e4fd810d8f88aa630087ce
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: David Faure <david.faure@kdab.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/tests/auto/corelib/mimetypes/qmimedatabase/tst_qmimedatabase.cpp b/tests/auto/corelib/mimetypes/qmimedatabase/tst_qmimedatabase.cpp
index 9bc3037c99..d7db4bb9bf 100644
--- a/tests/auto/corelib/mimetypes/qmimedatabase/tst_qmimedatabase.cpp
+++ b/tests/auto/corelib/mimetypes/qmimedatabase/tst_qmimedatabase.cpp
@@ -48,6 +48,7 @@ static const std::array additionalLocalMimeFiles = {
     "invalid-magic2.xml",
     "invalid-magic3.xml",
     "magic-and-hierarchy.xml",
+    "circular-inheritance.xml",
     "webm-glob-deleteall.xml",
 };
 
@@ -388,6 +389,13 @@ void tst_QMimeDatabase::inheritance()
     const QMimeType mswordTemplate = db.mimeTypeForName(QString::fromLatin1("application/msword-template"));
     QVERIFY(mswordTemplate.isValid());
     QVERIFY(mswordTemplate.inherits(QLatin1String("application/msword")));
+
+    // Check that buggy type definitions that have circular inheritance don't cause an infinite
+    // loop, especially when resolving a conflict between the file's name and its contents
+    const QMimeType ecmascript = db.mimeTypeForName(QString::fromLatin1("application/ecmascript"));
+    QVERIFY(ecmascript.allAncestors().contains("text/plain"));
+    const QMimeType javascript = db.mimeTypeForFileNameAndData("xml.js", "<?xml?>");
+    QVERIFY(javascript.inherits(QString::fromLatin1("text/javascript")));
 }
 
 void tst_QMimeDatabase::aliases()