QMimeDatabase: Fix MIME detection issues with magics in MIME hierarchies

Assume two MIME types A and B are registered, both with the same glob
pattern, A being parent of B, A with some magic rule, and B with another
magic rule. Given a file that matches the glob pattern and the magic rule
of A, the resulting MIME type depended on the order of registration of A
and B, because it would just check if some glob matching MIME type was
also a subclass of the magic matching MIME type.

The patch prefers the the MIME type that matches by magic if that
matches by glob pattern as well (i.e. A in our example).

The "recommended checking order" of the spec does handle that case.

Task-number: QTBUG-44846
Change-Id: I2af43f6199faf9a42cd9c35d3a045441afbd6217
Reviewed-by: Eike Ziller <eike.ziller@qt.io>
Reviewed-by: David Faure <david.faure@kdab.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/src/corelib/mimetypes/qmimedatabase.cpp b/src/corelib/mimetypes/qmimedatabase.cpp
index 68e3c8f10d..a58698af53 100644
--- a/src/corelib/mimetypes/qmimedatabase.cpp
+++ b/src/corelib/mimetypes/qmimedatabase.cpp
@@ -382,9 +382,12 @@ QMimeType QMimeDatabasePrivate::mimeTypeForFileNameAndData(const QString &fileNa
 
         // Disambiguate conflicting extensions (if magic matching found something)
         if (candidateByData.isValid() && magicAccuracy > 0) {
-            // "for glob_match in glob_matches:"
-            // "if glob_match is subclass or equal to sniffed_type, use glob_match"
             const QString sniffedMime = candidateByData.name();
+            // If the sniffedMime matches a glob match, use it
+            if (candidatesByName.m_matchingMimeTypes.contains(sniffedMime)) {
+                *accuracyPtr = 100;
+                return candidateByData;
+            }
             for (const QString &m : qAsConst(candidatesByName.m_matchingMimeTypes)) {
                 if (inherits(m, sniffedMime)) {
                     // We have magic + pattern pointing to this, so it's a pretty good match