Fix registration of Windows-specific custom mime types

Data received by Qt from a native clipboard- or drag'n'drop-source is
mapped to a application/x-qt-windows-mime;value=... mime type, where the
"value" corresponds to the native clipboard format name, e.g.
"FileGroupDescriptor". When we register such a mime type in Qt, then we
need to get the same clipboard format number back. I.e. registering
'application/x-qt-windows-mime;value="FileGroupDescriptor"' needs to
produce the same Windows clipboard format identifier as the call to
RegisterClipboardFormat("FileGroupDescriptor").

Otherwise, a mime converter implementation has to operate on different
clipboard format values in the implementations of the different virtual
functions that are operating on FORMATETC data structures.

Task-number: QTBUG-93632
Change-Id: I0b7e3a2fc0e3f72bffc4490fc0ff4b190e0929a3
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

1 files changed, 9 insertions, 3 deletions

diff --git a/src/plugins/platforms/windows/qwindowsmimeregistry.cpp b/src/plugins/platforms/windows/qwindowsmimeregistry.cpp
index b2f9e4289d..55d0266bb2 100644
--- a/src/plugins/platforms/windows/qwindowsmimeregistry.cpp
+++ b/src/plugins/platforms/windows/qwindowsmimeregistry.cpp
@@ -1496,12 +1496,18 @@ void QWindowsMimeRegistry::registerMime(QWindowsMime *mime)
 /*!
     Registers the MIME type \a mime, and returns an ID number
     identifying the format on Windows.
+
+    A mime type \c {application/x-qt-windows-mime;value="WindowsType"} will be
+    registered as the clipboard format for \c WindowsType.
 */
 int QWindowsMimeRegistry::registerMimeType(const QString &mime)
 {
-    const UINT f = RegisterClipboardFormat(reinterpret_cast<const wchar_t *> (mime.utf16()));
-    if (!f)
-        qErrnoWarning("QWindowsApplication::registerMimeType: Failed to register clipboard format");
+    const QString mimeType = isCustomMimeType(mime) ? customMimeType(mime) : mime;
+    const UINT f = RegisterClipboardFormat(reinterpret_cast<const wchar_t *> (mimeType.utf16()));
+    if (!f) {
+        qErrnoWarning("QWindowsMimeRegistry::registerMimeType: Failed to register clipboard format "
+                      "for %s", qPrintable(mime));
+    }
 
     return int(f);
 }