Meld has a --label command line argument that lets you give a label to one of the files that is being compared. This label is shown (instead of the file name) on the meld window title and on the tab handle.

This is particularly useful when meld is called by a source control tool, such as TortoiseHg. For example TortoiseHg will set the label to the revision id of the revisions that are being compared. It does this with comparing single files or when comparing whole revisions, which it does by triggering a directory diff.

The problem is that meld ignores the label command line argument when comparing folders. This makes using meld for comparing whole revisions in TortoiseHg and similar tools very inconvenient.