Compare directories (on diff. drives) by content

[georgeb]

Syncdir would still treat pseudo-unique files as unique and synchronize this old way.

Almost - yet not quite. "SyncDirs" would first move all the pseudo-unique files (identified as duplicates) into those newly introduced sub-categories "Locally unique" on both sides (possibly colored in light-blue/light-green) and making them separately selectable by split top-level-selection-buttons (then resulting in a total number of 6 instead of 4 as of now). All 6 groups could then be synchronized (after proper file-selection) - individually or all together - in conventional manner.

If the duplicates are in different locations (has been moved or copied) how would their locations be displayed in syncdir extension to make it clear?

In exactly the same manner as they are displayed now - each file beneath its parent-directory-header (left/right). The only - yet significant - difference then being that all the duplicates among the (pseudo)-unique columns/categories would now be represented in a different font-color indicating that they DO HAVE binary duplicates someplace else.

What should be displayed and how, to make it visually as easy as possible for inspecting resp. deciding what to do with content-duplicates? Their filename, path, position in the tree, date, attributes?

All that would be needed for e.g. individual, visual inspection is the well-proven mode of display-structure that "SyncDirs" currently already offers by default. BUT THE DIFFERENT COLOR-REPRESENTATION WOULD NOW DRAW THE USER'S ATTENTION TO THE FACT THAT HE NOW HAS TO DEAL WITH A DUPLICATE and thereby inform him that this very file possibly needs individual attention and decision-making. Whereas in the current state of operation the user would be left in the dark about that fact and thus would (wrongly) assume that this is just another TRULY UNIQUE file.

You could create a graphical representation of your proposal, maybe it would be clearer than 1000 words. If we could see the final look, then we could look for answers on how to functionally achieve it.

I am no graphics-expert - so that would be hard for me to achieve. Just think of an ordinary "SyncDirs"-standard-screen with 2 new, additional font-colors to represent only the duplicates for the left and right side (possiby light-blue and light-green) and a total of then 6 (instead of now 4) top-level-selection-buttons enabling separate selection of each of the then 6 sub-categories being:
1. (Truly) Unique left
2. (Files with) Duplicates left
3. Identical
4. Different
5. (Files with) Duplicates right
6. (Truly) Unique right

That's about all needed to describe (and imagine) the look of the enhanced tool. Plus an identical "SyncDirs"-standard-screen-pop-up-window offering to display ONLY ONE SINGLE GROUP of binary duplicate-files, perhaps offering to cycle through all the other groups of binary-duplicates via the cursor-keys. That would be all.