Here is a personal list of bugs and feature requests for the Unison file synchronizer. These issues refer to the text-based user interface (which is the one I use). At the time of this writing (18 August 2015) the latest Unison version is 2.48.3.
To my knowledge, Unison is the most standard and straightforward file synchronizer for Linux. Many people say they now use 'git' or some other revision control software for situations where they would have used "Unison" in the past, but I still find Unison to be preferable for many tasks. In many cases, such as sharing configuration files between systems, I am not interested in storing an annotated revision history of changes I make. Using revision control to deal with conflicts in my own files seems cumbersome. A file synchronizer like Unison solves the problem with less hassle.
While reacquainting myself with Unison recently, I made a list of problems that I ran into. It would be great if someone has time to fix them!
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For certain command-line options, such as 'backup' or 'merge', running unison on two single-file roots triggers an exception failure in 'path.ml'. Reported here in 2009: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=517240 and here in 2015: http://lists.seas.upenn.edu/pipermail/unison-hackers/2015-July/001849.html
According to my testing, this seems to affect Unison versions all the way from 2001! However, the bug could also have been caused by more recent changes in the O'Caml string library, we're not sure.
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The help text for 'g' (currently: "proceed immediately to propagating changes") should make it clear that this will propagate all future recommended changes, rather than just the ones that the user has already approved. The first few years I used Unison, I thought that 'g' meant "I've approved changes to a number of paths already, now I want to save my place by propagating just the changes I entered, skipping the rest of the paths". Instead it seems to mean "I want to propagate the changes I approved, as well as approving and propagating all the changes that Unison is about to recommend to me" - in other words "switch to batch mode now" - which seems less useful. Because the user doesn't control the order in which conflicts are presented, I don't see the value of being able to switch from interactive to batch mode mid-sync.
This is a UI bug, but it could result in data loss in certain situations by triggering unintended "batch" syncs which propagate changes in the wrong direction. It potentially affects not only beginning users, but also experienced users who have read the entire documentation, since it's not documented.
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Related to the above, there should be an option to "skip" all remaining paths, for users who are satisfied with the changes they've authorized so far and want save their work by propagating these changes before continuing. Perhaps this should be what 'g' actually does.
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There should be an option (or default) to ask for confirmation when the user presses 'q' for 'quit', especially if changes have been authorized. Sometimes I accidentally press 'q' and lose some work, which is annoying. For instance, the results of 'diff' are usually displayed to me in a pager, but sometimes there is no pager (e.g. if I run unison with sudo). If I press 'q' out of habit to exit a non-existent pager, it instead exits Unison. If I press 'q' twice by accident, it exits Unison.
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The help list starts out with three "ignore permanently" commands, which I think makes it easy to miss the fact that there is an option to essentially "ignore the path temporarily" down at the bottom ("skip"). I would move the 'skip' option nearer to this group, perhaps before it, in the Commands: help list, and perhaps rename to 'skip this path' for consistency with other command descriptions.
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Typing 'p' for 'previous' doesn't work after 'I' for 'ignore permanently'.
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The 'root alias' option would be more useful if I didn't have to specify every possible "root" under a given directory or host. For instance, if I'm aliasing //hostB// to //hostA//, I think that should by default map //hostA/root1/ to //hostB/root1/ as well, since the prefix matches. In the current version of Unison I need a separate 'rootalias' option for subdirectories. This could be annoying if, for example, I have several roots on a host and I want to change the hostname.
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In diff output, it would be nice to be able to provide more informative file names. Instead of this:
--- /home/frederik/.Xdefaults.unison.diff- 2015-07-30 17:17:20.353393267 -0700 +++ /home/frederik/.Xdefaults 2015-07-30 17:17:12.363370611 -0700we could be looking at
--- //host1//home/frederik/.Xdefaults 2015-07-30 17:17:20.353393267 -0700 +++ //host2//home/frederik/.Xdefaults 2015-07-30 17:17:12.363370611 -0700The GNU diff lets us specify these header path strings with the "--label=" option. To allow us to make use of this feature, Unison would need to give us the pretty path names in variables (e.g. HOSTPATH1 and HOSTPATH2) for substitution in the 'diff =' configuration option.
Also see: https://wiki.archlinux.org/index.php/Unison#More_helpful_diff_output This is a suggestion for making Unison's 'diff' output more readable, which could be mentioned in the manual or turned into a default.
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When a new file has been created in one root, 'd' for 'diff' should display the contents of the file (e.g. by diffing against /dev/null).
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It's strange that "ignore = " allows pattern matching, but "path = " does not. What if I want to use Unison to merge every dot file in my home directory? The inability to use patterns to define groups of files makes it difficult. I guess this is a very basic design decision which would be difficult to change, but I noticed it has been brought up before on the mailing list. As far as I can tell from the documentation, 'ignorenot' does not serve as a workaround.
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If I accidentally put a pattern instead of a literal path into a "path = " specification, the GUI gives me an error ("Filesystem watcher error"), but the text-based interface doesn't even give a warning. A warning would be nice.
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When I first start Unison, I see hostnames written above two columns. The columns may contain text like "changed" or "new file". However, if I press 'd', or '?', or 'l', or if I simply go through a lot of paths, I lose the host names header, and then I get '>' and '<' confused. It would be convenient if various commands which produce lots of output would finish by printing the column headers again as a reminder.
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I tried to use 'merge = ' to specify a merge command which runs in the terminal, but this didn't work. Instead I had to make the command open an xterm with my merge program running inside it. It would be nice for Unison to give the 'merge' command access to the terminal. This would provide a simpler interface, and make debugging the merge command easier. Of course, GUI users would have to provide a different merge command.