Invalid argument (please report a bug): String.blit / Bytes.blit_string

[dpkonofa]

I have thoroughly read the Reporting Bugs and Feature Requests wiki page.

Meta

Bug reports must be about a minimized configuration, as described in the wiki page.

People filing bug reports will be expected to follow up and perhaps
test proposed fixes.

Environment

• Unison version - 2.53.7
• OS, version and CPU - macOS Tahoe 26.1
• ocaml version - No idea.
• TUI or GUI - GUI
• local, ssh, socket, or ? local - Drive to Drive sync
• use of fsmonitor? - No

Reproduction Recipe

Open Unison and open the profile that previously worked. Now get:

Fatal Error
Invalid argument (please report a bug): String.blit / Bytes.blit_string
(Exit)

Expected behavior vs actual behavior

Expected behavior is for it to open the project, scan for changes, and prompt to sync. Instead, the dialog prompts me to report a bug.

[dpkonofa]

For reference, I did briefly try to troubleshoot this and thought it might be related to this issue (#331) but, even after renaming the files, there doesn't seem to be a way for me to open this profile or start Unison.

[gdt]

ocaml version is likely not relevant, but please explain where your unison binary came from and how it was compiled.

"drive to drive sync" is unclear. Please explain if you mean both roots are local, and the filesystem type.

Can you reproduce with the TUI?

Can you reproduce with a constructed simple root? You haven't described what is in the roots, and if you synced them before, etc.

[tleedjarv]

When it worked previously, do you know what was the Unison version?

What's interesting is that the error message should include a backtrace but it obviously doesn't. It would really help if you could try the TUI (on the command line, the executable name is unison) with the same profile and report if you see the same error or not.

Another thing that could help with debugging is to try the GTK GUI, but I don't know to get that on the Mac so can't help you there.

[dpkonofa]

please explain where your unison binary came from and how it was compiled.

From here. I just downloaded the released Unison binary for macOS-ARM64 (M4 Max on this machine). I didn't compile anything.

Please explain if you mean both roots are local, and the filesystem type.

Local. I'm syncing 2 external hard drives that have media content on them. I edit and work off of one drive and then have it sync to the other when I'm done as a backup copy that I give to clients. APFS file system on both but there's also an exFAT drive that I tried it with to test and that gave the same error.

Can you reproduce with the TUI?

If TUI means the terminal version of the app then I doubt it. I wouldn't even know what to do to mirror the config I've set up in the UI.

Can you reproduce with a constructed simple root? You haven't described what is in the roots, and if you synced them before, etc.

No sure what this means. The drives just have several folders in them, 1 per client, and inside each folder is a structure for each client based on the project. I did mention in the original post that I have synced them before and have been syncing them successfully for over a year. Today is the first day that anything failed and it won't even let me do anything. As soon as I click to Open the sync I have set up, it fails with that error. I can't edit the Profile or do anything else except Quit or attempt to Open the profile which fails with that pop-up.

[dpkonofa]

When it worked previously, do you know what was the Unison version?

It has worked on every previous Unison version for the last year. I have not attempted to downgrade to an older version yet as the app is what prompted me to submit the bug report.

It would really help if you could try the TUI (on the command line, the executable name is unison) with the same profile and report if you see the same error or not.

Can you give me some further instruction? Where do I find the command line version and what parameters do I need to specify? Up until now, I've only ever used the GUI version of the tool.

Another thing that could help with debugging is to try the GTK GUI, but I don't know to get that on the Mac so can't help you there.

I also do not know anything about the GTK GUI so I also cannot help there.

[dpkonofa]

Some more info. I checked the Unison log in ~/Library/Application Support/ and it shows this message just before these errors:

Unison 2.53.7 (ocaml 4.14.2) finished propagating changes at 11:23:35.55 on 21 Aug 2025, 0.003 s

Warning: the archives are locked.  
If no other instance of unison is running, the locks should be removed.
The file /Users/dpkonofa/Library/Application Support/Unison/lk2e770dc642415ddc80ef3fcbc36c5be6 on host USS-Enterprise-NCC-1701.local should be deleted
Please delete lock files as appropriate and try again.
Warning: the archives are locked.  
If no other instance of unison is running, the locks should be removed.
The file /Users/dpkonofa/Library/Application Support/Unison/lk90639fc94693188846e34d650be03df7 on host USS-Enterprise-NCC-1701.local should be deleted
Please delete lock files as appropriate and try again.
Invalid argument (please report a bug): String.blit / Bytes.blit_string

Invalid argument (please report a bug): String.blit / Bytes.blit_string

Invalid argument (please report a bug): String.blit / Bytes.blit_string

Invalid argument (please report a bug): String.blit / Bytes.blit_string

Invalid argument (please report a bug): String.blit / Bytes.blit_string

Invalid argument (please report a bug): String.blit / Bytes.blit_string

Invalid argument (please report a bug): String.blit / Bytes.blit_string

Unfortunately, neither of those files exist in that folder. I have some other extensionless files in that folder but not the ones mentioned in the error message.

[gdt]

You have a pair of roots that has a problem. You should be able to make a new root and put just one or two things in it and a profile and sync that to a corresponding new root. And then see how that goes. If it works, make it more complicated. If it fails, start over and make it simpler. The point is to find the smallest situation that exhibits the bug, and to be able to turn this into a script that sets up the failing pattern, so others can help debug.

[gdt]

Also I'll note that the CI builds are for CI, and that they install dependencies, and thus likely expect that the same dependencies are on your system. The instructions section for mac is I think marked as needing to be written.

As for TUI there is a manual, and a man page.

[tleedjarv]

Can you give me some further instruction? Where do I find the command line version and what parameters do I need to specify? Up until now, I've only ever used the GUI version of the tool.

Open Terminal or Console (I don't know what it is called in macOS) and then typing unison -ui text -i should work (if you get a "not found" then try /usr/local/bin/unison -ui text -i). That should give you the same list of profiles you see in the GUI.

[tleedjarv]

I checked the Unison log in ~/Library/Application Support/ and it shows this message just before these errors:

I think this message is unrelated.