A while back I dabbled with Fossil SCM. I liked parts of it but ended up returning to git. During that experiment,
I created a fair bit of content in Fossil and wanted to get it out. I assumed this would be easy because I’d
used the Fossil export command previously to create a git-fast-import-compatible text file with all of the
repo contents. This time, however, I was met with this error upon import:
fast-import error: fatal: mark :685 not declared
Disappointing. But the fast-import format is plain text so I decided to take a look at a bazillion lines in Vim. Even without any knowledge of the format, it was easy to grok what was going on. A key concept was that “marks” were being defined and referred to later. But mark :685 was being referenced before it was ever created, which is presumably a bug in Fossil.
I just moved the whole mark :685 section to the top of the file, reran git-fast-import, and everything worked!