Oh, heck, I might as well say what it was:
I just typed in
hg revert -r defaultinstead of
hg revert -r default .hgrcMercurial went and scanned my home directory repository, which is rather large, taking 10+ minutes to scan, before it gave me the error message
abort: no files or directories specifiedIt would have been nice if it had reported the error message immediately, instead of scanning the repo.
This isn't just Mercurial specific: other tools have the same problem. Some of them my tools.
It is nice if interactive tools report error messages as soon as possible.
Aspect oriented program might help. Create an aspect for "command line checking", and reorder code that is related to command line checking earlier.
Dataflow analysis might also help. In an ideal world, sans ambiguous points, etc., it would be evident that the error check depended only on the command line, and could be moved up earlier.
This is just part of my not-so-hidden agenda, to apply dataflow everywhere.