Unify alias and default command parsing

[gtsiam]

I'm trying to pull config parsing out of the cli. But to do that, we need to untangle config parsing and argument parsing. This is part of that.

As a bonus, you can now specify single-comamnd aliases as a string.

Checklist

If applicable:

• I have updated CHANGELOG.md
• I have updated the documentation (README.md, docs/, demos/)
• I have updated the config schema (cli/src/config-schema.json)
• I have added tests to cover my changes

[gtsiam]

Also, do we really want to forbid the user from aliasing built-in commands?

[bnjmnt4n]

I'm trying to pull config parsing out of the cli. But to do that, we need to untangle config parsing and argument parsing. This is part of that.

Any reason for this?

As a bonus, you can now specify aliases some of the simpler aliases/default commands as a space-delimited string.

This wouldn't correctly handle cases where one of the arguments is a quoted string with whitespace within, would it? I'm not sure if there's a good enough justification for this then.

[gtsiam]

Any reason for this?

#3034 Comes to mind. But my understanding is that we want to make using the jj-lib actually reasonably doable anyway. Currently, if you look at run_internal, you'll see that it's a mess of parsing the command line arguments, then the config then args again then re-parsing with a slightly different config etc, etc.

This wouldn't correctly handle cases where one of the arguments is a quoted string with whitespace within, would it? I'm not sure if there's a good enough justification for this then.

Not it wouldn't, and intentionally so. I don't want to implement a shell here. This is just a convenience thing that I've found myself personally wanting. If you want argument parsing, there's always the full array syntax. The alternative would be to treat single strings as single arguments, but that would go counter to what I would expect. (Also, see what git does).

That said, we could forbid quotes (", ' and `) to prevent this particular footgun. In fact I'm gonna do that right now.

[yuja]

cc @matts1 as he was working on #3673

[gtsiam]

I'll remove whitespace splitting and restore the old behaviour for now

[gtsiam]

Ok, this is just the refactor now. I tried to do too much in one pr I think.

Only real change now should be that you can specify single-command (no argument) aliases with a string. This is already possible for default-command, but now it is also possible in aliases.

[martinvonz]

cli: simplify argument expansion code

Could you add some more detail? This patch adds 39 lines of code, so it's not an obvious simplification. It would be good to know why you're doing it (if it's not only to make the code simpler). Since it's a non-trivial patch, it's also good to explain how you're refactoring the code so the readers don't have to spend so much time to try to figure out what's going on.