Implement loading justfile from stdin

[drzymalanet]

I think it would be nice to have the possibility to pipe justfiles into just, like so:

cat input.txt | just --dump --justfile - > output.txt

It would work by detecting a special symbol "-" as the -f / --justfile argument.

Benefits:

• Some code editors like helix require this in order to make auto formatting to work,
• Many command line tools work like this and it seems it will not hurt to have,

The plan:

1. Move Search{} functionality into Source{}
2. Implement Source::from_stdin()
3. Add "-" detection to the argument parser.

Here is the first of the commits, more commits will be added while work progresses.

[casey]

This seems reasonable, but this PR looks a bit too complicated and I think some of the changes are unnecessary.

I would create two new SearchConfig variants, WithStdin, and WithStdinAndWorkingDirectory, and handle those two cases separately in Search::find.

[drzymalanet]

@casey I have added the variants, now we need to change Search.justfile type because it is a PathBuf which does not fit to the stdin stream. It seems to me that changing it to an Rc<dyn std::io::Read> or a custom JustfileSource would be some options. What do you think?

[casey]

There are two options I can think of:

1. Add an additional field to Search, which is a string containing the loaded source
2. Make Search::justfile an enum, like JustfileSource

I would try out 1 first and see how it looks and see if it causes any problems, or requires a big refactor.

[drzymalanet]

Sorry for closing and reopening. It was by mistake.

@casey Please have a look at the new commit. I have added a JustfileKind enum to the Search struct. It does not feel right, but I have no idea how to make it better without a bigger refactor. Let me know what you think.

[casey]

This looks like a good approach to me!