cli: diff: add fileset-alias option

[bryceberger]

Following discussion in #4961.

The original problem was wanting to hide paths from the diff view. I failed to read the docs and realize that ~patterns are available, and already solve that.

However, there are a few ergonomic issues with this:

• ~... may be interpreted by the shell, so the excluded paths should be quoted
• Some paths are common to ignore, and annoying to type repeatedly (Cargo.lock, etc)
• Path is even longer if you're not at the root of the repository (~root-file:Cargo.lock)

The template system provides a nice solution for frequently used commands. It would be nice if there was a similar system for filesets.

Example

[fileset-aliases]
no-lock = "~root-glob:*.lock"

jj diff -P no-lock

Open questions:

• Should combining aliases and user-provided paths be allowed?
• Better name / abbreviation? -P was chosen from "P"ath, but I'm not attached to it.

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)

[yuja]

The fileset-aliases idea is to substitute parsed tree of fileset (or path) expression. You can see how this is implemented in cli/src/template_parser.rs and lib/src/revset.rs. (It's a bit odd that alias substitution isn't made in revset_parser.rs, but that's just for a historical reason.) We'll need to write some plumbing code.

[bryceberger]

Ah, so to have something like jj diff no_lock directly use the no_lock alias? In that case, what would happen if the user wants to interact with a file whose name is shadowed by an alias?

[martinvonz]

Ah, so to have something like jj diff no_lock directly use the no_lock alias? In that case, what would happen if the user wants to interact with a file whose name is shadowed by an alias?

Then they would probably have to escape it with e.g. cwd:no_lock

[bryceberger]

Copied implementations from fileset_parser.rs until it worked. The implementation in 6b1e2d3 adds a dsl_util::expand_aliases() step to fileset::parse().

Since this tries to expands all ExpressionKind::Identifier, jj diff <path> no longer always matches <path>, depending on user configuration. Workarounds:

• Quote the path: jj diff '"path"' (double quoted because of shell expansions. This makes an ExpressionKind::String instead of ExpressionKind::Identifier, which is not expanded.)
• Add a file pattern: jj diff file:path

[yuja]

Since this tries to expands all ExpressionKind::Identifier, jj diff <path> no longer always matches <path>, depending on user configuration. Workarounds:

Correct. It's up to user to choose sane alias symbols such as NO_LOCK (assuming file names are usually lower case), no_lock() (function call), etc.

The change generally looks good to me, thanks.

[bryceberger]

Implementation (of non-function) aliases should be completed, feel free to review under that assumption.

Todo:

• docs
• tests