programs.git.difftastic: Add support for configuring as difftool

[lilyball]

Description

Difftastic has documentation on configuring it as a difftool. It would be great if home-manager had a programs.git.difftastic.enableDifftool option that set up the difftool config, so I could set that instead of programs.git.difftool.enable if I'm already using a conflicting tool (like delta).

According to the linked documentation, the difftool config looks like

[diff]
        tool = difftastic

[difftool]
        prompt = false

[difftool "difftastic"]
        cmd = difft "$LOCAL" "$REMOTE"

In this case, the config option should just set the difftool.difftastic.cmd config (such that git difftool -t difftastic works). The others can be configured separately by the user as desired.

The primary use-case of this option is to allow the existing programs.git.difftastic options to apply to the newly-configured difftool.

Alternatives considered

The option here could be called programs.git.difftool.difftastic.enable instead, but that makes it less obvious that the programs.git.difftastic options would apply.

programs.git.difftastic could gain a read-only option cmd that contains the command string, thus allowing users to set programs.git.extraConfig.difftool.difftastic.cmd = config.programs.git.difftastic.cmd, though this feels awkward and harder to document.

An option programs.git.difftool could be added that's an enum that currently just allows the string "difftastic", which would not only set programs.git.difftastic.enableDifftool to true but would also set the diff.tool and difftool.prompt configs, along with pager.difftool = true as recommended by the linked documentation. It might also want to default core.pager to the same value that programs.git.difftastic.enable sets.

Maintainers

@rycee

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[pcasaretto]

I see we have programs.git.difftastic.enable. Should this be closed?

[thecaralice]

I see we have programs.git.difftastic.enable. Should this be closed?

No. The issue is with programs.git.difftastic.enable conflicting with programs.git.delta.enable which was not fixed. Neither does programs.git have any special things for difftool options.