Don’t append `--color=always` and `--sort-paths` unconditionally, since
`difftastic` doesn’t like repeated arguments, and the user might have
already set them (via `config.programs.difftastic.options`).
To clarify, if `difft` gets called with any parameter repeated, it will
croak:
difft --color=always --color=always
error: the argument '--color <WHEN>' cannot be used multiple times
Usage: difft [OPTIONS] OLD-PATH NEW-PATH
For more information, try '--help'.
By patching `cfg.options` we ensure that the parameters are defined, and
have the required value, since the user might have selected differently
for their general setup (again, via `config.programs.difftastic.options`).
The "dark" value actually applies to the `background` setting (which
I’ve omitted here since "dark" is its default value.)
I’ve given `color` the value "always", which will preserve colorization
when using `less` as a pager.
Extracted from `difft --help`¹:
Options:
...
--color <WHEN>
When to use color output.
[env: DFT_COLOR=]
[default: auto]
[possible values: always, auto, never]
--background <BACKGROUND>
Set the background brightness. Difftastic will prefer brighter colours on dark backgrounds.
[env: DFT_BACKGROUND=]
[default: dark]
[possible values: dark, light]
¹: which seems to be the authoritative source of documentation, as per
https://difftastic.wilfred.me.uk/usage.html#configuration-options
