Re: [PATCH 3/4] add-interactive: manually fall back color config to color.ui

[Patrick Steinhardt <ps@pks.im>]

On Thu, Aug 21, 2025 at 03:22:24AM -0400, Jeff King wrote:
> Color options like color.interactive and color.diff should fall back to
> the value of color.ui if they aren't set. In add-interactive, we check
> the specific options (e.g., color.diff) via repo_config_get_value(),
> which does not depend on the main command having loaded any color config
> via the git_config() callback mechanism.
> 
> But then we call want_color() on the result; if our specific config is
> unset then that function uses the value of git_use_color_default. That
> variable is typically set from color.ui by the git_color_config()
> callback, which is called by the main command in its own git_config()
> callback function.
> 
> This works fine for "add -p", whose add_config() callback calls into
> git_color_config(). But it doesn't work for other commands like
> "checkout -p", which is otherwise unaware of color at all. People tend
> not to notice because the default is "auto", and that's what they'd set
> color.ui to as well. But something like:
> 
>   git -c color.ui=false checkout -p
> 
> should disable color, and it doesn't.
> 
> This regression goes back to 0527ccb1b5 (add -i: default to the built-in
> implementation, 2021-11-30). In the perl version we got the color config
> from "git config --get-colorbool", which did the full lookup for us.
> 
> The obvious fix is for git-checkout to add a call to git_color_config()
> to its own config callback. But we'd have to do so for every command
> with this problem, which is error-prone. Let's see if we can fix it more
> centrally.
> 
> It is tempting to teach want_color() to look up the value of
> repo_config_get_value("color.ui") itself. But I think that would have
> disastrous consequences. Plumbing commands, especially older ones, avoid
> porcelain config like color. by simply not parsing it in their config

Is the "color." intended to refer to config keys starting with that
string? If so it would help to quote it and maybe say "color.*".

> diff --git a/add-interactive.c b/add-interactive.c
> index 95ab251963..db7e6a81a8 100644
> --- a/add-interactive.c
> +++ b/add-interactive.c
> @@ -45,6 +45,15 @@ static int check_color_config(struct repository *r, const char *var)
>  		ret = -1;
>  	else
>  		ret = git_config_colorbool(var, value);
> +
> +	/*
> +	 * Do not rely on want_color() to fall back to color.ui for us. It uses
> +	 * the value parsed by git_color_config(), which may not have been
> +	 * called by the main command.
> +	 */
> +	if (ret < 0 && !repo_config_get_value(r, "color.ui", &value))
> +		ret = git_config_colorbool("color.ui", value);

With the previous comments where I say that we should use
`GIT_COLOR_UNKNOWN` we should probably convert the `ret < 0` to `ret ==
GIT_COLOR_UNKNOWN`, as well.

> diff --git a/t/t3701-add-interactive.sh b/t/t3701-add-interactive.sh
> index 3f9cb9453f..0024991257 100755
> --- a/t/t3701-add-interactive.sh
> +++ b/t/t3701-add-interactive.sh
> @@ -1335,6 +1341,15 @@ do
>  		test_must_fail git $cmd --inter-hunk-context 2 2>actual &&
>  		test_grep -E ".--inter-hunk-context. requires .(--interactive/)?--patch." actual
>  	'
> +
> +	test_expect_success "$cmd falls back to color.ui" '
> +		git reset --hard patch-base &&
> +		echo working-tree >file &&
> +		test_write_lines y |
> +		force_color git -c color.ui=false $cmd -p >output.raw 2>&1 &&
> +		test_decode_color <output.raw >output &&
> +		test_cmp output.raw output
> +	'

Nice and straight-forward.

Patrick