patchpull: do not warn when opt_ff is explicitly specified

> If the warning is silenced by specifying `pull.ff = "only"`, as
> instructed, the warning will arise again if the user runs
> something like `git pull --no-ff`. However, the warning should not
> happen as the user clearly knows what they're doing.
>
> Don't display the warning if opt_ff is explicitly set by a command-line
> option given by a user.
>
> Signed-off-by: Denton Liu <liu.denton@gmail.com>
> ---
>  builtin/pull.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/builtin/pull.c b/builtin/pull.c
> index 015f6ded0b..307b4b5d21 100644
> --- a/builtin/pull.c
> +++ b/builtin/pull.c
> @@ -83,6 +83,7 @@ static char *opt_commit;
>  static char *opt_edit;
>  static char *cleanup_arg;
>  static char *opt_ff;
> +static int opt_ff_explicit;
>  static char *opt_verify_signatures;
>  static int opt_autostash = -1;
>  static int config_autostash;
> @@ -344,7 +345,7 @@ static enum rebase_type config_get_rebase(void)
>  	if (!git_config_get_value("pull.rebase", &value))
>  		return parse_config_rebase("pull.rebase", value, 1);
>  
> -	if (opt_verbosity >= 0 &&
> +	if (!opt_ff_explicit && opt_verbosity >= 0 &&
>  	    (!opt_ff || strcmp(opt_ff, "--ff-only"))) {
>  		warning(_("Pulling without specifying how to reconcile divergent branches is\n"
>  			"discouraged. You can squelch this message by running one of the following\n"
> @@ -933,6 +934,8 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
>  
>  	if (!opt_ff)
>  		opt_ff = xstrdup_or_null(config_get_ff());
> +	else
> +		opt_ff_explicit = 1;
>  
>  	if (opt_rebase < 0)
>  		opt_rebase = config_get_rebase();

>
> In d18c950a69 (pull: warn if the user didn't say whether to rebase or to
> merge, 2020-03-09), `git pull` was taught to warn users if they
> have `pull.rebase` unset or `pull.ff != "only"`. However, this warning
> is a little too eager about happening.
>
> If the warning is silenced by specifying `pull.ff = "only"`, as
> instructed, the warning will arise again if the user runs
> something like `git pull --no-ff`. However, the warning should not
> happen as the user clearly knows what they're doing.
>
> Don't display the warning if opt_ff is explicitly set by a command-line
> option given by a user.

>
> Hi Denton, thanks for working on this! We can also assume that the
> user knows what they are doing and does not need a warning if they
> have run `git config --global pull.ff no`. So really, we can just get
> rid of the check for strcmp(opt_ff, "--ff-only") altogether and
> instead only check !opt_ff. Could you do that and add some more tests
> to t5521-pull-options.sh?