Re: [PATCH 5/5] grep: remove regflags from the public grep_opt API

> Refactor calls to the grep machinery to always pass opt.ignore_case &
> opt.extended_regexp_option instead of setting the equivalent regflags
> bits.
>
> The bug fixed when making -i work with -P in commit 9e3cbc59d5 ("log:
> make --regexp-ignore-case work with --perl-regexp", 2017-05-20) was
> really just plastering over the code smell which this change fixes.
>
> See my "Re: [PATCH v3 05/30] log: make --regexp-ignore-case work with
> --perl-regexp"[1] for the discussion leading up to this.
>
> The reason for adding the extensive commentary here is that I
> discovered some subtle complexity in implementing this that really
> should be called out explicitly to future readers.
>
> Before this change we'd rely on the difference between
> `extended_regexp_option` and `regflags` to serve as a membrane between
> our preliminary parsing of grep.extendedRegexp and grep.patternType,
> and what we decided to do internally.
>
> Now that those two are the same thing, it's necessary to unset
> `extended_regexp_option` just before we commit in cases where both of
> those config variables are set. See 84befcd0a4 ("grep: add a
> grep.patternType configuration setting", 2012-08-03) for the code and
> documentation related to that.
>
> The explanation of why the if/else branches in
> grep_commit_pattern_type() are ordered the way they are exists in that
> commit message, but I think it's worth calling this subtlety out
> explicitly with a comment for future readers.

>
> Unrelated to that: I could have factored out the default REG_NEWLINE
> flag into some custom GIT_GREP_H_DEFAULT_REGFLAGS or something, but
> since it's just used in two places I didn't think it was worth the
> effort.
>
> As an aside we're really lacking test coverage regflags being
> initiated as 0 instead of as REG_NEWLINE. Tests will fail if it's
> removed from compile_regexp(), but not if it's removed from
> compile_fixed_regexp(). I have not dug to see if it's actually needed
> in the latter case or if the test coverage is lacking.

>
> 1. <CACBZZX6Hp4Q4TOj_X1fbdCA4twoXF5JemZ5ZbEn7wmkA=1KO2g@mail.gmail.com>
>    (https://public-inbox.org/git/CACBZZX6Hp4Q4TOj_X1fbdCA4twoXF5JemZ5ZbEn7wmkA=1KO2g@mail.gmail.com/)
>
> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> ---
>  builtin/grep.c |  2 --
>  grep.c         | 43 ++++++++++++++++++++++++++++++++++---------
>  grep.h         |  1 -
>  revision.c     |  2 --
>  4 files changed, 34 insertions(+), 14 deletions(-)
>
> diff --git a/builtin/grep.c b/builtin/grep.c
> index f61a9d938b..b682966439 100644
> --- a/builtin/grep.c
> +++ b/builtin/grep.c
> @@ -1169,8 +1169,6 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
>
>         if (!opt.pattern_list)
>                 die(_("no pattern given."));
> -       if (!opt.fixed && opt.ignore_case)
> -               opt.regflags |= REG_ICASE;
>
>         /*
>          * We have to find "--" in a separate pass, because its presence
> diff --git a/grep.c b/grep.c
> index 736e1e00d6..51aaad9f03 100644
> --- a/grep.c
> +++ b/grep.c
> @@ -35,7 +35,6 @@ void init_grep_defaults(void)
>         memset(opt, 0, sizeof(*opt));
>         opt->relative = 1;
>         opt->pathname = 1;
> -       opt->regflags = REG_NEWLINE;
>         opt->max_depth = -1;
>         opt->pattern_type_option = GREP_PATTERN_TYPE_UNSPECIFIED;
>         color_set(opt->color_context, "");
> @@ -154,7 +153,6 @@ void grep_init(struct grep_opt *opt, const char *prefix)
>         opt->linenum = def->linenum;
>         opt->max_depth = def->max_depth;
>         opt->pathname = def->pathname;
> -       opt->regflags = def->regflags;
>         opt->relative = def->relative;
>         opt->output = def->output;
>
> @@ -170,6 +168,24 @@ void grep_init(struct grep_opt *opt, const char *prefix)
>
>  static void grep_set_pattern_type_option(enum grep_pattern_type pattern_type, struct grep_opt *opt)
>  {
> +       /*
> +        * When committing to the pattern type by setting the relevant
> +        * fields in grep_opt it's generally not necessary to zero out
> +        * the fields we're not choosing, since they won't have been
> +        * set by anything. The extended_regexp_option field is the
> +        * only exception to this.
> +        *
> +        * This is because in the process of parsing grep.patternType
> +        * & grep.extendedRegexp we set opt->pattern_type_option and
> +        * opt->extended_regexp_option, respectively. We then
> +        * internally use opt->extended_regexp_option to see if we're
> +        * compiling an ERE. It must be unset if that's not actually
> +        * the case.
> +        */
> +       if (pattern_type != GREP_PATTERN_TYPE_ERE &&
> +           opt->extended_regexp_option)
> +               opt->extended_regexp_option = 0;
> +
>         switch (pattern_type) {
>         case GREP_PATTERN_TYPE_UNSPECIFIED:
>                 /* fall through */
> @@ -178,7 +194,7 @@ static void grep_set_pattern_type_option(enum grep_pattern_type pattern_type, st
>                 break;
>
>         case GREP_PATTERN_TYPE_ERE:
> -               opt->regflags |= REG_EXTENDED;
> +               opt->extended_regexp_option = 1;
>                 break;
>
>         case GREP_PATTERN_TYPE_FIXED:
> @@ -208,6 +224,11 @@ void grep_commit_pattern_type(enum grep_pattern_type pattern_type, struct grep_o
>         else if (opt->pattern_type_option != GREP_PATTERN_TYPE_UNSPECIFIED)
>                 grep_set_pattern_type_option(opt->pattern_type_option, opt);
>         else if (opt->extended_regexp_option)
> +               /*
> +                * This branch *must* happen after setting from the
> +                * opt->pattern_type_option above,