Re: [PATCH v2 2/3] diff: add -I<regex> that ignores matching changes

> Add a new diff option that enables ignoring changes whose all lines
> (changed, removed, and added) match a given regular expression.  This is
> similar to the -I option in standalone diff utilities and can be used
> e.g. to ignore changes which only affect code comments or to look for
> unrelated changes in commits containing a large number of automatically
> applied modifications (e.g. a tree-wide string replacement).  The
> difference between -G/-S and the new -I option is that the latter
> filters output on a per-change basis.
>
> Use the 'ignore' field of xdchange_t for marking a change as ignored or
> not.  Since the same field is used by --ignore-blank-lines, identical
> hunk emitting rules apply for --ignore-blank-lines and -I.  These two
> options can also be used together in the same git invocation (they are
> complementary to each other).
>
> Rename xdl_mark_ignorable() to xdl_mark_ignorable_lines(), to indicate
> that it is logically a "sibling" of xdl_mark_ignorable_regex() rather
> than its "parent".
>
> Signed-off-by: Michał Kępień <michal@isc.org>

> +	Ignore changes whose all lines match <regex>.  This option may
> +	be specified more than once.
> +
>  --inter-hunk-context=<lines>::
>  	Show the context between diff hunks, up to the specified number
>  	of lines, thereby fusing hunks that are close to each other.
> diff --git a/diff.c b/diff.c
> index 2bb2f8f57e..c5d4920fee 100644
> --- a/diff.c
> +++ b/diff.c
> @@ -3587,6 +3587,8 @@ static void builtin_diff(const char *name_a,
>  		if (header.len && !o->flags.suppress_diff_headers)
>  			ecbdata.header = &header;
>  		xpp.flags = o->xdl_opts;
> +		xpp.ignore_regex = o->ignore_regex;
> +		xpp.ignore_regex_nr = o->ignore_regex_nr;
>  		xpp.anchors = o->anchors;
>  		xpp.anchors_nr = o->anchors_nr;
>  		xecfg.ctxlen = o->context;
> @@ -3716,6 +3718,8 @@ static void builtin_diffstat(const char *name_a, const char *name_b,
>  		memset(&xpp, 0, sizeof(xpp));
>  		memset(&xecfg, 0, sizeof(xecfg));
>  		xpp.flags = o->xdl_opts;
> +		xpp.ignore_regex = o->ignore_regex;
> +		xpp.ignore_regex_nr = o->ignore_regex_nr;
>  		xpp.anchors = o->anchors;
>  		xpp.anchors_nr = o->anchors_nr;
>  		xecfg.ctxlen = o->context;
> @@ -5203,6 +5207,22 @@ static int diff_opt_patience(const struct option *opt,
>  	return 0;
>  }
>  
> +static int diff_opt_ignore_regex(const struct option *opt,
> +				 const char *arg, int unset)
> +{
> +	struct diff_options *options = opt->value;
> +	regex_t *regex;
> +
> +	BUG_ON_OPT_NEG(unset);
> +	regex = xcalloc(1, sizeof(*regex));
> +	if (regcomp(regex, arg, REG_EXTENDED | REG_NEWLINE))
> +		die("invalid regex: %s", arg);
> +	ALLOC_GROW(options->ignore_regex, options->ignore_regex_nr + 1,
> +		   options->ignore_regex_alloc);
> +	options->ignore_regex[options->ignore_regex_nr++] = regex;
> +	return 0;
> +}