git log/diff: add -G<regexp> that greps in the patch text

Teach "-G<regexp>" that is similar to "-S<regexp> --pickaxe-regexp" to the
"git diff" family of commands.  This limits the diff queue to filepairs
whose patch text actually has an added or a deleted line that matches the
given regexp.  Unlike "-S<regexp>", changing other parts of the line that
has a substring that matches the given regexp IS counted as a change, as
such a change would appear as one deletion followed by one addition in a
patch text.

Unlike -S (pickaxe) that is intended to be used to quickly detect a commit
that changes the number of occurrences of hits between the preimage and
the postimage to serve as a part of larger toolchain, this is meant to be
used as the top-level Porcelain feature.

The implementation unfortunately has to run "diff" twice if you are
running "log" family of commands to produce patches in the final output
(e.g. "git log -p" or "git format-patch").  I think we _could_ cache the
result in-core if we wanted to, but that would require larger surgery to
the diffcore machinery (i.e. adding an extra pointer in the filepair
structure to keep a pointer to a strbuf around, stuff the textual diff to
the strbuf inside diffgrep_consume(), and make use of it in later stages
when it is available) and it may not be worth it.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 7 insertions, 2 deletions

diff --git a/diff.c b/diff.c
index 6631fa387c..9095be16f6 100644
--- a/diff.c
+++ b/diff.c
@@ -3268,12 +3268,17 @@ int diff_opt_parse(struct diff_options *options, const char **av, int ac)
 	}
 	else if ((argcount = short_opt('S', av, &optarg))) {
 		options->pickaxe = optarg;
+		options->pickaxe_opts |= DIFF_PICKAXE_KIND_S;
+		return argcount;
+	} else if ((argcount = short_opt('G', av, &optarg))) {
+		options->pickaxe = optarg;
+		options->pickaxe_opts |= DIFF_PICKAXE_KIND_G;
 		return argcount;
 	}
 	else if (!strcmp(arg, "--pickaxe-all"))
-		options->pickaxe_opts = DIFF_PICKAXE_ALL;
+		options->pickaxe_opts |= DIFF_PICKAXE_ALL;
 	else if (!strcmp(arg, "--pickaxe-regex"))
-		options->pickaxe_opts = DIFF_PICKAXE_REGEX;
+		options->pickaxe_opts |= DIFF_PICKAXE_REGEX;
 	else if ((argcount = short_opt('O', av, &optarg))) {
 		options->orderfile = optarg;
 		return argcount;