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[PATCH v2] grep: provide sane default to grep_source struct

grep_buffer creates a struct grep_source gs and calls grep_source()
with it. However, gs.name is null, which eventually produces a
segmentation fault in
grep_source()->grep_source_1()->show_line() when grep_opt.status_only is
not set.

This seems to be unreachable from existing commands but is reachable in
the event that someone rolls their own revision walk and neglects to set
rev_info->grep_filter->status_only. Conceivably, someone might want to
print all changed lines of all commits which match some regex.

To futureproof, give developers a heads-up if grep_source() is called
and a valid name field is expected but not given. This path should be
unreachable now, but in the future may become reachable if developers
want to add the ability to use grep_buffer() in prepared in-core data
and provide hints to the user about where the data came from.

Signed-off-by: Emily Shaffer <emilyshaffer@xxxxxxxxxx>
I've added the BUG() line to grep_source(). I considered adding it to
grep_source_1() but didn't see much difference. Looks like
grep_source_1() exists purely as a helper to grep_source() and is never
called by anybody else... but it's the function where the crash would
happen. So I'm not sure.

I also modified the wording for the BUG("") statement a little from
jrn's suggestion to hopefully make it more explicit, but I welcome

 grep.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/grep.c b/grep.c
index 0d50598acd..6ceb880a8c 100644
--- a/grep.c
+++ b/grep.c
@@ -2021,6 +2021,9 @@ static int chk_hit_marker(struct grep_expr *x)
 int grep_source(struct grep_opt *opt, struct grep_source *gs)
+	if (!opt->status_only && gs->name == NULL)
+		BUG("grep call which could print a name requires "
+		    "grep_source.name be non-NULL");
 	 * we do not have to do the two-pass grep when we do not check
 	 * buffer-wide "all-match".
@@ -2045,7 +2048,11 @@ int grep_buffer(struct grep_opt *opt, char *buf, unsigned long size)
 	struct grep_source gs;
 	int r;
-	grep_source_init(&gs, GREP_SOURCE_BUF, NULL, NULL, NULL);
+	/* TODO: In the future it may become desirable to pass in the name as
+	 * an argument to grep_buffer(). At that time, "(in core)" should be
+	 * replaced.
+	 */
+	grep_source_init(&gs, GREP_SOURCE_BUF, _("(in core)"), NULL, NULL);
 	gs.buf = buf;
 	gs.size = size;