Subject: [PATCH 25/25] pickaxe -G: terminate early on matching lines

From: Ævar Arnfjörð Bjarmason <[email-masked]>
Date: Wed, 3 Feb 2021 04:28:11 +0100

Solve a long-standing item for "git log -Grx" of us e.g. finding "+
str" in the diff context and noting that we had a "hit", but xdiff
diligently continuing to generate and spew the rest of the diff at us.

The TODO item has been there since "git log -G" was implemented. See
f506b8e8b5f (git log/diff: add -G<regexp> that greps in the patch
text, 2010-08-23).

Our xdiff interface also had the limitation of not being able to abort
early since the beginning, see d9ea73e0564 (combine-diff: refactor
built-in xdiff interface., 2006-04-05). Although at that time
"xdiff_emit_line_fn" was called "xdiff_emit_consume_fn", and
"xdiff_emit_hunk_fn" didn't exist yet.

But now with the support added in the preceding ""xdiff-interface:
allow early return from xdiff_emit_{line,hunk}_fn" commit we can
return early, and furthermore test the functionality of the new
early-exit xdiff-interface by having a BUG() call here to die if it
ever starts handing us needless work again.

Signed-off-by: Ævar Arnfjörð Bjarmason <[email-masked]>
---
 diffcore-pickaxe.c | 29 +++++++++++++++++++----------
 xdiff-interface.h  |  5 +++++
 2 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/diffcore-pickaxe.c b/diffcore-pickaxe.c
index 21f9d66b6a..e773fa69a2 100644
--- a/diffcore-pickaxe.c
+++ b/diffcore-pickaxe.c
@@ -29,12 +29,11 @@ static int diffgrep_consume(void *priv, char *line, unsigned long len)
 	if (line[0] != '+' && line[0] != '-')
 		return 0;
 	if (data->hit)
-		/*
-		 * NEEDSWORK: we should have a way to terminate the
-		 * caller early.
-		 */
-		return 0;
-	data->hit = patmatch(grep_pat, line + 1, line + len + 1, &regmatch, 0);
+		BUG("Already matched in diffgrep_consume! Broken xdiff_emit_line_fn?");
+	if (patmatch(grep_pat, line + 1, line + len + 1, &regmatch, 0)) {
+		data->hit = 1;
+		return -1;
+	}
 	return 0;
 }
 
@@ -47,6 +46,7 @@ static int diff_grep(mmfile_t *one, mmfile_t *two,
 	xdemitconf_t xecfg;
 	regmatch_t regmatch;
 	struct grep_pat *grep_pat = grep_filter->pattern_list;
+	int ret;
 
 	if (!one)
 		return patmatch(grep_pat, two->ptr, two->ptr + two->size,
@@ -65,10 +65,19 @@ static int diff_grep(mmfile_t *one, mmfile_t *two,
 	ecbdata.hit = 0;
 	xecfg.ctxlen = 0;
 	xecfg.interhunkctxlen = o->interhunkcontext;
-	if (xdi_diff_outf(one, two, discard_hunk_line, diffgrep_consume,
-			  &ecbdata, &xpp, &xecfg))
-		return 0;
-	return ecbdata.hit;
+
+	/*
+	 * An xdiff error might be our "data->hit" from above. See the
+	 * comment for xdiff_emit_{line,hunk}_fn in xdiff-interface.h
+	 * for why.
+	 */
+	ret = xdi_diff_outf(one, two, discard_hunk_line, diffgrep_consume,
+			    &ecbdata, &xpp, &xecfg);
+	if (ecbdata.hit)
+		return 1;
+	if (ret)
+		return ret;
+	return 0;
 }
 
 static unsigned int contains(mmfile_t *mf, struct grep_opt *grep_filter)
diff --git a/xdiff-interface.h b/xdiff-interface.h
index 1b27d6104c..347d8a4425 100644
--- a/xdiff-interface.h
+++ b/xdiff-interface.h
@@ -25,6 +25,11 @@
  * granular return values, but for now use it carefully, or consider
  * e.g. using discard_hunk_line() if you say just don't care about
  * hunk headers.
+ *
+ * Note that just returning -1 will make your early return
+ * indistinguishable from an error internal to xdiff. See "diff_grep"
+ * in diffcore-pickaxe.c for a trick to work around this, i.e. using
+ * the "consume_callback_data" to note the desired early return.
  */
 typedef int (*xdiff_emit_line_fn)(void *, char *, unsigned long);
 typedef int (*xdiff_emit_hunk_fn)(void *data,
-- 
2.30.0.284.gd98b1dd5eaa7