diff: fix "multiple regexp" semantics to find hunk header comment

When multiple regular expressions are concatenated with "\n", they were
traditionally AND'ed together, and only a line that matches _all_ of them
is taken as a match.  This however is unwieldy when multiple regexp
feature is used to specify alternatives.

This fixes the semantics to take the first match.  A nagative pattern, if
matches, makes the line to fail as before.  A match with a positive
pattern will be the final match, and what it captures in $1 is used as the
hunk header comment.

We could write alternatives using "|" in ERE, but the machinery can only
use captured $1 as the hunk header comment (or $0 if there is no match in
$1), so you cannot write:

    "junk ( A | B ) | garbage ( C | D )"

and expect both "junk" and "garbage" to get stripped with the existing
code.  With this fix, you can write it as:

    "junk ( A | B ) \n garbage ( C | D )"

and the way capture works would match the user expectation more
naturally.

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

1 files changed, 10 insertions, 7 deletions

diff --git a/xdiff-interface.c b/xdiff-interface.c
index 7f1a7d3ffc..6c6bb19973 100644
--- a/xdiff-interface.c
+++ b/xdiff-interface.c
@@ -194,26 +194,29 @@ static long ff_regexp(const char *line, long len,
 	char *line_buffer = xstrndup(line, len); /* make NUL terminated */
 	struct ff_regs *regs = priv;
 	regmatch_t pmatch[2];
-	int result = 0, i;
+	int i;
+	int result = -1;
 
 	for (i = 0; i < regs->nr; i++) {
 		struct ff_reg *reg = regs->array + i;
-		if (reg->negate ^ !!regexec(&reg->re,
-					line_buffer, 2, pmatch, 0)) {
-			free(line_buffer);
-			return -1;
+		if (!regexec(&reg->re, line_buffer, 2, pmatch, 0)) {
+			if (reg->negate)
+				goto fail;
+			break;
 		}
 	}
+	if (regs->nr <= i)
+		goto fail;
 	i = pmatch[1].rm_so >= 0 ? 1 : 0;
 	line += pmatch[i].rm_so;
 	result = pmatch[i].rm_eo - pmatch[i].rm_so;
 	if (result > buffer_size)
 		result = buffer_size;
 	else
-		while (result > 0 && (isspace(line[result - 1]) ||
-					line[result - 1] == '\n'))
+		while (result > 0 && (isspace(line[result - 1])))
 			result--;
 	memcpy(buffer, line, result);
+ fail:
 	free(line_buffer);
 	return result;
 }