[PATCH 5/5] patch-id: tighten code to detect the patch header

[Junio C Hamano <gitster@pobox.com>]

The get_one_patchid() function unconditionally takes a line that
matches the patch header (namely, a line that begins with a full
object name, possibly prefixed by "commit" or "From" plus a space)
as the beginning of a patch.  Even when it is *not* looking for one
(namely, when the previous call found the patch header and returned,
and then we are called again to skip the log message and process the
patch whose header was found by the previous invocation).

As a consequence, a line in the commit log message that begins with
one of these patterns can be mistaken to start another patch, with
current message entirely skipped (because we haven't even reached
the patch at all).

Allow the caller to tell us if it called us already and saw the
patch header (in which case we shouldn't be looking for another one,
until we see the "diff" part of the patch; instead we simply should
be skipping these lines as part of the commit log message), and skip
the header processing logic when that is the case.  In the helper
function, it also needs to flip this "are we looking for a header?"
bit, once it finished skipping the commit log message and started
processing the patches, as the patch header of the _next_ message is
the only clue in the input that the current patch is done.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin/patch-id.c  | 43 ++++++++++++++++++++++++++++++-------------
 t/t4204-patch-id.sh | 17 +++++++++++++++++
 2 files changed, 47 insertions(+), 13 deletions(-)

diff --git a/builtin/patch-id.c b/builtin/patch-id.c
index a649966f31..0e6aab1ca2 100644
--- a/builtin/patch-id.c
+++ b/builtin/patch-id.c
@@ -60,12 +60,14 @@ static int scan_hunk_header(const char *p, int *p_before, int *p_after)
 
 #define GOPID_STABLE   01
 #define GOPID_VERBATIM 02
+#define GOPID_FIND_HEADER 04
 
 static int get_one_patchid(struct object_id *next_oid, struct object_id *result,
 			   struct strbuf *line_buf, unsigned flags)
 {
 	int stable = flags & GOPID_STABLE;
 	int verbatim = flags & GOPID_VERBATIM;
+	int find_header = flags & GOPID_FIND_HEADER;
 	int patchlen = 0, found_next = 0;
 	int before = -1, after = -1;
 	int diff_is_binary = 0;
@@ -81,26 +83,39 @@ static int get_one_patchid(struct object_id *next_oid, struct object_id *result,
 		int len;
 
 		/*
-		 * If we see a line that begins with "<object name>",
-		 * "commit <object name>" or "From <object name>", it is
-		 * the beginning of a patch.  Return to the caller, as
-		 * we are done with the one we have been processing.
+		 * The caller hasn't seen us find a patch header and
+		 * return to it, or we have started processing patch
+		 * and may encounter the beginning of the next patch.
 		 */
-		if (skip_prefix(line, "commit ", &p))
-			;
-		else if (skip_prefix(line, "From ", &p))
-			;
-		if (!get_oid_hex(p, next_oid)) {
-			if (verbatim)
-				the_hash_algo->update_fn(&ctx, line, strlen(line));
-			found_next = 1;
-			break;
+		if (find_header) {
+			/*
+			 * If we see a line that begins with "<object name>",
+			 * "commit <object name>" or "From <object name>", it is
+			 * the beginning of a patch.  Return to the caller, as
+			 * we are done with the one we have been processing.
+			 */
+			if (skip_prefix(line, "commit ", &p))
+				;
+			else if (skip_prefix(line, "From ", &p))
+				;
+			if (!get_oid_hex(p, next_oid)) {
+				if (verbatim)
+					the_hash_algo->update_fn(&ctx, line, strlen(line));
+				found_next = 1;
+				break;
+			}
 		}
 
 		/* Ignore commit comments */
 		if (!patchlen && !starts_with(line, "diff "))
 			continue;
 
+		/*
+		 * We are past the commit log message.  Prepare to
+		 * stop at the beginning of the next patch header.
+		 */
+		find_header = 1;
+
 		/* Parsing diff header?  */
 		if (before == -1) {
 			if (starts_with(line, "GIT binary patch") ||
@@ -196,11 +211,13 @@ static void generate_id_list(unsigned flags)
 	struct strbuf line_buf = STRBUF_INIT;
 
 	oidclr(&oid);
+	flags |= GOPID_FIND_HEADER;
 	while (!feof(stdin)) {
 		patchlen = get_one_patchid(&n, &result, &line_buf, flags);
 		if (patchlen)
 			flush_current_id(&oid, &result);
 		oidcpy(&oid, &n);
+		flags &= ~GOPID_FIND_HEADER;
 	}
 	strbuf_release(&line_buf);
 }
diff --git a/t/t4204-patch-id.sh b/t/t4204-patch-id.sh
index 1627fdda1b..b1d98d4110 100755
--- a/t/t4204-patch-id.sh
+++ b/t/t4204-patch-id.sh
@@ -137,6 +137,23 @@ test_expect_success 'patch-id computes the same for various formats' '
 	test_cmp actual expect
 '
 
+hash=$(git rev-parse same:)
+for cruft in "$hash" "commit $hash is bad" "From $hash status"
+do
+	test_expect_success "patch-id with <$cruft> in log message" '
+		git format-patch -1 --stdout same >patch-0 &&
+		git patch-id <patch-0 >expect &&
+
+		{
+			sed -e "/^$/q" patch-0 &&
+			printf "random message\n%s\n\n" "$cruft" &&
+			sed -e "1,/^$/d" patch-0
+		} >patch-cruft &&
+		git patch-id <patch-cruft >actual &&
+		test_cmp actual expect
+	'
+done
+
 test_expect_success 'whitespace is irrelevant in footer' '
 	get_patch_id main &&
 	git checkout same &&
-- 
2.45.2-786-g49444cbe9a