[PATCH v4 1/6] patch-id: fix stable patch id for binary / header-only

["Jerry Zhang via GitGitGadget" <gitgitgadget@gmail.com>]

From: Jerry Zhang <jerry@skydio.com>

Patch-ids for binary patches are found by hashing the object
ids of the before and after objects in succession. However in
the --stable case, there is a bug where hunks are not flushed
for binary and header-only patch ids, which would always result
in a patch-id of 0000. The --unstable case is currently correct.

Reorder the logic to branch into 3 cases for populating the
patch body: header-only which populates nothing, binary which
populates the object ids, and normal which populates the text
diff. All branches will end up flushing the hunk.

Don't populate the ---a/ and +++b/ lines for binary diffs, to correspond
to those lines not being present in the "git diff" text output.
This is necessary because we advertise that the patch-id calculated
internally and used in format-patch is the same that what the
builtin "git patch-id" would produce when piped from a diff.

Update the test to run on both binary and normal files.

Signed-off-by: Jerry Zhang <jerry@skydio.com>
---
 diff.c                     | 58 +++++++++++++++++++-------------------
 t/t3419-rebase-patch-id.sh | 34 +++++++++++++++-------
 2 files changed, 53 insertions(+), 39 deletions(-)

diff --git a/diff.c b/diff.c
index 648f6717a55..c15169e4b06 100644
--- a/diff.c
+++ b/diff.c
@@ -6253,46 +6253,46 @@ static int diff_get_patch_id(struct diff_options *options, struct object_id *oid
 		if (p->one->mode == 0) {
 			patch_id_add_string(&ctx, "newfilemode");
 			patch_id_add_mode(&ctx, p->two->mode);
-			patch_id_add_string(&ctx, "---/dev/null");
-			patch_id_add_string(&ctx, "+++b/");
-			the_hash_algo->update_fn(&ctx, p->two->path, len2);
 		} else if (p->two->mode == 0) {
 			patch_id_add_string(&ctx, "deletedfilemode");
 			patch_id_add_mode(&ctx, p->one->mode);
-			patch_id_add_string(&ctx, "---a/");
-			the_hash_algo->update_fn(&ctx, p->one->path, len1);
-			patch_id_add_string(&ctx, "+++/dev/null");
-		} else {
-			patch_id_add_string(&ctx, "---a/");
-			the_hash_algo->update_fn(&ctx, p->one->path, len1);
-			patch_id_add_string(&ctx, "+++b/");
-			the_hash_algo->update_fn(&ctx, p->two->path, len2);
 		}
 
-		if (diff_header_only)
-			continue;
-
-		if (fill_mmfile(options->repo, &mf1, p->one) < 0 ||
-		    fill_mmfile(options->repo, &mf2, p->two) < 0)
-			return error("unable to read files to diff");
-
-		if (diff_filespec_is_binary(options->repo, p->one) ||
+		if (diff_header_only) {
+			/* don't do anything since we're only populating header info */
+		} else if (diff_filespec_is_binary(options->repo, p->one) ||
 		    diff_filespec_is_binary(options->repo, p->two)) {
 			the_hash_algo->update_fn(&ctx, oid_to_hex(&p->one->oid),
 					the_hash_algo->hexsz);
 			the_hash_algo->update_fn(&ctx, oid_to_hex(&p->two->oid),
 					the_hash_algo->hexsz);
-			continue;
-		}
-
-		xpp.flags = 0;
-		xecfg.ctxlen = 3;
-		xecfg.flags = XDL_EMIT_NO_HUNK_HDR;
-		if (xdi_diff_outf(&mf1, &mf2, NULL,
-				  patch_id_consume, &data, &xpp, &xecfg))
-			return error("unable to generate patch-id diff for %s",
-				     p->one->path);
+		} else {
+			if (p->one->mode == 0) {
+				patch_id_add_string(&ctx, "---/dev/null");
+				patch_id_add_string(&ctx, "+++b/");
+				the_hash_algo->update_fn(&ctx, p->two->path, len2);
+			} else if (p->two->mode == 0) {
+				patch_id_add_string(&ctx, "---a/");
+				the_hash_algo->update_fn(&ctx, p->one->path, len1);
+				patch_id_add_string(&ctx, "+++/dev/null");
+			} else {
+				patch_id_add_string(&ctx, "---a/");
+				the_hash_algo->update_fn(&ctx, p->one->path, len1);
+				patch_id_add_string(&ctx, "+++b/");
+				the_hash_algo->update_fn(&ctx, p->two->path, len2);
+			}
 
+			if (fill_mmfile(options->repo, &mf1, p->one) < 0 ||
+			    fill_mmfile(options->repo, &mf2, p->two) < 0)
+				return error("unable to read files to diff");
+			xpp.flags = 0;
+			xecfg.ctxlen = 3;
+			xecfg.flags = XDL_EMIT_NO_HUNK_HDR;
+			if (xdi_diff_outf(&mf1, &mf2, NULL,
+					  patch_id_consume, &data, &xpp, &xecfg))
+				return error("unable to generate patch-id diff for %s",
+					     p->one->path);
+		}
 		if (stable)
 			flush_one_hunk(oid, &ctx);
 	}
diff --git a/t/t3419-rebase-patch-id.sh b/t/t3419-rebase-patch-id.sh
index 295040f2fe3..d24e55aac8d 100755
--- a/t/t3419-rebase-patch-id.sh
+++ b/t/t3419-rebase-patch-id.sh
@@ -43,15 +43,16 @@ test_expect_success 'setup: 500 lines' '
 	git add newfile &&
 	git commit -q -m "add small file" &&
 
-	git cherry-pick main >/dev/null 2>&1
-'
+	git cherry-pick main >/dev/null 2>&1 &&
 
-test_expect_success 'setup attributes' '
-	echo "file binary" >.gitattributes
+	git branch -f squashed main &&
+	git checkout -q -f squashed &&
+	git reset -q --soft HEAD~2 &&
+	git commit -q -m squashed
 '
 
 test_expect_success 'detect upstream patch' '
-	git checkout -q main &&
+	git checkout -q main^{} &&
 	scramble file &&
 	git add file &&
 	git commit -q -m "change big file again" &&
@@ -61,14 +62,27 @@ test_expect_success 'detect upstream patch' '
 	test_must_be_empty revs
 '
 
+test_expect_success 'detect upstream patch binary' '
+	echo "file binary" >.gitattributes &&
+	git checkout -q other^{} &&
+	git rebase main &&
+	git rev-list main...HEAD~ >revs &&
+	test_must_be_empty revs &&
+	test_when_finished "rm .gitattributes"
+'
+
 test_expect_success 'do not drop patch' '
-	git branch -f squashed main &&
-	git checkout -q -f squashed &&
-	git reset -q --soft HEAD~2 &&
-	git commit -q -m squashed &&
 	git checkout -q other^{} &&
 	test_must_fail git rebase squashed &&
-	git rebase --quit
+	test_when_finished "git rebase --abort"
+'
+
+test_expect_success 'do not drop patch binary' '
+	echo "file binary" >.gitattributes &&
+	git checkout -q other^{} &&
+	test_must_fail git rebase squashed &&
+	test_when_finished "git rebase --abort" &&
+	test_when_finished "rm .gitattributes"
 '
 
 test_done
-- 
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