[PATCH v2 2/2] cat-file: add mailmap support to --batch-check option

[Siddharth Asthana <siddharthasthana31@gmail.com>]

Even though the cat-file command with `--batch-check` option does not
complain when `--use-mailmap` option is given, the latter option is
ignored. Compute the size of the object after replacing the idents and
report it instead.

In order to make `--batch-check` option honour the mailmap mechanism we
have to read the contents of the commit/tag object.

There were two ways to do it:

1. Make two calls to `oid_object_info_extended()`. If `--use-mailmap`
   option is given, the first call will get us the type of the object
   and second call will only be made if the object type is either a
   commit or tag to get the contents of the object.

2. Make one call to `oid_object_info_extended()` to get the type of the
   object. Then, if the object type is either of commit or tag, make a
   call to `read_object_file()` to read the contents of the object.

I benchmarked the following command with both the above approaches and
compared against the current implementation where `--use-mailmap`
option is ignored:

`git cat-file --use-mailmap --batch-all-objects --batch-check --buffer
--unordered`

The results can be summarized as follows:
                       Time (mean ± σ)
default               827.7 ms ± 104.8 ms
first approach        6.197 s ± 0.093 s
second approach       1.975 s ± 0.217 s

Since, the second approach is faster than the first one, I implemented
it in this patch.

Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: John Cai <johncai86@gmail.com>
Signed-off-by: Siddharth Asthana <siddharthasthana31@gmail.com>
---
 Documentation/git-cat-file.txt |  2 ++
 builtin/cat-file.c             | 14 ++++++++++++++
 t/t4203-mailmap.sh             | 22 ++++++++++++++++++++++
 3 files changed, 38 insertions(+)

diff --git a/Documentation/git-cat-file.txt b/Documentation/git-cat-file.txt
index 594b6f2dfd..a8e7906b3d 100644
--- a/Documentation/git-cat-file.txt
+++ b/Documentation/git-cat-file.txt
@@ -103,6 +103,8 @@ OPTIONS
 	`--textconv` or `--filters`, in which case the input lines also
 	need to specify the path, separated by whitespace.  See the
 	section `BATCH OUTPUT` below for details.
+	If used with `--use-mailmap` option, will show the size of
+	updated object after replacing idents using the mailmap mechanism.
 
 --batch-command::
 --batch-command=<format>::
diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index 9942b93867..7ee8cb453f 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -444,6 +444,9 @@ static void batch_object_write(const char *obj_name,
 	if (!data->skip_object_info) {
 		int ret;
 
+		if (use_mailmap)
+			data->info.typep = &data->type;
+
 		if (pack)
 			ret = packed_object_info(the_repository, pack, offset,
 						 &data->info);
@@ -457,6 +460,17 @@ static void batch_object_write(const char *obj_name,
 			fflush(stdout);
 			return;
 		}
+
+		if (use_mailmap && (data->type == OBJ_COMMIT || data->type == OBJ_TAG)) {
+			size_t s = data->size;
+			char *buf = NULL;
+
+			buf = read_object_file(&data->oid, &data->type, &data->size);
+			buf = replace_idents_using_mailmap(buf, &s);
+			data->size = cast_size_t_to_ulong(s);
+
+			free(buf);
+		}
 	}
 
 	strbuf_reset(scratch);
diff --git a/t/t4203-mailmap.sh b/t/t4203-mailmap.sh
index 59513e7c57..4b236c68aa 100755
--- a/t/t4203-mailmap.sh
+++ b/t/t4203-mailmap.sh
@@ -1032,4 +1032,26 @@ test_expect_success 'git cat-file -s returns correct size with --use-mailmap' '
 	test_cmp expect actual
 '
 
+test_expect_success 'git cat-file --batch-check returns correct size with --use-mailmap' '
+	test_when_finished "rm .mailmap" &&
+	cat >.mailmap <<-EOF &&
+	C O Mitter <committer@example.com> Orig <orig@example.com>
+	EOF
+	echo "92d99959b011b1cd69fe7be5315d6732fe302575 commit 220" >expect &&
+	echo "HEAD" >in &&
+	git cat-file --use-mailmap --batch-check <in >actual &&
+	test_cmp expect actual
+'
+
+test_expect_success 'git cat-file --batch-command returns correct size with --use-mailmap' '
+	test_when_finished "rm .mailmap" &&
+	cat >.mailmap <<-EOF &&
+	C O Mitter <committer@example.com> Orig <orig@example.com>
+	EOF
+	echo "92d99959b011b1cd69fe7be5315d6732fe302575 commit 220" >expect &&
+	echo "info HEAD" >in &&
+	git cat-file --use-mailmap --batch-command <in >actual &&
+	test_cmp expect actual
+'
+
 test_done
-- 
2.38.0.rc1.8.g9592ff2ba4