On musl libc, ISO-2022-JP encoder is too eager to switch back to
1 byte encoding, musl's iconv always switch back after every combining
character. Comparing glibc and musl's output for this command
$ sed q t/t3900/ISO-2022-JP.txt| iconv -f ISO-2022-JP -t utf-8 |
	iconv -f utf-8 -t ISO-2022-JP | xxd

glibc:
00000000: 1b24 4224 4f24 6c24 5224 5b24 551b 2842  .$B$O$l$R$[$U.(B
00000010: 0a                                       .

musl:
00000000: 1b24 4224 4f1b 2842 1b24 4224 6c1b 2842  .$B$O.(B.$B$l.(B
00000010: 1b24 4224 521b 2842 1b24 4224 5b1b 2842  .$B$R.(B.$B$[.(B
00000020: 1b24 4224 551b 2842 0a                   .$B$U.(B.

Although musl iconv's output isn't optimal, it's still correct.

From commit 7d509878b8, ("pretty.c: format string with truncate respects
logOutputEncoding", 2014-05-21), we're encoding the message to utf-8
first, then format it and convert the message to the actual output
encoding on git commit --squash.

Thus, t3900 is failing on Linux with musl libc.

Reencode to utf-8 before arranging rebase's todo list.

Signed-off-by: Doan Tran Cong Danh <redacted>
---

Notes:
    The todo list shown to user has already been reencoded by sequencer_make_script,
    without this patch it looks like this:
    
    $ head -3 .git/rebase-merge/git-rebase-todo | xxd
    00000000: 7069 636b 2065 6633 3961 3033 201b 2442  pick ef39a03 .$B
    00000010: 244f 1b28 421b 2442 246c 1b28 421b 2442  $O.(B.$B$l.(B.$B
    00000020: 2452 1b28 421b 2442 245b 1b28 421b 2442  $R.(B.$B$[.(B.$B
    00000030: 2455 1b28 420a 7069 636b 2062 3832 3931  $U.(B.pick b8291
    00000040: 3336 2073 7175 6173 6821 201b 2442 244f  36 squash! .$B$O
    00000050: 1b28 421b 2442 246c 1b28 421b 2442 2452  .(B.$B$l.(B.$B$R
    00000060: 1b28 421b 2442 245b 1b28 421b 2442 2455  .(B.$B$[.(B.$B$U
    00000070: 1b28 420a 7069 636b 2062 3532 3132 6437  .(B.pick b5212d7
    00000080: 2069 6e74 6572 6d65 6469 6174 6520 636f   intermediate co
    00000090: 6d6d 6974 0a                             mmit.

 sequencer.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sequencer.c b/sequencer.c
index 9d5964fd81..69430fe23f 100644
--- a/sequencer.c
+++ b/sequencer.c

@@ -5169,7 +5169,7 @@ int todo_list_rearrange_squash(struct todo_list *todo_list)
 		*commit_todo_item_at(&commit_todo, item->commit) = item;
 
 		parse_commit(item->commit);
-		commit_buffer = get_commit_buffer(item->commit, NULL);
+		commit_buffer = logmsg_reencode(item->commit, NULL, "UTF-8");
 		find_commit_subject(commit_buffer, &subject);
 		format_subject(&buf, subject, " ");
 		subject = subjects[i] = strbuf_detach(&buf, &subject_len);

-- 
2.24.0.rc1.3.g89530838a3.dirty