# [PATCH] pretty: add X-Change-ID to mail formats 3 messages from 2025-07-03 to 2025-07-03. Participants: Drew DeVault, Remo Senekowitsch. Thread: https://gitlist.dev/t/63733 ## Drew DeVault, 2025-07-03 07:45 Subject: [PATCH] pretty: add X-Change-ID to mail formats Message-ID: <20250703074952.20737-1-drew@ddevault.org> URL: https://gitlist.dev/e/20250703074952.20737-1-drew%40ddevault.org ``` Introduce the X-Change-ID header to emails prepared by git (i.e. via format-patch, send-email). This allows tools which work with those emails (e.g. patchwork, sourcehut) to meaningfully integrate with tools that assign change IDs to commits. With some follow-up work, this is also the first step towards ensuring that those change IDs are preserved through from git-send-email to git-am as a change moves through its review lifecycle. Signed-off-by: Drew DeVault --- I have refrained from implementing the git-am part of this work for now, on the basis that I'm not sure how downstream tools like Jujutsu would feel if git wrote the change-id header to new commits. Would that conflict with some internal deterministic process for coming up with the change-id that could come up with a different answer, leading to conflicts? I don't know, so I would appreciate some insights from those who understand the implications for their downstream systems. Adding the change ID to outgoing emails is useful on its own, however, so I think this patch is acceptable without the git-am side being initially present. pretty.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/pretty.c b/pretty.c index 0bc8ad8a9a..70fba7b023 100644 --- a/pretty.c +++ b/pretty.c @@ -2045,7 +2045,7 @@ static void pp_header(struct pretty_print_context *pp, int parents_shown = 0; for (;;) { - const char *name, *line = *msg_p; + const char *name, *change_id, *line = *msg_p; int linelen = get_one_line(*msg_p); if (!linelen) @@ -2089,6 +2089,11 @@ static void pp_header(struct pretty_print_context *pp, strbuf_grow(sb, linelen + 80); pp_user_info(pp, "Commit", sb, name, encoding); } + if (skip_prefix(line, "change-id ", &change_id) && + cmit_fmt_is_mail(pp->fmt)) { + strbuf_addf(sb, "X-Change-ID: %.*s\n", + linelen - 11, change_id); + } } } -- 2.50.0 ``` ## Remo Senekowitsch, 2025-07-03 08:41 Subject: Re: [PATCH] pretty: add X-Change-ID to mail formats Message-ID: URL: https://gitlist.dev/e/DB2AARC4OKR3.48T4CC70KBUC%40buenzli.dev In-Reply-To: <20250703074952.20737-1-drew@ddevault.org> ``` Hi Drew, Thank you, this is exciting! On Thu Jul 3, 2025 at 9:45 AM CEST, Drew DeVault wrote: > I have refrained from implementing the git-am part of this work for now, > on the basis that I'm not sure how downstream tools like Jujutsu would > feel if git wrote the change-id header to new commits. Would that > conflict with some internal deterministic process for coming up with the > change-id that could come up with a different answer, leading to > conflicts? This would be no problem at all. Jujutsu would very much welcome if Git preserved the change-id header, including for patches sent by email. Jujutsu generates the initial change-id randomly and since any part of the commit can change while the change-id remains stable, there is no deterministic process that could be interfered with if Git wrote the change-id header to new commits. So, there are no objections from my side to implementing the git-am part as well. :-) This can kind of be tested already. Because Jujutsu already writes the change-id header and sends it via git push, it must also be able to import those headers from commits it hasn't seen before. Possible steps to verify this behavior: * Create a repo with Jujutsu, make some commits, push them to a remote. (can be one on the local file system) * Clone this repo via Git. * (optional) Confirm with `git cat-file -p @` that the change-id header was preserved. * Run `jj git init --colocate .` to upgrade the git repo to a jj repo. * Run `jj log` and observe that Jujutsu correctly imported the change-id headers of existing commits it didn't know about previously. Best regards, Remo ``` ## Drew DeVault, 2025-07-03 11:32 Subject: Re: [PATCH] pretty: add X-Change-ID to mail formats Message-ID: URL: https://gitlist.dev/e/DB2DY0C84G1R.3V7LEG87PHVTW%40ddevault.org In-Reply-To: ``` Sweet! I'm going to send a follow-up with git-am support. On Thu Jul 3, 2025 at 10:41 AM CEST, Remo Senekowitsch wrote: > This can kind of be tested already. Because Jujutsu already writes the > change-id header and sends it via git push, it must also be able to > import those headers from commits it hasn't seen before. Possible steps > to verify this behavior: > > * Create a repo with Jujutsu, make some commits, push them to a remote. > (can be one on the local file system) > > * Clone this repo via Git. > > * (optional) Confirm with `git cat-file -p @` that the change-id header > was preserved. > > * Run `jj git init --colocate .` to upgrade the git repo to a jj repo. > > * Run `jj log` and observe that Jujutsu correctly imported the change-id > headers of existing commits it didn't know about previously. I can confirm all of this works with the v2 I'm about to send, though I have ascertained as much through a manual testing procedure that resembles your recommendation here. One thing I'm less certain about is how to expand the tests in t/ to test this behavior. I'll elaborate in the timely commentary of v2. ```