Re: "Problems" with git format-patch --thread email header ordering

[Linus Torvalds <torvalds@linux-foundation.org>]

On Thu, Mar 14, 2019 at 9:47 PM Junio C Hamano <gitster@pobox.com> wrote:
>
> Linus Torvalds <torvalds@linux-foundation.org> writes:
>
> > While it's true that header ordering isn't specified, there's a common
> > "canonical" order that the headers are listed in. To quote rfc822:
> > ...
> >             body must occur AFTER  the  headers.   It  is  recommended
> >             that,  if  present,  headers be sent in the order "Return-
> >             Path", "Received", "Date",  "From",  "Subject",  "Sender",
> >             "To", "cc", etc.
>
> I obviously won't do the last one myself, but if the issue is only
> to swap from and date, then this may be sufficient, perhaps?

I'm not actually sure _what_ the order requirements for gmail are,
since gmail itself doesn't seem to honor them. Does the order of the
Message-ID header line matter, for example?

I don't think it's the order of the From/Date lines, actually, because
google itself doesn't do that.

What Thomas Found out was that the exact same email with

    Message-Id/From/Date/Subject/To

(in that order) does not work, but

    Date/From/Subject/To/Message-Id

does work. Weird and "wonderful". But there might be a lot of other
orderings that work or don't.

Having looked through some other emails, I know that

    From/To/Subject/Date/Message-Id
    Subject/To/References/From/Message-ID/Date

also works.  Which makes me suspect that it's the Message-ID line that matters.

But it might be something _really_ odd, and maybe not just ordering at
all (ie it might be something where gmail wants to see the "From"
line, but only in certain circumstances, and only *then* does it
matter if the From line comes before some other line or not.

All we know is

 (a) gmail complains about the normal git format-patch ordering with a
"no From line" bounce

 (b) the same email with just headers re-ordered goes through

I *suspect* it's that Message-ID line, but .... It's very annoying.

               Linus