Re: [PATCH v2] range-diff: support reading mbox files

> [...]
>> I'm a bit confused by this sed command, I've annotated it with my probably
>> flawed understanding.
>>
>>>        ++	sed -e "/^From: .*/{
>>>        ++		h
>>
>> This stores the From: header in the hold space
> 
> 👍
> 
>>>        ++		s/.*/From: Bugs Bunny <bugs@bun.ny>/
>>
>> This changes the From: header in the pattern space
> 
> 👍
> 
>>>        ++		:1
>>>        ++		N
>>>        ++		/[ -z]$/b1
>>
>> We loop until we find a line that does not end with a space, letter or number
>> adding the lines to the hold space
> 
> I would have _loved_ to match on an empty line, i.e. `/[^\n]$/b1`. But
> that construct is not understood by the `sed` on macOS.

> I even went so far as to search for the source code of a BSD `sed` (and I
> found it, and modified the code so that it builds on Linux, see
> https://github.com/dscho/sed-bsd) to try a couple of things, but could not
> make it work with any variation of `\n`. Therefore, I settled on expecting
> all the lines in the commit header to end in printable ASCII characters
> between the space and the `z`.
> 
>>>        ++		G
>>
>> This appends the hold space to the pattern space, then the pattern space is
>> printed.
> 
> 👍
> 
>> Doesn't this mean we end up with two From: headers? Is the in-body From:
>> line already present?
> 
> There is no in-body `From:` header because the patch author matches the
> `GIT_AUTHOR_IDENT` that is in effect while running the `format-patch`
> command.
> 
> Let me show you what this `sed` call deals with. In the local test run, it
> modified an `mbox` starting with this:

> 	From 4d39cb329d3ef4c8e69b43859c2e11adb83f8613 Mon Sep 17 00:00:00 2001
> 	From: Thomas Rast <trast@inf.ethz.ch>
> 	Date: Mon, 22 Jul 2013 11:23:44 +0200
> 	Subject: [PATCH 1/3] s/4/A/ + add other-file
> 
> 	---
> 	  file       | 2 +-
> 	  other-file | 0
> 	  [...]
> 
> to a modified `mbox` that starts with this:
> 
> 	From 4d39cb329d3ef4c8e69b43859c2e11adb83f8613 Mon Sep 17 00:00:00 2001
> 	From: Bugs Bunny <bugs@bun.ny>
> 	Date: Mon, 22 Jul 2013 11:23:44 +0200
> 	Subject: [PATCH 1/3] s/4/A/ + add other-file
> 
> 	From: Thomas Rast <trast@inf.ethz.ch>
> 	---
> 	  file       | 2 +-
> 	  other-file | 0
> 	  [...]
> 
>>
>>>        ++	}" <mbox >mbox.from &&
>>>        ++	git range-diff mode-only-change..topic mbox:./mbox.from
>>>        >actual.from &&
>>>        ++	test_cmp expect actual.from &&
>>>        ++
>>>        ++	append_cr <mbox >mbox.cr &&
>>>        ++	test_must_fail git range-diff \
>>>        ++		mode-only-change..topic mbox:./mbox.cr 2>err &&
>>>        ++	grep CR/LF err &&
>>
>> Thanks for adding that
> 
> Thank you for the suggestion to add it!
> 
> And thank you again for modeling how to perform actionable, helpful and
> productive code reviews,