Subject: Re: bug#50072: [PATCH WIP 0/4] Add upstream updater for git-fetch origins.

From: zimoun <[email-masked]>
Date: Wed, 05 Jan 2022 12:48:48 +0100

Hi Maxime,

On Wed, 05 Jan 2022 at 11:07, Maxime Devos <[email-masked]> wrote:

> Precisely, in the sense 'auto' means #true in that 'auto' recurses.
> But sometimes #true / auto compute a different hash ...

[...]

> No, when #:recursive? is 'auto' and the file is a directory, it
> recurses. When it is 'auto' and the file is a regular file, then
> it also recurses, albeit in a trivial way (because regular files don't
> contain other files).
>
> This comment explains that the 'recursive hash' (nar hash) and 'regular
> hash' of a regular file are different, that usually you want the
> regular hash for regular files, and implies that '#:recursive? auto'
> usually does the right thing.
>
> But if you really want the recursive hash for regular files, then you
> can still compute that by setting #:recursive? #true.

Thanks for explaining.

Hm, my confusion is probably the same as #51307 [1].

1: <https://issues.guix.gnu.org/51307#12>

Well, I think ’#:recursive?’ is confusing, and ’auto’ too because it is
not POLA for a plumbing function, IMHO.  Anyway. It is v4 and it is
ready to merge. :-)

I just propose to replace ’#:recursive?’ by ’#:nar-serializer?’ and a
docstring along these lines,

--8<---------------cut here---------------start------------->8---
  "Compute the hash of FILE with ALGORITHM.  If NAR-SERIALIZER? is
  #true, compute the combined hash (NAR hash) of FILE for which (SELECT?
  FILE STAT) returns true.

  If NAR-SERIALIZER? is #false, compute the regular hash using the
  default serializer.  It is meant to be used for a regular file.

  If NAR-SERIALIZER? is 'auto', when FILE is a directory, compute the
  combined hash (NAR hash).  When FILE is a regular file, compute the
  regular hash using the default serializer.  The option ’auto’ is meant
  to apply by default the expected hash computation.

  Symbolic links are not dereferenced unless NAR-SERIALIZER? is false.

  This procedure must only be used under controlled circumstances; the
  detection of symbolic links in FILE is racy.
--8<---------------cut here---------------end--------------->8---

WDYT?

>> > +  (if (or (eq? recursive? #true)
>> > +          (and (eq? recursive? 'auto)
>> 
>> …the symbol ’auto’ is only used here.  IIRC all the series. :-)
>
> In ‘[PATCH v4 3/4] refresh: Support non-tarball sources.’, there's
>
>> +                (let ((hash (file-hash* output)))
>
> There, #:recursive? is 'auto'.

Naive questions: Is it mandatory?  Or can be explicitly set?

(I have nothing against, just to me ’auto’ is somehow ambiguous and «In
the face of ambiguity, refuse the temptation to guess» as ’pyhon3 -c
'import this'’ says ;-))

Cheers,
simon