[Commented On] D10770: docket: make compatible with py3.6, where Struct.format is bytes

[durin42 (Augie Fackler)]

durin42 added a comment.


  In D10770#165223 <https://phab.mercurial-scm.org/D10770#165223>, @marmoute wrote:
  
  > In D10770#165221 <https://phab.mercurial-scm.org/D10770#165221>, @durin42 wrote:
  >
  >> In D10770#164629 <https://phab.mercurial-scm.org/D10770#164629>, @marmoute wrote:
  >>
  >>> In D10770#164628 <https://phab.mercurial-scm.org/D10770#164628>, @martinvonz wrote:
  >>>
  >>>> In D10770#164626 <https://phab.mercurial-scm.org/D10770#164626>, @marmoute wrote:
  >>>>
  >>>>> Looks like this is happening because of an inconsistency betwen the fact we passe a binary 'struct' for INDEX_HEADER and a sysstr for the extra once. I would rather fix this by making them consistent.
  >>>>
  >>>> I'm not sure I understand. Can you show me how?
  >>>>
  >>>>   $ python3.6 -c 'import struct; print(type(struct.Struct(b"I").format))'
  >>>>   <class 'bytes'>
  >>>>   $ python3.6 -c 'import struct; print(type(struct.Struct("I").format))'
  >>>>   <class 'bytes'>
  >>>>   $ python3.7 -c 'import struct; print(type(struct.Struct(b"I").format))'
  >>>>   <class 'str'>
  >>>>   $ python3.7 -c 'import struct; print(type(struct.Struct("I").format))'
  >>>>   <class 'str'>
  >>>
  >>> Okay, so my assertion is correct and Python behavior is… creative. Maybe we should build a pycompat wrapper for struct.format access ?
  >>
  >> AFAICT your assertion was wrong: the `struct` module just isn't preserving the input type at all, and always emits `str` on 3.7+, but does `bytes` on 3.6. So we're not mixing bytes/str input types to struct, but instead struct on 3.6 is ninja-converting back to bytes "for" us.
  >
  > Yep, this is a typo on my side (typing is hard) (`is right` because `isn't right`)
  >
  >> A pycompat wrapper would make sense for this if we see more than one case of this. Is that likely?
  >
  > It feels wrong to me to have this kind of compatibility weirdness crawl into normal code. I though more about it and in this case I think the simplest would probably to have the format for `INDEX_HEADER` in a `INDEX_HEADER _FMT` constant and concatenate with that.
  
  Yeah, it feels a bit wrong to me too, but I don't see any great options, esp. w/ the pycompat string tool already doing what we need.
  
  Your solution feels fine-ish, with the caveat that it's more prone to falling out of sync (though I suppose tests would catch that very quickly). I queued this, but if you like the two-constant approach send that as a follow-up?

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  https://phab.mercurial-scm.org/D10770

To: martinvonz, #hg-reviewers, marmoute
Cc: durin42, marmoute, mercurial-patches
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