Re: [gentoo-portage-dev] [PATCH] ebuild: set up bash compat levels

[Michał Górny]

On Wed, 11 Nov 2015 12:52:05 +0100
Ulrich Mueller <ulm@g.o> wrote:

> >>>>> On Wed, 11 Nov 2015, Michał Górny wrote:
>
> > I'm not convinced we ought to do this for EAPI < 6. It is a breaking
> > change after all, and as such changes the behavior of EAPI < 6
> > ebuilds.
>
> Which according to PMS should assume bash version 3.2. Also, AFAICS
> the only feature where the compat settings could have any impact is
> this setting from compat42:
>
>    If set, bash does not process the replacement string in the pattern
>    substitution word expansion using quote removal.
>
> All other compat changes affect either only POSIX mode, or interactive
> mode, or string comparison (where the compat32 setting disables locale
> specific behaviour and uses strcmp instead, so effectively the compat
> setting should be saner).

Ok, I recalled the issue I was particularly concerned about.

  PV="1_beta2"
  MY_PV="${PV/_/~}"

This triggers different behavior between bash<=4.2 and bash>=4.3, with
the latter requiring:

  PV="1_beta2"
  MY_PV="${PV/_/\~}"

(which in turns breaks older). Now, if someone put a conditional on
BASH_VERSINFO that worked around this discrepancy, introducing
BASH_COMPAT suddenly breaks it by forcing the old behavior when
BASH_VERSINFO indicates the new behavior is expected.

Not saying this is very likely to happen. However, we are clearly
violating the idea behind PMS by allowing it to happen retroactively.

However, enabling BASH_COMPAT in EAPI 6 is a good thing. For example,
because people in EAPI 6 no longer need to be concerned about this
discrepancy.

-- 
Best regards,
Michał Górny
<http://dev.gentoo.org/~mgorny/>