Re: [gentoo-dev] RFD: EAPI specification in ebuilds

["Michał Górny" <mgorny@gentoo.org>]

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On Wed, 7 Mar 2012 20:12:25 -0800
Alec Warner <antarus@gentoo.org> wrote:

> On Wed, Mar 7, 2012 at 12:41 PM, Ulrich Mueller <ulm@gentoo.org>
> wrote:
> > Hi all,
> >
> > The way how we currently specify the EAPI in ebuilds has some
> > problems. For example, there is no sane way to allow usage of
> > features of a new bash version in a new EAPI. So we are currently
> > stuck with bash 3.2. Also changes of global scope behaviour, like
> > addition of new global scope functions (similar to "inherit") are
> > not possible.
> >
> > These flaws are outlined in GLEP 55 [1]:
> > | In order to get the EAPI the package manager needs to source the
> > | ebuild, which itself needs the EAPI in the first place. Otherwise
> > it | imposes a serious limitation, namely every ebuild, using any
> > of the | future EAPIs, will have to be source'able by old package
> > managers | [...]
> >
> > The council has voted down GLEP 55 more than a year ago, but at the
> > same time requested that a solution for the mentioned issues should
> > be found. [2] However, there was no progress since then.
> >
> > The issue arose again in bug 402167 [3] where several solutions have
> > been discussed. Below, I try to summarise the possible options
> > resulting from that discussion.
> >
> >
> > *** Proposal 1: "Parse the EAPI assignment statement" ***
> >
> > This first proposal would require that the syntax of the EAPI
> > assignment statement in ebuilds matches a well defined regular
> > expression. A scan of the Portage tree shows that the statement only
> > occurs in the following variations (using EAPI 4 as example):
> >
> >   EAPI=4
> >   EAPI="4"
> >   EAPI='4'
> >
> > Sometimes this is followed by whitespace or a comment (starting with
> > a # sign). Also, with very few exceptions the EAPI assignment occurs
> > within the first few lines of the ebuild. For the vast majority of
> > ebuilds it is in line 5.
> >
> > Written in a more formal way, appropriate for a specification:
> > - Ebuilds must contain at most one EAPI assignment statement.
> > - It must occur within the first N lines of the ebuild (N=10 and
> > N=30 have been suggested).
> > - The statement must match the following regular expression
> > (extended regexp syntax):
> >  ^[ \t]*EAPI=(['"]?)([A-Za-z0-9._+-]*)\1[ \t]*(#.*)?$
> >
> > Note: The first and the third point are already fulfilled by all
> > ebuilds in the Portage tree. The second point will require very few
> > ebuilds to be changed (9 packages for N=10, or 2 packages for N=30).
> >
> > The package manager would determine the EAPI by parsing the
> > assignment with above regular expression. A sanity check would be
> > added. Citing Zac Medico in [3]: "The fact that we can compare the
> > probed EAPI to the actual EAPI variable after the ebuild is sourced
> > seems like a perfect sanity check. We could easily detect
> > inconsistencies and flag such ebuilds as invalid, providing a
> > reliable feedback mechanism to ebuild developers."
> >
> > This proposal comes in two variants:
> > 1a) The change is applied retroactively for all EAPIs.
> > 1b) It is only applied for EAPI 5 and later (which means that the
> >    result of the EAPI parsing would be discarded for earlier EAPIs).
> 
> I don't like this idea because the sane way should be easy and
> straightforward. Mixing a constant declaration with bash assignment
> just confuses users who think the assignment is full bash when in
> fact it is not.
> 
> EAPI=$(somefunc)
> EAPI=${SOMEVAR%%-*}
> and so forth all don't meet the regex (and would be flagged invalid.)
> However a naive author might think they work.

And they all should be invalid due to our policies. The most important
ebuild variables like EAPI should be readable on sight, without having
to lookup random variables, functions etc.

-- 
Best regards,
Michał Górny

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