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To: gentoo-dev@g.o
From: Alec Warner <antarus@g.o>
Subject: Re: RFD: EAPI specification in ebuilds
Date: Wed, 7 Mar 2012 20:12:25 -0800
On Wed, Mar 7, 2012 at 12:41 PM, Ulrich Mueller <ulm@g.o> 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.

and so forth all don't meet the regex (and would be flagged invalid.)
However a naive author might think they work.

I don't think any naive author would think either would work in a comment

# EAPI=$(somefunc)

Bash doesn't parse comments, so confusion is unlikely.

> *** Proposal 2: "EAPI in header comment" ***
> A different approach would be to specify the EAPI in a specially
> formatted comment in the ebuild's header. No syntax has been suggested
> yet, but I believe that the following would work as a specification:
> - The EAPI must be declared in a special comment in the first line of
>  the ebuild's header, as follows:
> - The first line of the ebuild must contain the word "ebuild",
>  followed by whitespace, followed by the EAPI, followed by
>  end-of-line or whitespace.
> Again, the proposal comes in two variants:
> 2a) It is combined with a one time change of the file extension, like
>    .ebuild -> .eb.
> 2b) The usual EAPI assignment statement in the ebuild is still
>    required, at least for a transition period.
> In the 2a case, the EAPI variable could be made read-only in bash
> before sourcing the ebuild. In the 2b case, a sanity check similar to
> the one mentioned above would be added.
> What do you think?

Overloading is bad.

There is no real difference between:
#!/usr/bin/ebuild --eapi 5
# EAPI=5

The problem is that the former is also the way to specify how to
execute the ebuild; so unless you plan to make ebuilds executable and
having /usr/bin/ebuild provide the ebuild environment, using that
syntax is confusing to users.

> (I really hope for a constructive discussion here. So, if you want
> to comment that all of the above proposals suck and GLEP 55 is much
> superior, then please open a new thread for it.)

You don't mention voting on glep 55 again; is there a reason why not?

> Ulrich
> [1] <>
> [2] <>
> [3] <>

Re: RFD: EAPI specification in ebuilds
-- Michał Górny
Re: RFD: EAPI specification in ebuilds
-- Ulrich Mueller
RFD: EAPI specification in ebuilds
-- Ulrich Mueller
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