Re: [gentoo-dev] [EAPI 6] src_fetch() for fetching live sources

[Ian Stakenvicius]

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On 27/08/13 06:01 AM, Michał Górny wrote:
> Hello, all.
>
> As the next item for discussion in EAPI 6 I'd like to raise the
> idea of introducing src_fetch() phase for fetching live sources.
>
> First of all, I'd like to emphasize that the additional phase
> function will not make live ebuilds any more welcome than they are
> now. They will still be discouraged, and subject to masking as
> usual. However, the function will improve the experience of users
> using them.
>
> The major goal is to add a src_fetch() phase that could be called
> earlier during the ebuild process (e.g. within a parallel fetching
> process) or in a 'emerge --fetchonly' or similar call.
>
> I will sum up the issues that came up already. However, feel free
> to point out any more questions if you have some.
>

0.  Why src_fetch() instead of pkg_fetch() ?  Technically this would
be running based on the package and may not even need to touch ${S} if
the implementation just handles getting the sources to a state where a
src_unpack() can copy them over.  Being a pkg_* would also keep it out
of the standbox (as i believe convention is that all src_* are
supposed to be sandboxed, correct??)



>
> 1. How should we state fetch dependencies?
>
> Most of live ebuilds would need a dependency on the VCS they're
> using. Currently, those dependencies are part of DEPEND. However,
> if src_fetch() is done early or out-of-process, it will no longer
> be good enough for us.
>
> I see two major directions here:
>
> a) explicitly stating fetch dependencies (as FDEPEND or using
> magical USE flag thingie in DEPEND). Then, those dependencies would
> be pulled in earlier than other DEPENDs and installed before
> src_fetch() is called.
>
> I think this will require more work on Zac's side. Also, should we
> then install VCS-es during 'emerge --fetchonly'?
>

This could be handled via support from the PM, too.  IE, if you want
to be able to install git-based live ebuilds either install git by
hand or have USE="git" enabled on portage/paludis/etc.

Either way, it does make sense to have the fetcher (and by extension,
possibly also the unarchiver??) as a separate dependency type instead
of being in DEPEND, since these would technically be packages that the
PM itself needs now to do its thing rather than the software package.


> 2. Should src_unpack() be disallowed from fetching VCS sources?
>
> If we introduce src_fetch() in EAPI 6, then we should probably
> expect all the live eclasses to use that rather than src_unpack()
> for fetching. If we agree on this, we can extend portage's
> network-sandbox to this phase, and likely filesystem sandbox as
> well.
>

The portage network-sandbox feature is going to have to act in an
EAPI-specific way -- ie, there's still plenty of EAPI5 and lower
ebuilds that will inherit say, git-2.eclass and therefore that eclass
will still need to support doing its bits in src_unpack.


> 3. Is everyone ok with splitting VCS fetch into fetch+unpack?
>
> That is, the new design would be like:
>
> - src_fetch() fetches the updates from remote server to DISTDIR,
>
> - src_unpack() does the checkout from DISTDIR to S.
>
> I suspect that some live ebuilds may prefer different kind of
> operation but this split seems quite reasonable.

This implementation makes a lot of sense to me.  In terms of the
specific implementation, I assume both src_fetch and src_unpack be
imeplemented in i.e. git-2.eclass?  Or would there be an accompanying
change to the default src_unpack behaviour to, say, '[[ -z $A ]] && cp
- -r ${VCSDIR} ${S}' for EAPI6 ?



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