Re: [Buildroot] [PATCH] package/erlang: do not hard-code the Erlang Interface Version (EI_VSN)

From: Thomas Petazzoni via buildroot <buildroot@buildroot.org>
To: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Will Newton <will.newton@gmail.com>,
	Johan Oudinet <johan.oudinet@gmail.com>,
	buildroot@buildroot.org
Subject: Re: [Buildroot] [PATCH] package/erlang: do not hard-code the Erlang Interface Version (EI_VSN)
Date: Thu, 10 Aug 2023 23:16:38 +0200	[thread overview]
Message-ID: <20230810231638.6837c8da@windsurf> (raw)
In-Reply-To: <20230210215548.1050371-1-yann.morin.1998@free.fr>

On Fri, 10 Feb 2023 22:55:48 +0100
"Yann E. MORIN" <yann.morin.1998@free.fr> wrote:

> The note above the erlang version instructs to refer to another note
> further down the file. However, even if it is not too difficult to find,
> it is still located a bit too far away, and the reference is not very
> explicit what note we should look at.
> 
> When we introduced that variable in 6c1d128844c5 (package/erlang: export
> EI_VSN so other packages can use it), the rationale for hard-coding it
> was "to avoid spawning a shell every time the variable is dereferenced".
> 
> However, that can get a bit confusing and hard to follow. Also, that in
> fact spawns a shell only once for each rebar-packages, so the overhead
> is far from being too high.
> 
> The EI_VSN is only used by rebar-package packages, is derefrenced from
> the rebar-infra and not the packages themselves, and is not needed by
> erlang itself (it knows its own EI_VSN), so we can de-hard-code it, and
> rely on build-time detection, by looking in the appropriate file.
> 
> We have two files where we could look:
>   - lib/erl_interface/vsn.mk in the erlang source tree, but it is not
>     installed,
>   - .../lib/erlang/releases/$(ERLANG_RELASE)/installed_application_versions
>     as installed by erlang.
> 
> We use the second one, as it is cleaner, for a package, to look into
> installed files, rather than to look in the source tree of another
> package.
> 
> Although both the host and target erlang are the same, we still look
> into the corresponding file to extract the version. This is so that it
> would be easier if in the future we ever manage to rely on a
> system-installed erlang that could have a EI_VSN different from the
> target one.
> 
> We can't re-use the variable ERLANG_EI_VSN, because it now needs to be
> $(call)-ed with a parameter. Hopefully, external packages that use it
> directly rather than through the rebar infra, are not legion...
> 
> Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
> Cc: Will Newton <will.newton@gmail.com>
> Cc: Johan Oudinet <johan.oudinet@gmail.com>
> ---
>  package/erlang/erlang.mk | 8 ++++----
>  package/pkg-rebar.mk     | 4 ++--
>  2 files changed, 6 insertions(+), 6 deletions(-)

Arnout provided feedback, you replied to it, Arnout never provided
counter feedback, so: I've applied to next. Thanks!

Thomas
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com
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