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

[Arnout Vandecappelle <arnout@mind.be>]

On 10/02/2023 22:55, Yann E. MORIN 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(-)
> 
> diff --git a/package/erlang/erlang.mk b/package/erlang/erlang.mk
> index ac2c204a49..5d6b69057a 100644
> --- a/package/erlang/erlang.mk
> +++ b/package/erlang/erlang.mk
> @@ -4,8 +4,8 @@
>   #
>   ################################################################################
>   
> -# See note below when updating Erlang
>   ERLANG_VERSION = 22.3.4.22
> +ERLANG_RELEASE = $(firstword $(subst ., ,$(ERLANG_VERSION)))
>   ERLANG_SITE = \
>   	https://github.com/erlang/otp/releases/download/OTP-$(ERLANG_VERSION)
>   ERLANG_SOURCE = otp_src_$(ERLANG_VERSION).tar.gz
> @@ -36,9 +36,9 @@ ERLANG_PRE_CONFIGURE_HOOKS += ERLANG_RUN_AUTOCONF
>   HOST_ERLANG_DEPENDENCIES += host-autoconf
>   HOST_ERLANG_PRE_CONFIGURE_HOOKS += ERLANG_RUN_AUTOCONF
>   
> -# Whenever updating Erlang, this value should be updated as well, to the
> -# value of EI_VSN in the file lib/erl_interface/vsn.mk
> -ERLANG_EI_VSN = 3.13.2.2
> +# Return the EIV (Erlang Interface Version, EI_VSN)
> +# $(1): base directory, i.e. either $(HOST_DIR) or $(STAGING_DIR)/usr
> +erlang_ei_vsn = `sed -r -e '/^erl_interface-(.+)/!d; s//\1/' $(1)/lib/erlang/releases/$(ERLANG_RELEASE)/installed_application_versions`

  Since this is only used by rebar-package, I think it should move to pkg-rebar.mk.

>   
>   # The configure checks for these functions fail incorrectly
>   ERLANG_CONF_ENV = ac_cv_func_isnan=yes ac_cv_func_isinf=yes
> diff --git a/package/pkg-rebar.mk b/package/pkg-rebar.mk
> index e4e3f3bb6c..4b993dd970 100644
> --- a/package/pkg-rebar.mk
> +++ b/package/pkg-rebar.mk
> @@ -32,10 +32,10 @@ REBAR_TARGET_DEPS_DIR = $(STAGING_DIR)/usr/share/rebar/deps
>   #
>   REBAR_HOST_DEPS_ENV = \
>   	ERL_COMPILER_OPTIONS='{i, "$(REBAR_HOST_DEPS_DIR)"}' \
> -	ERL_EI_LIBDIR=$(HOST_DIR)/lib/erlang/lib/erl_interface-$(ERLANG_EI_VSN)/lib
> +	ERL_EI_LIBDIR=$(HOST_DIR)/lib/erlang/lib/erl_interface-$(call erlang_ei_vsn,$(HOST_DIR))/lib

  Since we support only one erlang version, we could just as well put

$(wildcard $(HOST_DIR)/lib/erlang/lib/erl_interface-*/lib)

or does that directory not necessarily exist yet after erlang has been installed?

  Regards,
  Arnout


>   REBAR_TARGET_DEPS_ENV = \
>   	ERL_COMPILER_OPTIONS='{i, "$(REBAR_TARGET_DEPS_DIR)"}' \
> -	ERL_EI_LIBDIR=$(STAGING_DIR)/usr/lib/erlang/lib/erl_interface-$(ERLANG_EI_VSN)/lib
> +	ERL_EI_LIBDIR=$(STAGING_DIR)/usr/lib/erlang/lib/erl_interface-$(call erlang_ei_vsn,$(STAGING_DIR)/usr)/lib
>   
>   ################################################################################
>   # Helper functions
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