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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 6c1d128844 (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>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
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