[Buildroot] Making the Luarocks integration compatible with per-package folders

[Thomas Petazzoni <thomas.petazzoni@bootlin.com>]

Fran?ois,

I don't know if you have followed the discussion, but I recently sent a
new iteration of the per-package folder series [1], which allows to
support top-level parallel build.

Currently the Luarocks integration in Buildroot doesn't work with this
per-package folder stuff.

I fixed a first problem in http://patchwork.ozlabs.org/patch/998962/,
which prevented the host luarocks binary from being available to
Luarocks packages.

But then the build still doesn't work, with the following error:

>>> dado 1.8.3-1 Building
>>> dado 1.8.3-1 Installing to target
cd /home/thomas/projets/buildroot/output/build/dado-1.8.3-1/dado-1.8.3 && LUA_PATH="/home/thomas/projets/buildroot/output/per-package/dado/host/share/lua/5.3/?.lua" flock /home/thomas/projets/buildroot/output/per-package/dado/target /home/thomas/projets/buildroot/output/per-package/dado/host/bin/lua /home/thomas/projets/buildroot/output/per-package/dado/host/bin/luarocks make --keep dado-1.8.3-1.rockspec 

Error: Failed finding Lua library. You may need to configure LUA_LIBDIR.
make[1]: *** [package/pkg-generic.mk:337: /home/thomas/projets/buildroot/output/build/dado-1.8.3-1/.stamp_target_installed] Error 1
make: *** [Makefile:84: _all] Error 2

(You can reproduce this issue by using
https://git.bootlin.com/users/thomas-petazzoni/buildroot/log/?h=ppsh-v4
+ http://patchwork.ozlabs.org/patch/998962/, and simply building any
Luarocks package).

I have not investigated in details, but I believe that the problem
comes from the /etc/luarocks/config-5.3.lua file in $(HOST_DIR), which
contains a number of absolute paths to the $(HOST_DIR) and
$(STAGING_DIR), but at the time of the host-luarocks build. This works
fine when per-package folder is disabled because there is a single
HOST_DIR and a single STAGING_DIR, global to all packages. But the
whole purpose of per-package folders is to have separate HOST_DIR (and
therefore STAGING_DIR) for each package.

So, we would need to change this config-5.3.lua file, and we have two
options:

 (1) Either we can use relative paths in this file, or make it use
     environment variables. In this case, we can keep a single instance
     of this file, and ensure it behaves properly for each package thanks
     to the relative path and/or environment variables passed during the
     build.

 (2) Or if the first option doesn't work, we have to create a separate
     version of config-5.3.lua for each package that we build.

Do you know if option (1) is doable ? If not, are you
interested/available to work on option (2) ? If not, I'm willing to try
to implement it, but I might need some help since I'm not familiar with
luarocks.

Thanks for your help!

Thomas

[1] http://patchwork.ozlabs.org/project/buildroot/list/?series=75909
-- 
Thomas Petazzoni, CTO, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com