[vlc-devel] [PATCH v2 5/6] contrib: lua: autodetect lua >= 5.1

[Alexandre Janniaux]

Hi,

On Mon, Nov 16, 2020 at 07:56:06AM +0100, Steve Lhomme wrote:
> On 2020-11-14 16:30, Alexandre Janniaux wrote:
> > When building on ArchLinux currently, the contrib was built even if
> > lua5.3 is installed. As at least Archlinux and Debian are exposing both
> > a luaX.Y.pc and lua.pc file for the latest supported version of lua,
> > detecting that the system version is correct through lua.pc should
> > also ensure that the latest compatible version is installed and used
> > instead.
> >
> > The other checks are still needed as you can for example install lua5.2
> > (which will expose a lua5.2.pc file but no lua.pc file) without having
> > to install lua (5.3).
> >
> > It is worth noticing that being able to use lua >= 5.1 doesn't mean any
> > version of lua >= 5.1 would be compatible. The source code is completely
> > compliant to those version and native builds will have no issues with
> > using a more recent version, but cross-compilation environment for 32bit
> > environment from a 64bit one won't and need the appropriate version to
> > be installed.
>
> I think that's the whole point. We only want to compile with Lua 5.2. If Lua
> 8.12 is available on the system we are not going to use it properly.

We don't do that for other libraries. The point is to run with the one
you link against. If maintainers link against an invalid lua version
then it would fail just like if you update a library that is not
compatible with VLC.

The error could be at runtime for lua though, instead of loading time,
because a script would fail, which could movtivate a pinned version on
the maintainer, but this is irrelevant in the contrib rules: order
doesn't matter here.

However, it's correctly handled within the configure script: if you
compile with lua5.2 available, it will always use the lua5.2 version,
and same with lua5.1. If you compile against liblua, it will use liblua
regardless of the version >= 5.1 like other libraries we use.

Note that typically the header/library probe is not checking the
version already, so currently not only it would use my lua library on
the system, but in addition it would compile the contrib and use the
headers in contrib, leading to linkage errors.

Regards,
--
Alexandre Janniaux
Videolabs


> > ---
> >   contrib/src/lua/rules.mak | 3 +++
> >   1 file changed, 3 insertions(+)
> >
> > diff --git a/contrib/src/lua/rules.mak b/contrib/src/lua/rules.mak
> > index 491353b484..c64eb6299d 100644
> > --- a/contrib/src/lua/rules.mak
> > +++ b/contrib/src/lua/rules.mak
> > @@ -28,6 +28,9 @@ endif
> >   # Feel free to add autodetection if you need to...
> >   PKGS += lua luac
> >   PKGS_ALL += luac
> > +ifeq ($(call need_pkg,"lua >= 5.1"),)
> > +PKGS_FOUND += lua luac
> > +endif
> >   ifeq ($(call need_pkg,"lua5.2"),)
> >   PKGS_FOUND += lua luac
> >   endif
> > --
> > 2.29.2
> >
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