#25425 lua does not set search paths

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From: Ricardo Wurmus <rekado@elephly.net>
To: Ludovic Courtès <ludo@gnu.org>
Subject: Re: bug#25425: cannot express search path
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Date: Sun, 22 Jan 2017 23:34:00 +0100
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Ludovic Courtès <ludo@gnu.org> writes:

> Hello!
>
> Ricardo Wurmus <rekado@elephly.net> skribis:
>
>> Ludovic Courtès <ludo@gnu.org> writes:
>>
>>> I think this should work:
>>>
>>>        (search-path-specification
>>>          (variable "LUA_PATH")
>>>          (separator ";")
>>>          (files '("share/lua/5.3"))
>>>          (file-pattern "\\.lua$")
>>>          (file-type 'regular))
>>
>> I tried this very same thing but it doesn’t work because Lua expects
>> placeholders (“?”) in the search paths.  The placeholders are replaced
>> with the actual package names.  If the actual file name does not exist
>> it will try the next pattern.  If the file *does* exist – which *will* be
>> the case for any of the files on LUA_PATH that have been generated by
>> the search-path-specification — Lua will try to load the package from
>> that path.
>>
>> This will fail because a search for the “lpeg” module would be satisfied
>> by the file “re.lua”, because that’s the first valid file on the
>> LUA_PATH.  “re.lua” requires “lpeg” itself, so another lookup is
>> performed, which will again result in “re.lua” to be loaded…
>>
>> AIUI we must generate a value for LUA_PATH that keeps the placeholders
>> intact.
>
> So are you saying that it’s important for the question marks to remain
> intact?

Yes, that seems to be the case.

> This sounds terrible.  I’m not sure how to address it, and I don’t feel
> like stretching the search path mechanism this much.
>
> Thoughts?

I agree.  It’s a really odd special case.  On the other hand, not
extending the search path mechanism would mean that we have to find
other ways to fix “guix environment”, build phases, and profiles when
Lua packages are involved.

Build phases are easy to fix (by using a procedure that sets the
appropriate environment variables depending on the build inputs), but I
don’t know how to make profiles behave the way they should.  Maybe it
would be fine to set a single value for LUA_PATH (and LUA_CPATH) that
assumes a single prefix (the profile path) and contains the necessary
placeholders.

--
Ricardo

GPG: BCA6 89B6 3655 3801 C3C6  2150 197A 5888 235F ACAC
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