store reference detection (was Re: JARs and reference scanning)

[Thomas Danckaert <post@thomasdanckaert.be>]

From: Chris Marusich <cmmarusich@gmail.com>
Subject: Re: JARs and reference scanning
Date: Tue, 25 Apr 2017 22:34:02 -0700

>> I have to admit that I do not know at all how the reference 
>> scanning and
>> dependency-tracking in the store works.
>
> As I understand it, the mechanism used by the Guix daemon (and the 
> Nix
> daemon) for scanning references doesn't work when the output of a
> derivation is scrambled in some way (e.g. compressed).  Therefore, 
> if we
> use JAR files, they should not be compressed.

The code scanning for reference is in nix/libstore/references.cc .  
It looks for base32 hashes encoded as character strings in the 
binaries.

Could/should this be generalized somehow?  Apart from compression, 
store filenames encoded with 16-bit character encodings also cause 
problems (can happen with Qt or WxWidgets).  And the are probably 
more cases where it fails.

Does it make sense to expand the reference detecting code (perhaps 
this would lead to too many different special cases?), or maybe 
provide a mechanism to force references when the daemon cannot detect 
them.  I suppose you can always add a text file with a list of store 
items to the output, but maybe there's a more elegant way?

Thomas