[Nix-dev] Manual Downloads of Proprietary Software

[Shea Levy]

Hi all,

Some software (e.g. Adobe Air) requires that the person installing it 
agree to certain terms prior to downloading the file. While in many 
(though not all) cases it is possible to simply put the download URL 
into a nix expression and have nix download the file automatically, such 
circumvention of the terms-and-conditions agreement seems legally shaky 
at best. As such, I would like to create a function that looks for a 
file on the local filesystem and aborts with a message that the user 
must download the file manually before building the derivation (if such 
a function already exists, please let me know). My question for the list 
is this: How should the function find the file? I can think of three 
ways, but I'm not sure which is best: having the user download the file 
to a hard-coded location, having the user set an env var with the 
location of the file, or having the user nix-store --add the file 
manually. Or is there a better solution than any of these?

Cheers,
Shea Levy