MacPorts 2.11.0: oddly named workdirs

[Chris Jones]

>> All the paths like /opt/local/var/macports/build/rootHGGlRz need to go 
>> back to something predictable and stable for each port build for the 
>> ccache option to be useful again.
> This means that ccache was already effectively unable to cache results 
> for (unchanged) files across version updates, right? 

Yes, but thats much less a problem. The main problem right now is I 
cannot rebuild a large port like LLVM with a trivial fix to the port, 
that doesn't change the version etc. and utilize the hot ccache. The 
random string renders it useless.

It looks like the
> solution according to the ccache docs is to pass relative paths to the 
> compiler. I don't know how to make LLVM's build system do that.

I don't think we can blame upstream projects for this, and fixing *all* 
of them to work with a change we have made on our side does not seem 
reasonable to me.

> 
> There are some environment variables that might work around the issue: 
> <https://ccache.dev/manual/latest.html#_configuration_options>

The problem with those options is they all effectively change the build 
command that is run, replacing paths. Maybe you could get that approach 
to work for *one* upstream project, if that is all we needed to fix, but 
getting something to work again for all port build seems unfeasible.

> 
> The trouble with predictable work dir names is that it's basically 
> impossible for them to be both short and guaranteed to be unique. It 
> might be possible for them to be somewhat "sticky" (likely to stay the 
> same for the same port), though that would require some state to survive 
> a clean, which we don't currently have a way of doing.

I think this is effectively the only fix, find a way to have something 
slightly less random than we have now. Maybe some sort of string hash of 
meta-data related to the port that results in a 'random' string but one 
that doesn't change if the port is rebuilt with no portfile changes, or 
just small ones (that don't e.g. change the port version or things like 
that).

Or, whenever the ccached option is enable just go back to what we where 
doing before and accept the longer path names might cause issues in some 
cases...



> 
> - Josh