One more comment:

this isn't based on files/ content, it's based on an existing SYSROOT which simply does not work.  cros-firmware_setup_source is called in global scope which calls setup_source_unibuild which calls get_model_conf_value which directly reads from ROOT.

when you emerge this package, there is no guarantee that ROOT exists or is even set.  portage generates global metadata (like SRC_URI) w/out any board context and caches it so that it can use it later on for speed.  this isn't something you can just punt on "and figure out later".

This package has a depend:

        unibuild? ( chromeos-base/chromeos-config )

so I would expect the config file to be present when this ebuild is used. It does seem to work locally but perhaps it would have problems in a buildbot?

Ideas:

1. Is there a way to turn off the SRC_URI caching on this ebuild?

2. The whole SRC_URI thing does feel a bit brittle. Is there a way to manually download files given a URI?

3. I'd prefer to avoid doing all this processing before the ebuild is properly being run. Can we move it into a normal ebuild function so that it runs as part of src_prepare(), for example?

Proposed approach is here:

https://chromium-review.googlesource.com/c/470407/

> so I would expect the config file to be present when this ebuild is used. It does seem to work locally but perhaps it would have problems in a buildbot?

DEPEND/RDEPEND is irrelevant -- fetching is run independently & in parallel before anything is compiled or installed.  this is an explicit design decision, and a good one imo.

> 1. Is there a way to turn off the SRC_URI caching on this ebuild?

no, nor does such a thing make sense

> 2. The whole SRC_URI thing does feel a bit brittle. Is there a way to manually download files given a URI?

we do not permit ebuilds/eclasses to download files themselves.  it's a bad idea and does not play with caching, reliability, or security.

> 3. I'd prefer to avoid doing all this processing before the ebuild is properly being run. Can we move it into a normal ebuild function so that it runs as part of src_prepare(), for example?

also not feasible or desirable

I've done a change that relies only the source files via a symlink and does not access the root. Hopefully this will resolve this issue.

https://chromium-review.googlesource.com/c/458899/

Seems to work OK, so I'm closing this.