Setting the GOROOT_FINAL environment variables replaces the absolute
location of the Go standard library sources in the final build
artefacts with a fake location (in this case starting with
go/src/...).
This is despite the documentation for 'trimpath' (in 'go tool
compile') stating that it would affect all source paths: That's only
true for user code!
I figured this out by reading through the implementation of the other
'trimpath' (in 'gob build'):
https://go-review.googlesource.com/c/go/+/173345
This moves the various projects from "type-based" folders (such as
"services" or "tools") into more appropriate semantic folders (such as
"nix", "ops" or "web").
Deprecated projects (nixcon-demo & gotest) which only existed for
testing/demonstration purposes have been removed.
(Note: *all* builds are broken with this commit)
