[Nix-dev] break purity

[stewart mackenzie]

Hi,

I've got a bunch of artifacts being built in the
/tmp/nix-build-component_name.drv-0

now I want to point the build manager, in this case cargo using the
CARGO_TARGET_DIR env var to put the artifacts into a directory I make
directly in the /tmp/target_${name}

This way any further compilations will reuse the artifacts and they
won't need to be rebuilt.

obviously nix doesn't allow me to do this.

Is there a dirty hack to allow creating and writing artifacts directly
to /tmp/target_${name}?

Why? We're using nix as a replacement for make, one major drawback is:
every time we change a line of code the entire component + trans deps
needs to be rebuilt. This takes a long time when transitive deps go
deep.

/sjm