This means you now get an error message *before* stuff gets built:
$ nix copy .#hydraJobs.vendoredCrates
error: you must pass '--from' and/or '--to'
Try 'nix --help' for more information.
Most functions now take a StorePath argument rather than a Path (which
is just an alias for std::string). The StorePath constructor ensures
that the path is syntactically correct (i.e. it looks like
<store-dir>/<base32-hash>-<name>). Similarly, functions like
buildPaths() now take a StorePathWithOutputs, rather than abusing Path
by adding a '!<outputs>' suffix.
Note that the StorePath type is implemented in Rust. This involves
some hackery to allow Rust values to be used directly in C++, via a
helper type whose destructor calls the Rust type's drop()
function. The main issue is the dynamic nature of C++ move semantics:
after we have moved a Rust value, we should not call the drop function
on the original value. So when we move a value, we set the original
value to bitwise zero, and the destructor only calls drop() if the
value is not bitwise zero. This should be sufficient for most types.
Also lots of minor cleanups to the C++ API to make it more modern
(e.g. using std::optional and std::string_view in some places).
This replaces nix-push. For example,
$ nix copy --to file:///tmp/cache -r $(type -p firefox)
copies the closure of firefox to the specified binary cache. And
$ nix copy --from file:///tmp/cache --to s3://my-cache /nix/store/abcd...
copies between two binary caches.
It will also replace nix-copy-closure, once we have an SSHStore class,
e.g.
$ nix copy --from ssh://alice@machine /nix/store/abcd...
