Release v0.0.52 of holonix is up which contains rust nightly-2019-11-15.
Note that the nix mozilla overlay states 2019-11-16 for the date but this is because the overlay is out of sync with the version reported by rustc (version v51 of holonix had a bug where cargo clippy was missing due to this mismatch). Use holonix v52 not v51.
The main reason for the upgrade is to track various things that have stabilised upstream as of rust version 1.39.0.
Notably async/await has landed, including some bug fixes that we need and were missing due to us using an older release candidate.
We are still tracking nightly due to our usage of -Z flags during compilation (e.g. thinlto for incremental compilation support) and some APIs that have not yet stabilised such as TryFrom that allows us to automatically serialize/deserialize data with the potential for failure in the case of bad data.
Our experience is that this nightly upgrade is much less disruptive than past iterations have been but YMMV so plan for some minor refactoring when upgrading to holonix v0.0.52.
Note also that as of the time of writing this version has NOT hit the love branch.
We are still testing our performance improvements and bug fixes from holochain v0.0.40 binaries before we commit to blessing a new holonix release (Holochain release "blessing").