Occasionally our builds have been failing with the error "Unexpected
end of JSON input", with a stack pointing at `lavamoat-core`. The file
in question was reading the policy, reading overrides, merging them,
then writing the policy back to disk.
The intermittent errors can be explained if the policy file was read in
one process while it was being written in another. The extension build
script builds bundles in multiple processes in parallel, so it does
follow that this would happen some of the time. This could result in a
partial policy file being read by the build script, resulting in a JSON
parsing error.
This has been fixed by removing the policy write step using a patch.
We don't need this step. We update the policy using a different
function altogether, and we have a CI job to ensure we never forget to
update it.
Unlike Yarn Classic, Yarn Berry will not verify that the current version
of Node being used matches the `engines` field in `package.json`.
However, someone has written a plugin, [`engines`][1], that provides
this missing functionality, and this commits adds that plugin. This
should ensure that all developers are using the correct version of Node.
(In addition to checking the current Node version, the plugin also
checks the current Yarn version.)
[1]: https://github.com/devoto13/yarn-plugin-engines
