Configuration is editor-independent. For this reason, we pick
JSON-schema as the repr of the source of truth. We do specify it using
rust-macros and some quick&dirty hackery though.
The idea for syncing truth with package.json is to just do that
manually, but there's a test to check that they are actually synced.
There's CLI to print config's json schema:
$ rust-analyzer --print-config-schema
We go with a CLI rather than LSP request/response to make it easier to
incorporate the thing into extension's static config. This is roughtly
how we put the thing in package.json.
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