Documentation

For general server architecture, see README.md. This module implements the watchdog process.

Watchdog state #

Most LSP clients only send us file diffs, so to facilitate sending entire file contents to freshly restarted workers, the watchdog needs to maintain the current state of each file. It can also use this state to detect changes to the header and thus restart the corresponding worker, freeing its imports.

TODO(WN): We may eventually want to keep track of approximately (since this isn't knowable exactly) where in the file a worker crashed. Then on restart, we tell said worker to only parse up to that point and query the user about how to proceed (continue OR allow the user to fix the bug and then continue OR ..). Without this, if the crash is deterministic, users may be confused about why the server seemingly stopped working for a single file.

Watchdog <-> worker communication #

The watchdog process and its file worker processes communicate via LSP. If the necessity arises, we might add non-standard commands similarly based on JSON-RPC. Most requests and notifications are forwarded to the corresponding file worker process, with the exception of these notifications:

• textDocument/didOpen: Launch the file worker, create the associated watchdog state and launch a task to asynchronously receive LSP packets from the worker (e.g. request responses).
• textDocument/didChange: Update the local file state. If the header was mutated, signal a shutdown to the file worker by closing the I/O channels. Then restart the file worker. Otherwise, forward the didChange notification.
• textDocument/didClose: Signal a shutdown to the file worker and remove the associated watchdog state.

Moreover, we don't implement the full protocol at this level:

• Upon starting, the initialize request is forwarded to the worker, but it must not respond with its server capabilities. Consequently, the watchdog will not send an initialized notification to the worker.
• After initialize, the watchdog sends the corresponding didOpen notification with the full current state of the file. No additional didOpen notifications will be forwarded to the worker process.
• $/cancelRequest notifications are forwarded to all file workers.
• File workers are always terminated with an exit notification, without previously receiving a shutdown request. Similarly, they never receive a didClose notification.

Watchdog <-> client communication #

The watchdog itself should implement the LSP standard as closely as possible. However we reserve the right to add non-standard extensions in case they're needed, for example to communicate tactic state.