noisy `-32801` ("Content Modified") errors

[justinmk]

How are you using the lua-language-server?

NeoVim

Which OS are you using?

MacOS

What is the issue affecting?

Other

Expected Behaviour

In the request-completion path, when the server has computed a result against document version V, return that result regardless of whether didChange for V+1 (or later) has since arrived. Only return -32801 if the document
modification was genuinely external / out-of-band — which is rare in normal usage and not what didChange represents.

If pre-empting in-flight requests on didChange is desired as an optimization, the spec-compliant signal is for the client to send $/cancelRequest. The server should not unilaterally short-circuit valid in-flight work with -32801.

Per the spec, the client is supposed to handle staleness via cancellation. With lua-language-server pre-empting that decision and erroring instead:

• Clients that handle -32801 strictly as an error end up logging spurious errors (cf. neovim/neovim#40208).
• Clients that could have used the older-version result (perfectly valid per the spec — "even computed on an older state might still be useful") never get the chance.
• Clients that wanted to cancel can no longer rely on $/cancelRequest semantics because the server has already aborted on its own initiative.

Actual Behaviour

Sending a fast sequence of didChanges while semantic-tokens requests are in flight causes the server to error every in-flight request with:

{ "code": -32801, "message": "Content modified." }

even though the modification was delivered through normal didChange notifications, not "outside normal conditions."

Reproduction steps

1. Open a Lua file in any LSP-capable editor that requests semanticTokens/full (e.g. Neovim 0.12+).
2. Start typing across multiple lines, fast enough that successive didChange notifications outpace the server's processing.
3. Observe: every in-flight semantic-tokens request comes back with -32801 Content modified. instead of a (possibly stale) result.

Additional Notes

lua-language-server returns LSP error -32801 ("Content Modified") in response to textDocument/semanticTokens/full (and likely other requests) whenever a textDocument/didChange notification arrives before the response is sent.
This contradicts the LSP specification, which explicitly forbids using -32801 for content changes detected in unprocessed messages — i.e. for the exact case currently being signaled.

What the spec says:

LSP §responseError.code (specifically the ContentModified = -32801 entry):

The server detected that the content of a document got modified outside normal conditions. A server should NOT send this error code if it detects a content change in its unprocessed messages. The result even computed on an older
state might still be useful for the client.

If a client decides that a result is not of any use anymore the client should cancel the request.

So the intended semantics are:

• -32801 is for "out-of-band" content modification (e.g., the file on disk changed in a way the server can't reconcile with its in-flight state).

Log File

No response