Bug/Feature Request: Allow configurable error reporting levels for partial LSP compatibility

[Zim-Inn]

Description:

Currently, when a language server (e.g. Haskell Language Server) returns responses that include newer or partially unsupported LSP extensions (such as textDocument/inlayHint or importLens), LSP4IJ throws a ResponseErrorException and stops consuming the response. This behavior prevents the IDE plugin from continuing to provide other available services, even if most of the protocol is still compatible.

Problem:

• Strict error handling causes the entire language server integration to fail when encountering one unsupported feature.
• Users lose access to otherwise functional features (completion, diagnostics, hover, etc.).
• This is especially problematic for fast-evolving language servers (e.g. HLS) that adopt new LSP extensions ahead of client support.

Proposal:
Introduce a configurable error reporting level in LSP4IJ, for example:

• Strict (default): current behavior, fail on any protocol mismatch.
• Warn: log the error, show a warning to the user, but continue consuming other responses.
• Silent: ignore unsupported responses, continue with available features.

Benefits:

• Improves resilience of LSP4IJ-based plugins against evolving language servers.
• Allows users to continue working with partially compatible servers.
• Provides flexibility for plugin developers and end users to choose the desired balance between strictness and usability.

Suggested Implementation:

• Add a configuration option (e.g. in plugin settings or via API) to set error reporting level.
• Wrap JSON-RPC response handling with a try/catch that respects the configured level.
• Ensure warnings are logged in IDE event log for transparency.

Example Use Case:
With Haskell Language Server, importLens may fail due to rule mismatch, but other features (completion, diagnostics) remain usable. Under "Warn" mode, the plugin would log the error but continue providing those features.

[angelozerr]

To be honnest with you I dont understand your issue. LSP4IJ checks the server capability and if server has the proper server capabilty it consumes the lsp request.

The ResponseErrorException is thrown when server throws an exception. It is not lsp4ij which throws this error.

If some lsp feature like inlayHint fails it doesnt fail other lsp requests like completion, etc

[Zim-Inn]

some lsp feature like inlayHint fails it doesnt fail other lsp requests like completion, etc

yes, i got it. i mean that it is huge noise in IDEA, because the error window pop up

[angelozerr]

By default you have a popup error but you can disable it, right?

[Zim-Inn]

That just work on ballon pop. But on the scene of plugin's unhandle exception, it will pop again when i dismiss it. zim ***@***.***

[angelozerr]

Could you explain me how to reproduce your issue please.

[Zim-Inn]

IDEA version: 2025.2.5 HLS version: recommend ghc version: recommend plugin based on LSP4IJ: Haskell lsp  file: Main.hs in a simple `cabal init --minimal` project user action: config the haskell plugin and restart the project. Then type any char in the file  zim ***@***.***