fix(language_server): always write to memory file system

[Sysix]

In #15882 we removed the dynamic formatting registration and registered them statically.
LSP Clients could only support static formatting registration and the checks would fail. When someone formats, while not saving, the unsaved changes would disappear.

Removed the checks, so it always saves the content in the file system. Later the Linter will use the file system too when supporting textDocument/diagnostic

[Sysix]

• fix(language_server): always write to memory file system #15975 👈 (View in Graphite)
• main

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[camc314]

Merge activity

• Nov 22, 9:16 PM UTC: The merge label '0-merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Nov 22, 9:16 PM UTC: camc314 added this pull request to the Graphite merge queue.
• Nov 22, 9:21 PM UTC: Merged by the Graphite merge queue.

[Copilot]

Pull request overview

This PR fixes a bug where unsaved file changes would disappear during formatting operations by removing conditional checks for dynamic formatting capability registration. Previously, the language server only maintained an in-memory file system when clients supported dynamic formatting registration, but some LSP clients only support static registration. The fix ensures the in-memory file system is always synchronized with document lifecycle events, preparing for future textDocument/diagnostic support.

Key changes:

• Removed dynamic_formatting field from client capabilities tracking
• Made all in-memory file system operations unconditional across document lifecycle events
• Removed conditional logic from shutdown, did_save, did_change, did_open, and did_close handlers

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
crates/oxc_language_server/src/capabilities.rs	Removed dynamic_formatting field from Capabilities struct and its initialization logic
crates/oxc_language_server/src/backend.rs	Made file system operations unconditional in all document lifecycle event handlers

Comments suppressed due to low confidence (4)

crates/oxc_language_server/src/backend.rs:218

• The doc comment is now outdated. It states the file system is cleared 'if dynamic formatting is enabled', but the code now unconditionally clears the file system. Update to: 'This method clears all diagnostics and the in-memory file system.'

    /// This method clears all diagnostics and the in-memory file system if dynamic formatting is enabled.

crates/oxc_language_server/src/backend.rs:474

• The doc comment is now outdated. It states the file content is updated 'if the client supports dynamic formatting', but the code now unconditionally updates the file system. Update to: 'It will update the in-memory file content.'

    /// It will update the in-memory file content if the client supports dynamic formatting.

crates/oxc_language_server/src/backend.rs:497

• The doc comment is now outdated. It states the file content is added 'if the client supports dynamic formatting', but the code now unconditionally adds to the file system. Update to: 'It will add the in-memory file content.'

    /// It will add the in-memory file content if the client supports dynamic formatting.

crates/oxc_language_server/src/backend.rs:519

• The doc comment is now outdated. It states the file content is removed 'if the client supports dynamic formatting', but the code now unconditionally removes from the file system. Update to: 'It will remove the in-memory file content.'

    /// It will remove the in-memory file content if the client supports dynamic formatting.

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