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LSP On-Demand Server Startup

LSP servers start lazily when the active tab's file extension matches a known language server. This replaces the previous workspace-scan approach that eagerly spawned all detected servers when a workspace opened.

Motivation

Eager startup scanned workspace files (depth 3) on every workspace open and spawned servers for all detected languages — even if the user never opened a file of that type. On-demand startup matches VS Code / Neovim behavior: servers only start when actually needed.

How It Works

Startup Flow

  1. Each frame, handle_lsp_events() calls sync_active_doc_to_lsp().
  2. sync_active_doc_to_lsp() checks the active tab's file extension via detect_lsp_server_for_path().
  3. If no LSP server maps to the extension, nothing happens (e.g. .md files).
  4. If a server is mapped:
    • Disconnected → start_lsp_server_on_demand() spawns it, applying any user overrides from lsp_server_overrides.
    • Starting / Initializing → skip (wait for handshake to complete).
    • Ready → send didOpen / didChange as before.
    • Error → skip (backoff restart in the worker handles crash recovery).
  5. Once the server reaches Ready, the next frame's sync_active_doc_to_lsp() sends didOpen.

Idle Shutdown

When a tab is closed:

  • cleanup_tab_state() sends textDocument/didClose if no other tab shares the same file.
  • Open-document count per server is decremented.
  • When a server's document count reaches 0, a 30-second idle timer starts.
  • check_lsp_idle_shutdown() (called each frame) shuts down servers that have been idle ≥ 30 seconds, setting their status to Disconnected.
  • The server restarts on demand if the user opens another matching file.

Status Bar

The status bar shows only servers that have been started (are known to lsp_status_by_server). It no longer scans the workspace directory each frame. When no servers are running, it shows "LSP" with a hover tooltip explaining on-demand behavior.

Data Structures

Field Type Purpose
lsp_tab_server HashMap<usize, (PathBuf, String)> Maps tab ID → (normalized path, server key) for tabs with an active didOpen
lsp_open_doc_count HashMap<String, usize> Number of open documents per server key
lsp_idle_since HashMap<String, Instant> When a server's doc count dropped to 0

Edge Cases

Scenario Behavior
Multiple tabs, same extension Single shared server; started once
Multiple tabs, same file didOpen sent once; didClose only when all tabs close
Tab closed while server initializing Tab-server mapping not yet created; no didClose needed
Server crash Worker backoff restart handles it; next tab activation triggers didOpen
lsp_enabled = false All tracking maps cleared; sync_active_doc_to_lsp not called
Override path changes All servers stopped; on-demand restart uses new program path
Workspace change All tracking maps cleared; servers restart on demand
Markdown / unknown extension detect_lsp_server_for_path returns None; no server started

Key Files

File What Changed
src/app/file_ops.rs sync_active_doc_to_lsp() — on-demand start; start_lsp_server_on_demand() — helper; check_lsp_idle_shutdown() — idle timer; handle_lsp_events() — simplified toggle/override; lsp_status_bar_text() — no workspace scan
src/app/mod.rs New fields on FerriteApp; cleanup_tab_state() — sends didClose
src/state.rs start_lsp_for_workspace() — now a no-op; removed call from open_workspace()

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