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LSP Inline Diagnostics

Task 26 — Wire the LSP client to surface publishDiagnostics results in the editor with inline squiggles, hover tooltips, incremental document sync, and status bar counts.

Architecture

LSP server stdout
  → spawn_stdout_reader (background thread, JSON-RPC framing)
  → StdoutMsg::Message(Value) via mpsc channel
  → worker_main dispatches to handle_server_message()
  → handle_publish_diagnostics() converts to DiagnosticEntry vec
  → LspManagerEvent::Diagnostics sent to UI thread
  → handle_lsp_events() stores in AppState.diagnostics (DiagnosticMap)
  → FerriteEditor reads diagnostics via EditorWidget builder
  → render_diagnostic_squiggles() draws wavy underlines
  → Hover tooltip shows message at pointer position

Data Structures

DiagnosticEntry (src/lsp/state.rs)

pub struct DiagnosticEntry {
    pub start_line: usize,   // 0-indexed
    pub start_col: usize,
    pub end_line: usize,
    pub end_col: usize,
    pub severity: DiagnosticSeverity,  // Error | Warning | Information | Hint
    pub message: String,
    pub source: Option<String>,
}

DiagnosticMap (src/lsp/state.rs)

HashMap<PathBuf, Vec<DiagnosticEntry>> with convenience methods:

Method Description
set(path, entries) Replace diagnostics for a file
get(path) Get diagnostics for a file
for_line_range(path, start, end) Filter to visible line range
counts() Sum (errors, warnings) across all files
clear() Remove all diagnostics

LSP Protocol Integration

Handshake (src/lsp/manager.rs)

Task 26 implements the full LSP initialize/initialized handshake:

  1. send_initialize() — sends initialize request with client capabilities (sync = full, diagnostics)
  2. Server responds → handle_server_message() sets server.initialized = true
  3. send_initialized() — sends empty initialized notification

Document Sync

Full-text sync (TextDocumentSyncKind::Full):

Notification When Source
textDocument/didOpen Tab becomes active + server is Ready sync_active_doc_to_lsp()
textDocument/didChange last_edit_time changes (debounced 300ms) sync_active_doc_to_lsp()
textDocument/didClose Not yet wired (future enhancement)

Tracking state lives on FerriteApp:

  • lsp_opened_docs: HashSet<PathBuf> — normalized paths already sent didOpen
  • lsp_doc_versions: HashMap<PathBuf, i32> — version counter per path
  • lsp_last_edit_times: HashMap<PathBuf, Instant> — snapshot of Tab::last_edit_time at last sync
  • lsp_last_change_sent: HashMap<PathBuf, Instant> — debounce: when last didChange was sent

Path normalization: All path keys are normalized via normalize_lsp_path() (uppercased drive letter on Windows, \\?\ prefix stripped) so that URIs from the server and filesystem paths from tabs always match.

Diagnostics Flow

Server sends textDocument/publishDiagnostics → handle_publish_diagnostics():

  1. Converts URI to PathBuf via uri_to_path()
  2. Parses each JSON diagnostic into DiagnosticEntry
  3. Sends LspManagerEvent::Diagnostics to UI thread

handle_lsp_events() in file_ops.rs calls self.state.diagnostics.set(path, entries).

Rendering

Squiggles (src/editor/ferrite/highlights.rs)

render_diagnostic_squiggles() draws wavy underlines for diagnostics overlapping visible lines:

  • Error → red squiggle
  • Warning → yellow/orange squiggle
  • Info/Hint → blue squiggle (dark) / darker blue (light)

The squiggle is drawn as a series of connected line segments forming a sine-wave pattern with amplitude 2px and period 4px, positioned at the baseline of the text.

Only diagnostics overlapping the visible line range (start_line..end_line) are processed.

Hover Tooltips (src/editor/ferrite/editor.rs)

When the pointer hovers over the editor area:

  1. Convert pointer position to buffer cursor via pos_to_cursor()
  2. Check each diagnostic with cursor_in_diagnostic_range()
  3. Show egui::show_tooltip_at_pointer with severity icon + message

Status Bar (src/app/status_bar.rs)

Displays error/warning counts next to the LSP status line:

  • Red label for errors: "N err"
  • Yellow label for warnings: "N warn"
  • Only shown when counts > 0

Helper Functions (src/lsp/mod.rs)

Function Description
normalize_lsp_path(path) Normalize path for diagnostic map keys (uppercase drive, strip \\?\)
path_to_uri(path) Convert PathBuf to file:// URI (normalizes first, handles Windows)
language_id_for_path(path) Map extension to LSP languageId (rust, python, go, etc.)

Key Files

File Changes
src/lsp/state.rs DiagnosticSeverity, DiagnosticEntry, DiagnosticMap
src/lsp/manager.rs Full stdout read loop, initialize handshake, didOpen/didChange/didClose, publish diagnostics handling
src/lsp/mod.rs path_to_uri(), language_id_for_path(), re-exports
src/state.rs AppState.diagnostics: DiagnosticMap field
src/app/mod.rs lsp_opened_docs, lsp_doc_versions, lsp_content_hashes tracking fields
src/app/file_ops.rs handle_lsp_events() → Diagnostics variant, sync_active_doc_to_lsp()
src/app/central_panel.rs Pass tab_diagnostics to EditorWidget
src/editor/widget.rs diagnostics field + builder method on EditorWidget
src/editor/ferrite/editor.rs diagnostics field, hover tooltip logic
src/editor/ferrite/highlights.rs render_diagnostic_squiggles(), draw_squiggle(), cursor_in_diagnostic_range()
src/app/status_bar.rs Error/warning count display

Testing

  1. Open a Rust workspace with rust-analyzer installed
  2. Introduce a syntax error (e.g., remove a semicolon)
  3. Verify: red squiggle appears under the error
  4. Hover over squiggle → tooltip shows diagnostic message
  5. Fix the error → squiggle disappears after server re-analyzes
  6. Status bar shows error/warning counts