fix: report unavailable LSP servers explicitly

index.ts

@@ -18,8 +18,28 @@ import {
   UnsupportedExtensionError,
 } from "./src/types.ts";
 
+type LspUnavailable = { piLspUnavailable: true; message: string };
+
+function lspUnavailable(message: string): LspUnavailable {
+  return { piLspUnavailable: true, message };
+}
+
+function isLspUnavailable(result: unknown): result is LspUnavailable {
+  return Boolean(
+    result &&
+      typeof result === "object" &&
+      "piLspUnavailable" in result &&
+      (result as { piLspUnavailable?: unknown }).piLspUnavailable === true,
+  );
+}
+
+function formatUnavailable(result: LspUnavailable): string {
+  return `(LSP unavailable: ${result.message})`;
+}
+
 // Format Hover - Turn an LSP hover response into readable text.
 function formatHover(result: unknown): string {
+  if (isLspUnavailable(result)) return formatUnavailable(result);
   if (!result || typeof result !== "object") return "(no hover info)";
   const hover = result as { contents?: unknown };
   if (!hover.contents) return "(empty)";
@@ -49,6 +69,7 @@ function formatHover(result: unknown): string {
 
 // Format Definition - Turn definition locations into readable text.
 function formatDefinition(result: unknown): string {
+  if (isLspUnavailable(result)) return formatUnavailable(result);
   if (!result) return "(no definition found)";
   const locations = Array.isArray(result) ? result : [result];
   if (locations.length === 0) return "(no definition found)";
@@ -64,6 +85,7 @@ function formatDefinition(result: unknown): string {
 
 // Format References - Turn reference locations into readable text.
 function formatReferences(result: unknown): string {
+  if (isLspUnavailable(result)) return formatUnavailable(result);
   if (!result || !Array.isArray(result)) return "(no references found)";
   if (result.length === 0) return "(no references found)";
 
@@ -85,6 +107,7 @@ function formatReferences(result: unknown): string {
 
 // Format Completions - Turn completion items into readable text.
 function formatCompletions(result: unknown): string {
+  if (isLspUnavailable(result)) return formatUnavailable(result);
   if (!result) return "(no completions)";
 
   // Resolve to CompletionItem[] if it's a CompletionList
@@ -150,6 +173,7 @@ function formatCompletions(result: unknown): string {
 
 // Format Document Symbols - Turn symbols into a tree outline.
 function formatDocumentSymbols(result: unknown): string {
+  if (isLspUnavailable(result)) return formatUnavailable(result);
   if (!result || !Array.isArray(result)) return "(no symbols)";
   const symbols = result as any[];
   if (symbols.length === 0) return "(no symbols)";
@@ -235,6 +259,7 @@ function formatServerDiagnostics(diags: any[], limit: number): string {
 // { [serverId]: { uri, diagnostics[] } }. Single-server results omit the
 // header to avoid noise.
 function formatDiagnostics(result: unknown, limit = 20): string {
+  if (isLspUnavailable(result)) return formatUnavailable(result);
   if (!result || typeof result !== "object") return "(no diagnostics)";
 
   const grouped = result as Record<string, any>;
@@ -275,6 +300,34 @@ function isExpectedError(error: unknown): boolean {
   );
 }
 
+function unavailableForFile(filePath: string, includeDiagnosticsOnly = false): LspUnavailable {
+  const ext = path.extname(filePath).replace(/^\./, "");
+  const label = ext ? `.${ext}` : "files without an extension";
+  const matches = getServersForPath(filePath).filter((server) =>
+    server.match.includes(ext) && (includeDiagnosticsOnly || !server.diagnosticsOnly)
+  );
+
+  if (matches.length === 0) {
+    return lspUnavailable(`no LSP server is registered for ${label}`);
+  }
+
+  const disabled = matches.filter((server) => disabledServers.has(server.id));
+  if (disabled.length === matches.length) {
+    return lspUnavailable(
+      `matching LSP server(s) are disabled: ${disabled.map((s) => s.id).join(", ")}`,
+    );
+  }
+
+  const unavailable = matches.filter((server) => !isServerAvailable(server));
+  if (unavailable.length > 0) {
+    return lspUnavailable(
+      `matching LSP server(s) are not on PATH: ${unavailable.map((s) => s.command).join(", ")}`,
+    );
+  }
+
+  return lspUnavailable(`no applicable LSP server is available for ${label}`);
+}
+
 // Disabled Servers - In-memory set of disabled server IDs. Scoped to this
 // extension process; the shared daemon is never mutated by disable/enable.
 const lspToolNames = [
@@ -301,14 +354,12 @@ async function runLsp(
     // touching the daemon so other pi instances sharing it are unaffected.
     const server = pickServer(filePath);
     if (disabledServers.has(server.id)) {
-      throw new Error(
-        `LSP server "${server.id}" is disabled. Use /lsp-enable ${server.id} to re-enable.`,
-      );
+      return unavailableForFile(filePath);
     }
     return await daemonRequest(filePath, server.id, method, params);
   } catch (error) {
     if (isExpectedError(error)) {
-      return undefined;
+      return unavailableForFile(filePath);
     }
     // Daemon-wrapped errors (plain Error with expected message) are also
     // expected — the daemon catches pickServer() throws and returns them
@@ -318,7 +369,7 @@ async function runLsp(
       (error.message.includes("No LSP server registered") ||
         error.message.includes("not found on PATH"))
     ) {
-      return undefined;
+      return unavailableForFile(filePath);
     }
     throw error;
   }
@@ -347,22 +398,22 @@ function withTimeout<T>(promise: Promise<T>, ms: number): Promise<T> {
 }
 
 // Run LSP Diagnostics - Fans out to all matching servers in a single
-// daemon call. Returns the grouped result map or undefined if no servers.
+// daemon call. Returns an explicit unavailable result if no server applies.
 async function runDiagnostics(filePath: string): Promise<unknown> {
   try {
     const serverIds = pickDiagnosticServers(filePath);
-    if (serverIds.length === 0) return undefined;
+    if (serverIds.length === 0) return unavailableForFile(filePath, true);
     return await daemonDiagnostics(filePath, serverIds, 1500);
   } catch (error) {
     if (isExpectedError(error)) {
-      return undefined;
+      return unavailableForFile(filePath, true);
     }
     if (
       error instanceof Error &&
       (error.message.includes("No LSP server registered") ||
         error.message.includes("not found on PATH"))
     ) {
-      return undefined;
+      return unavailableForFile(filePath, true);
     }
     throw error;
   }
@@ -572,6 +623,7 @@ export default function (pi: ExtensionAPI) {
       // Run LSP diagnostics with timeout - Prevent the auto-check hook from
       // blocking pi if the daemon or LSP server is slow or unresponsive.
       const result = await withTimeout(runDiagnostics(absolutePath), 3000);
+      if (isLspUnavailable(result)) return;
       const formatted = formatDiagnostics(result, 10);
 
       // Only send a message if there are actual diagnostics