[code] Don't start the language client unless there is an active edit…

…or for us

This seems like the right setup, making the server start lazy.

Still it would be better that VSCode API allowed us to activate our
extension in a more fine-grained fashion.

Fixes #750

CHANGES.md

@@ -26,6 +26,9 @@
    it is often not perfect. (@ejgallego, #762, fixes #317)
  - [lsp] [hover] Show full name and provenance of identifiers
    (@ejgallego, #762)
+ - [code] Don't start server on extension activation, unless an editor
+   we own is active. We also auto-start the server if a document that
+   we own is opened later (@ejgallego, #758, fixes #750)
 
 # coq-lsp 0.1.10: Hasta el 40 de Mayo _en effect_...
 ----------------------------------------------------

editor/code/src/client.ts

@@ -460,7 +460,7 @@ export function activateCoqLSP(
       0
     );
     lspStatusItem.command = "coq-lsp.toggle";
-    lspStatusItem.text = "coq-lsp (activating)";
+    lspStatusItem.text = "coq-lsp (not active)";
     lspStatusItem.show();
     context.subscriptions.push(lspStatusItem);
   };
@@ -521,7 +521,22 @@ export function activateCoqLSP(
 
   createEnableButton();
 
-  start();
+  // Fix for bug #750
+  //
+  // XXX we need to keep an eye to start the client if a buffer that
+  // belongs to us is open.
+  const active_editors_for_us = (editors: readonly TextEditor[]) =>
+    editors.some(
+      (editor) => languages.match(CoqSelector.all, editor.document) > 0
+    );
+
+  window.onDidChangeVisibleTextEditors((editors) => {
+    if (!client || !client.isRunning()) {
+      if (active_editors_for_us(editors)) start();
+    }
+  }, context.subscriptions);
+
+  if (active_editors_for_us(window.visibleTextEditors)) start();
 
   return {
     goalsRequest: (params) => {