Fix: 1397 Expert deadlock by sending didOpen(mix.exs) before readiness wait (#1405)

* Fix: Expert deadlock by sending didOpen(mix.exs) before readiness wait

Expert's build pipeline only starts after receiving a textDocument/didOpen
notification. Without it, Serena waited 300 s for $/progress signals that
Expert never emitted, causing a deadlock on every cold start.

test/solidlsp/elixir/test_elixir_startup.py

@@ -0,0 +1,104 @@
+"""Unit tests for Elixir Expert language server startup behavior."""
+
+import threading
+from unittest.mock import MagicMock
+
+from solidlsp.language_servers.elixir_tools.elixir_tools import ElixirTools
+
+
+def _make_elixir_tools(tmp_path):
+    language_server = object.__new__(ElixirTools)
+    language_server.repository_root_path = str(tmp_path)
+    language_server.server_ready = threading.Event()
+    language_server.request_id = 0
+    return language_server
+
+
+def _make_mock_server():
+    server = MagicMock()
+    server.send.initialize.return_value = {"capabilities": {"textDocumentSync": {}}}
+    return server
+
+
+class TestElixirToolsStartup:
+    """Tests for ElixirTools._start_server() startup behavior — the Expert deadlock fix."""
+
+    def test_sends_did_open_for_mix_exs_after_initialized(self, tmp_path):
+        """Expert blocks waiting for a didOpen notification to trigger its build pipeline."""
+        (tmp_path / "mix.exs").write_text("defmodule App.MixProject do\n  use Mix.Project\nend\n", encoding="utf-8")
+
+        language_server = _make_elixir_tools(tmp_path)
+        server = _make_mock_server()
+        language_server.server = server
+        language_server.server_ready.set()
+
+        language_server._start_server()
+
+        calls = server.notify.did_open_text_document.call_args_list
+        assert len(calls) == 1, f"Expected one didOpen notification for mix.exs, got {len(calls)}"
+        text_doc = calls[0][0][0]["textDocument"]
+        assert text_doc["uri"].endswith("mix.exs"), f"Expected mix.exs URI, got {text_doc['uri']}"
+        assert text_doc["languageId"] == "elixir"
+
+    def test_did_open_contains_mix_exs_content(self, tmp_path):
+        """The didOpen notification must include the file content so Expert can parse it."""
+        content = "defmodule App.MixProject do\n  use Mix.Project\nend\n"
+        (tmp_path / "mix.exs").write_text(content, encoding="utf-8")
+
+        language_server = _make_elixir_tools(tmp_path)
+        server = _make_mock_server()
+        language_server.server = server
+        language_server.server_ready.set()
+
+        language_server._start_server()
+
+        calls = server.notify.did_open_text_document.call_args_list
+        assert len(calls) == 1
+        text_doc = calls[0][0][0]["textDocument"]
+        assert text_doc["text"] == content
+
+    def test_closes_mix_exs_after_server_ready(self, tmp_path):
+        """mix.exs is closed after Expert signals readiness so it does not linger open."""
+        (tmp_path / "mix.exs").write_text("defmodule App.MixProject do\n  use Mix.Project\nend\n", encoding="utf-8")
+
+        language_server = _make_elixir_tools(tmp_path)
+        server = _make_mock_server()
+        language_server.server = server
+        language_server.server_ready.set()
+
+        language_server._start_server()
+
+        close_calls = server.notify.did_close_text_document.call_args_list
+        assert len(close_calls) == 1, f"Expected one didClose for mix.exs, got {len(close_calls)}"
+        text_doc = close_calls[0][0][0]["textDocument"]
+        assert text_doc["uri"].endswith("mix.exs"), f"Expected mix.exs URI, got {text_doc['uri']}"
+
+    def test_startup_event_order_initialized_then_didopen_then_didclose(self, tmp_path):
+        """Initialized → didOpen(mix.exs) → [ready] → didClose(mix.exs) is the required sequence."""
+        (tmp_path / "mix.exs").write_text("defmodule App.MixProject do\n  use Mix.Project\nend\n", encoding="utf-8")
+
+        events: list[str] = []
+
+        language_server = _make_elixir_tools(tmp_path)
+        server = _make_mock_server()
+        language_server.server = server
+        language_server.server_ready.set()
+
+        server.notify.initialized.side_effect = lambda *_: events.append("initialized")
+        server.notify.did_open_text_document.side_effect = lambda *_: events.append("didOpen")
+        server.notify.did_close_text_document.side_effect = lambda *_: events.append("didClose")
+
+        language_server._start_server()
+
+        assert events == ["initialized", "didOpen", "didClose"], f"Unexpected startup event order: {events}"
+
+    def test_no_crash_when_mix_exs_missing(self, tmp_path):
+        """_start_server must not crash if mix.exs is absent (non-standard project layout)."""
+        language_server = _make_elixir_tools(tmp_path)
+        server = _make_mock_server()
+        language_server.server = server
+        language_server.server_ready.set()
+
+        language_server._start_server()
+
+        server.notify.did_open_text_document.assert_not_called()