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.

CHANGELOG.md

@@ -45,6 +45,7 @@ Status of the `main` branch. Changes prior to the next official version change w
   - Fix: `rename_symbol` for Vue files now correctly propagates edits to the TypeScript server, enabling cross-file renames in `.vue` files 
   - Fix: Lean4 stale cache — empty document symbol responses (returned before `lake build` completes) are no longer persisted, preventing symbols from being permanently hidden #1356
   - Add JSON language server support via `vscode-json-languageserver` (experimental) #1391
+  - Fix: Elixir/Expert deadlock on startup — Expert's build pipeline requires a `textDocument/didOpen` notification to start; Serena now opens `mix.exs` immediately after `initialized` so Expert begins compiling instead of waiting indefinitely #1397
 
 Dashboard:
   - Add configurable dashboard interface mode (new global configuration setting `web_dashboard_interface`):

src/solidlsp/language_servers/elixir_tools/elixir_tools.py

@@ -360,6 +360,28 @@ class ElixirTools(SolidLanguageServer):
 
         self.server.notify.initialized({})
 
+        # Expert's build pipeline is triggered by a textDocument/didOpen notification.
+        # Without it Expert sits idle and never emits the $/progress signals we wait for,
+        # causing a deadlock. Opening mix.exs is the minimal trigger; we close it again
+        # once the server is ready so it does not linger in the open-file set.
+        mix_exs_path = os.path.join(self.repository_root_path, "mix.exs")
+        mix_exs_uri = pathlib.Path(mix_exs_path).as_uri() if os.path.exists(mix_exs_path) else None
+
+        if mix_exs_uri is not None:
+            with open(mix_exs_path, encoding="utf-8") as f:
+                mix_exs_content = f.read()
+            self.server.notify.did_open_text_document(
+                {
+                    "textDocument": {
+                        "uri": mix_exs_uri,
+                        "languageId": "elixir",
+                        "version": 1,
+                        "text": mix_exs_content,
+                    }
+                }
+            )
+            log.debug("Opened mix.exs to trigger Expert's build pipeline")
+
         # Expert needs time to compile the project and build indexes on first run.
         # This can take 2-3+ minutes for mid-sized codebases.
         # After the first run, subsequent startups are much faster.
@@ -370,3 +392,7 @@ class ElixirTools(SolidLanguageServer):
         else:
             log.warning(f"Expert did not signal readiness within {ready_timeout}s. Proceeding with requests anyway.")
             self.server_ready.set()  # Mark as ready anyway to allow requests
+
+        if mix_exs_uri is not None:
+            self.server.notify.did_close_text_document({"textDocument": {"uri": mix_exs_uri}})
+            log.debug("Closed mix.exs after Expert is ready")

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()