fix(nix): use published diagnostics for nixd

CHANGELOG.md

@@ -35,6 +35,8 @@ Status of the `main` branch. Changes prior to the next official version change w
     project creation) 
   - Add `python_basedpyright` as an alternative Python language server
   - Nix/nixd: support custom `ls_path` launchers and external JSON settings through `config_path` #1737
+  - Fix: Nix/nixd diagnostics now use published diagnostics instead of the unsupported
+    `textDocument/diagnostic` request, which terminated nixd #1802
   - Fix: `get_diagnostics_for_file` crashed with `SolidLSPException` for any Ansible file with at least
     one lint finding, because `ansible-language-server` doesn't implement `textDocument/documentSymbol`
     and the request used to map diagnostics onto owning symbols just threw. `AnsibleLanguageServer` now

src/solidlsp/language_servers/nixd_ls.py

@@ -378,6 +378,12 @@ class NixLanguageServer(SolidLanguageServer):
         }
         return initialize_params
 
+    @override
+    def _supports_pull_diagnostics(self) -> bool:
+        # nixd publishes diagnostics after textDocument/didOpen but terminates when it receives
+        # textDocument/diagnostic. Force the published-diagnostics path instead.
+        return False
+
     def _start_server(self):
         """Start nixd server process"""
         initialize_params = self._create_initialize_params()

test/solidlsp/nix/test_nix_basic.py

@@ -259,3 +259,4 @@ class TestNixLanguageServer:
             (),
             min_count=1,
         )
+        assert language_server.is_running()