LSP: Handle shutdown commands

This fixes the issue with terminal-based editor Helix which asks
language servers to shut down when trying to close the editor. Since
blueprint-compiler's server implementation didn't handle this request,
Helix ended up waiting for a response until timing out after a few
seconds and forcefully terminating the language server process.

Besides fixing Helix, this patch should also make user-initiated server
restarts more robust.

blueprintcompiler/lsp.py

@@ -118,6 +118,7 @@ class LanguageServer:
         self.client_capabilities = {}
         self.client_supports_completion_choice = False
         self._open_files: T.Dict[str, OpenFile] = {}
+        self._exited = False
 
     def run(self):
         # Read <doc> tags from gir files. During normal compilation these are
@@ -125,7 +126,7 @@ class LanguageServer:
         xml_reader.PARSE_GIR.add("doc")
 
         try:
-            while True:
+            while not self._exited:
                 line = ""
                 content_len = -1
                 while content_len == -1 or (line != "\n" and line != "\r\n"):
@@ -221,6 +222,14 @@ class LanguageServer:
             },
         )
 
+    @command("shutdown")
+    def shutdown(self, id, params):
+        self._send_response(id, None)
+
+    @command("exit")
+    def exit(self, id, params):
+        self._exited = True
+
     @command("textDocument/didOpen")
     def didOpen(self, id, params):
         doc = params.get("textDocument")