Use supported_features=['debugger'] in kernel info reply (#1296)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

ipykernel/kernelbase.py

@@ -880,18 +880,23 @@ async def connect_request(self, socket, ident, parent):
 
     @property
     def kernel_info(self):
-        info = {
+        from .debugger import _is_debugpy_available
+
+        supported_features: list[str] = []
+        if self._supports_kernel_subshells:
+            supported_features.append("kernel subshells")
+        if _is_debugpy_available:
+            supported_features.append("debugger")
+
+        return {
             "protocol_version": kernel_protocol_version,
             "implementation": self.implementation,
             "implementation_version": self.implementation_version,
             "language_info": self.language_info,
             "banner": self.banner,
             "help_links": self.help_links,
-            "supported_features": [],
+            "supported_features": supported_features,
         }
-        if self._supports_kernel_subshells:
-            info["supported_features"] = ["kernel subshells"]
-        return info
 
     async def kernel_info_request(self, socket, ident, parent):
         """Handle a kernel info request."""

tests/test_debugger.py

@@ -96,6 +96,17 @@ def test_debug_initialize(kernel):
         assert reply == {}
 
 
+def test_supported_features(kernel_with_debug):
+    kernel_with_debug.kernel_info()
+    reply = kernel_with_debug.get_shell_msg(timeout=TIMEOUT)
+    supported_features = reply["content"]["supported_features"]
+
+    if debugpy:
+        assert "debugger" in supported_features
+    else:
+        assert "debugger" not in supported_features
+
+
 def test_attach_debug(kernel_with_debug):
     reply = wait_for_debug_request(
         kernel_with_debug, "evaluate", {"expression": "'a' + 'b'", "context": "repl"}