Fix invalid request 400, for tool calls with nil arguments failing when using Anthropic models via GitHub Copilot.

Fixes #340

Author: ericdallo

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ## Unreleased
 
+- Fix invalid request 400, for tool calls with nil arguments failing when using Anthropic models via GitHub Copilot. #340
+
 ## 0.109.2
 
 - Add `chat/clear` message.

src/eca/llm_providers/openai.clj

@@ -100,7 +100,7 @@
             "tool_call" {:type "function_call"
                          :name (:full-name content)
                          :call_id (:id content)
-                         :arguments (json/generate-string (:arguments content))}
+                         :arguments (json/generate-string (or (:arguments content) {}))}
             "tool_call_output"
             {:type "function_call_output"
              :call_id (:id content)

src/eca/llm_providers/openai_chat.clj

@@ -168,7 +168,7 @@
                    :tool_calls [(cond-> {:id       tool-call-id
                                          :type     "function"
                                          :function {:name      (:full-name content)
-                                                    :arguments (json/generate-string (:arguments content))}}
+                                                    :arguments (json/generate-string (or (:arguments content) {}))}}
                                  ;; Preserve Google Gemini thought signatures if present
                                   (:external-id content)
                                   (assoc-in [:extra_content :google :thought_signature]

test/eca/llm_providers/openai_chat_test.clj

@@ -146,6 +146,22 @@
           thinking-start-tag
           thinking-end-tag))))
 
+  (testing "Tool call transformation with nil arguments defaults to empty object"
+    (is (match?
+         {:role "assistant"
+          :tool_calls [{:id "call-123"
+                        :type "function"
+                        :function {:name "foo__diagnostics"
+                                   :arguments "{}"}}]}
+         (#'llm-providers.openai-chat/transform-message
+          {:role "tool_call"
+           :content {:id "call-123"
+                     :full-name "foo__diagnostics"
+                     :arguments nil}}
+          true
+          thinking-start-tag
+          thinking-end-tag))))
+
   (testing "Tool call transformation prefers :llm-tool-call-id when present"
     (is (match?
          {:role "assistant"

test/eca/llm_providers/openai_test.clj

@@ -150,4 +150,15 @@
                                                                     :error false
                                                                     :text "Allowed directories: /foo/bar"}]}}}
            {:role "assistant" :content [{:type :text :text "I see /foo/bar"}]}]
+          true))))
+  (testing "With tool_call with nil arguments defaults to empty object"
+    (is (match?
+         [{:role "user" :content [{:type "input_text" :text "Check diagnostics"}]}
+          {:type "function_call"
+           :call_id "call-1"
+           :name "eca__editor_diagnostics"
+           :arguments "{}"}]
+         (#'llm-providers.openai/normalize-messages
+          [{:role "user" :content [{:type :text :text "Check diagnostics"}]}
+           {:role "tool_call" :content {:id "call-1" :full-name "eca__editor_diagnostics" :arguments nil}}]
           true)))))