Bugfix in tool calling with role tool

Author: lhoet-google

x-pack/plugin/inference/src/main/java/org/elasticsearch/xpack/inference/services/googlevertexai/request/GoogleVertexAiUnifiedChatCompletionRequestEntity.java

@@ -10,6 +10,7 @@
 import org.elasticsearch.ElasticsearchStatusException;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.common.xcontent.LoggingDeprecationHandler;
+import org.elasticsearch.core.Nullable;
 import org.elasticsearch.inference.UnifiedCompletionRequest;
 import org.elasticsearch.rest.RestStatus;
 import org.elasticsearch.xcontent.ToXContentObject;
@@ -60,6 +61,7 @@ public class GoogleVertexAiUnifiedChatCompletionRequestEntity implements ToXCont
     private static final String MODEL_ROLE = "model";
     private static final String ASSISTANT_ROLE = "assistant";
     private static final String SYSTEM_ROLE = "system";
+    private static final String TOOL_ROLE = "tool";
     private static final String STOP_SEQUENCES = "stopSequences";
 
     private static final String SYSTEM_INSTRUCTION = "systemInstruction";
@@ -76,6 +78,9 @@ private String messageRoleToGoogleVertexAiSupportedRole(String messageRole) {
         } else if (messageRole.equals(ASSISTANT_ROLE)) {
             // Gemini VertexAI API does not use "assistant". Instead, it uses "model"
             return MODEL_ROLE;
+        } else if (messageRole.equals(TOOL_ROLE)) {
+            // Gemini VertexAI does not have the tool role, so we map it to "model"
+            return MODEL_ROLE;
         }
 
         var errorMessage = format(

x-pack/plugin/inference/src/test/java/org/elasticsearch/xpack/inference/services/googlevertexai/request/GoogleVertexAiUnifiedChatCompletionRequestEntityTests.java

@@ -447,46 +447,53 @@ public void testError_UnsupportedContentObjectType() throws IOException {
     public void testParseAllFields() throws IOException {
         String requestJson = """
             {
-                "contents": [
+              "contents": [
+                {
+                  "role": "user",
+                  "parts": [
                     {
-                        "role": "user",
-                        "parts": [
-                            { "text": "some text" },
-                            { "functionCall" : {
-                                "name": "get_delivery_date",
-                                "args": {
-                                    "order_id" : "order_12345"
-                                    }
-                                }
-                            }
-                        ]
-                    }
-                ],
-                "generationConfig": {
-                    "stopSequences": ["stop"],
-                    "temperature": 0.1,
-                    "maxOutputTokens": 100,
-                    "topP": 0.2
-                },
-                "tools": [
+                      "text": "some text"
+                    },
                     {
-                        "functionDeclarations": [
-                            {
-                                "name": "get_current_weather",
-                                "description": "Get the current weather in a given location",
-                                "parameters": {
-                                    "type": "object"
-                                }
-                            }
-                        ]
+                      "functionCall": {
+                        "name": "get_delivery_date",
+                        "args": {
+                          "order_id": "order_12345"
+                        }
+                      }
                     }
+                  ]
+                }
+              ],
+              "generationConfig": {
+                "stopSequences": [
+                  "stop"
                 ],
-                "toolConfig": {
-                    "functionCallingConfig" : {
-                        "mode": "ANY",
-                        "allowedFunctionNames": [ "some function" ]
+                "temperature": 0.1,
+                "maxOutputTokens": 100,
+                "topP": 0.2
+              },
+              "tools": [
+                {
+                  "functionDeclarations": [
+                    {
+                      "name": "get_current_weather",
+                      "description": "Get the current weather in a given location",
+                      "parameters": {
+                        "type": "object"
+                      }
                     }
+                  ]
                 }
+              ],
+              "toolConfig": {
+                "functionCallingConfig": {
+                  "mode": "ANY",
+                  "allowedFunctionNames": [
+                    "some function"
+                  ]
+                }
+              }
             }
             """;
 
@@ -561,7 +568,7 @@ public void testParseFunctionCallNoContent() throws IOException {
             List.of(
                 new UnifiedCompletionRequest.Message(
                     null,
-                    "assistant",
+                    "tool",
                     "100",
                     List.of(
                         new UnifiedCompletionRequest.ToolCall(