Add support for allowed_function_names (#6273)

A note about `@SerialName("allowed_function_names")`: This is not
strictly necessary, the backend will parse it if it's camel case too. We
should eventually remove all unnecessary `@SerialName` declarations, but
for now, and to keep consistency, I'm adding it to this declaration.

Author: rlazo

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/common/client/Types.kt

@@ -47,7 +47,10 @@ internal data class ToolConfig(
 )
 
 @Serializable
-internal data class FunctionCallingConfig(val mode: Mode) {
+internal data class FunctionCallingConfig(
+  val mode: Mode,
+  @SerialName("allowed_function_names") val allowedFunctionNames: List<String>? = null
+) {
   @Serializable
   enum class Mode {
     @SerialName("MODE_UNSPECIFIED") UNSPECIFIED,

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/internal/util/conversions.kt

@@ -137,7 +137,8 @@ internal fun ToolConfig.toInternal() =
           com.google.firebase.vertexai.common.client.FunctionCallingConfig.Mode.AUTO
         FunctionCallingConfig.Mode.NONE ->
           com.google.firebase.vertexai.common.client.FunctionCallingConfig.Mode.NONE
-      }
+      },
+      functionCallingConfig.allowedFunctionNames
     )
   )
 

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/FunctionCallingConfig.kt

@@ -21,8 +21,11 @@ package com.google.firebase.vertexai.type
  * calling predictions or disable them.
  *
  * @param mode The function calling mode of the model
+ * @param allowedFunctionNames Function names to call. Only set when the [Mode.ANY]. Function names
+ * should match [FunctionDeclaration.name]. With [Mode.ANY], model will predict a function call from
+ * the set of function names provided.
  */
-class FunctionCallingConfig(val mode: Mode) {
+class FunctionCallingConfig(val mode: Mode, val allowedFunctionNames: List<String>? = null) {
 
   /** Configuration for dictating when the model should call the attached function. */
   enum class Mode {

firebase-vertexai/src/main/kotlin/com/google/firebase/vertexai/type/ToolConfig.kt

@@ -27,7 +27,12 @@ class ToolConfig(val functionCallingConfig: FunctionCallingConfig) {
   companion object {
     /** Shorthand to construct a ToolConfig that restricts the model from calling any functions */
     fun never(): ToolConfig = ToolConfig(FunctionCallingConfig(FunctionCallingConfig.Mode.NONE))
-    /** Shorthand to construct a ToolConfig that restricts the model to always call some function */
-    fun always(): ToolConfig = ToolConfig(FunctionCallingConfig(FunctionCallingConfig.Mode.ANY))
+    /**
+     * Shorthand to construct a ToolConfig that restricts the model to always call some function.
+     * You can optionally [allowedFunctionNames] to restrict the model to only call these functions.
+     * See [FunctionCallingConfig] for more information.
+     */
+    fun always(allowedFunctionNames: List<String>? = null): ToolConfig =
+      ToolConfig(FunctionCallingConfig(FunctionCallingConfig.Mode.ANY, allowedFunctionNames))
   }
 }

firebase-vertexai/src/test/java/com/google/firebase/vertexai/common/APIControllerTests.kt

@@ -185,17 +185,21 @@ internal class RequestFormatTests {
             contents = listOf(Content(parts = listOf(TextPart("Arbitrary")))),
             toolConfig =
               ToolConfig(
-                functionCallingConfig =
-                  FunctionCallingConfig(mode = FunctionCallingConfig.Mode.AUTO)
-              ),
-          )
+                FunctionCallingConfig(
+                  mode = FunctionCallingConfig.Mode.ANY,
+                  allowedFunctionNames = listOf("allowedFunctionName")
+                )
+              )
+          ),
         )
         .collect { channel.close() }
     }
 
     val requestBodyAsText = (mockEngine.requestHistory.first().body as TextContent).text
 
     requestBodyAsText shouldContainJsonKey "tool_config.function_calling_config.mode"
+    requestBodyAsText shouldContainJsonKey
+      "tool_config.function_calling_config.allowed_function_names"
   }
 
   @Test