feat: replace prefab stage actions with headless modify_contents (#635)

Removes stage-based prefab editing (open_stage, close_stage, save_open_stage)
in favor of headless modify_contents action that uses PrefabUtility.LoadPrefabContents
for reliable automated workflows without UI dialogs.

Changes:
- Remove open_stage, close_stage, save_open_stage actions
- Add modify_contents action for headless prefab editing
- Support targeting objects by name or path (e.g., "Turret/Barrel")
- Support transform, tag, layer, setActive, name, parent, components operations
- Skip saving when no modifications made (avoids unnecessary asset writes)
- Delete PrefabStage.cs resource (no longer needed)
- Update Python tool description to remove "stages" reference
- Consolidate tests from 29 to 14 (covers complex prefabs, reparenting, hierarchy loop guard)

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
main
dsarno 2026-01-26 10:53:44 -08:00 committed by GitHub
parent f5ca9173b2
commit 17eb171e31
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5 changed files with 734 additions and 795 deletions

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@ -1,42 +0,0 @@
using System;
using MCPForUnity.Editor.Helpers;
using Newtonsoft.Json.Linq;
using UnityEditor.SceneManagement;
namespace MCPForUnity.Editor.Resources.Editor
{
/// <summary>
/// Provides information about the current prefab editing context.
/// </summary>
[McpForUnityResource("get_prefab_stage")]
public static class PrefabStage
{
public static object HandleCommand(JObject @params)
{
try
{
var stage = PrefabStageUtility.GetCurrentPrefabStage();
if (stage == null)
{
return new SuccessResponse("No prefab stage is currently open.", new { isOpen = false });
}
var stageInfo = new
{
isOpen = true,
assetPath = stage.assetPath,
prefabRootName = stage.prefabContentsRoot?.name,
mode = stage.mode.ToString(),
isDirty = stage.scene.isDirty
};
return new SuccessResponse("Prefab stage info retrieved.", stageInfo);
}
catch (Exception e)
{
return new ErrorResponse($"Error getting prefab stage info: {e.Message}");
}
}
}
}

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@ -1,11 +0,0 @@
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MonoImporter:
externalObjects: {}
serializedVersion: 2
defaultReferences: []
executionOrder: 0
icon: {instanceID: 0}
userData:
assetBundleName:
assetBundleVariant:

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@ -12,18 +12,17 @@ namespace MCPForUnity.Editor.Tools.Prefabs
{
[McpForUnityTool("manage_prefabs", AutoRegister = false)]
/// <summary>
/// Tool to manage Unity Prefab stages and create prefabs from GameObjects.
/// Tool to manage Unity Prefabs: create, inspect, and modify prefab assets.
/// Uses headless editing (no UI, no dialogs) for reliable automated workflows.
/// </summary>
public static class ManagePrefabs
{
// Action constants
private const string ACTION_OPEN_STAGE = "open_stage";
private const string ACTION_CLOSE_STAGE = "close_stage";
private const string ACTION_SAVE_OPEN_STAGE = "save_open_stage";
private const string ACTION_CREATE_FROM_GAMEOBJECT = "create_from_gameobject";
private const string ACTION_GET_INFO = "get_info";
private const string ACTION_GET_HIERARCHY = "get_hierarchy";
private const string SupportedActions = ACTION_OPEN_STAGE + ", " + ACTION_CLOSE_STAGE + ", " + ACTION_SAVE_OPEN_STAGE + ", " + ACTION_CREATE_FROM_GAMEOBJECT + ", " + ACTION_GET_INFO + ", " + ACTION_GET_HIERARCHY;
private const string ACTION_MODIFY_CONTENTS = "modify_contents";
private const string SupportedActions = ACTION_CREATE_FROM_GAMEOBJECT + ", " + ACTION_GET_INFO + ", " + ACTION_GET_HIERARCHY + ", " + ACTION_MODIFY_CONTENTS;
public static object HandleCommand(JObject @params)
{
@ -42,18 +41,14 @@ namespace MCPForUnity.Editor.Tools.Prefabs
{
switch (action)
{
case ACTION_OPEN_STAGE:
return OpenStage(@params);
case ACTION_CLOSE_STAGE:
return CloseStage(@params);
case ACTION_SAVE_OPEN_STAGE:
return SaveOpenStage(@params);
case ACTION_CREATE_FROM_GAMEOBJECT:
return CreatePrefabFromGameObject(@params);
case ACTION_GET_INFO:
return GetInfo(@params);
case ACTION_GET_HIERARCHY:
return GetHierarchy(@params);
case ACTION_MODIFY_CONTENTS:
return ModifyContents(@params);
default:
return new ErrorResponse($"Unknown action: '{action}'. Valid actions are: {SupportedActions}.");
}
@ -65,192 +60,6 @@ namespace MCPForUnity.Editor.Tools.Prefabs
}
}
/// <summary>
/// Opens a prefab in prefab mode for editing.
/// </summary>
private static object OpenStage(JObject @params)
{
string prefabPath = @params["prefabPath"]?.ToString();
if (string.IsNullOrEmpty(prefabPath))
{
return new ErrorResponse("'prefabPath' parameter is required for open_stage.");
}
string sanitizedPath = AssetPathUtility.SanitizeAssetPath(prefabPath);
if (string.IsNullOrEmpty(sanitizedPath))
{
return new ErrorResponse($"Invalid prefab path: '{prefabPath}'.");
}
GameObject prefabAsset = AssetDatabase.LoadAssetAtPath<GameObject>(sanitizedPath);
if (prefabAsset == null)
{
return new ErrorResponse($"No prefab asset found at path '{sanitizedPath}'.");
}
PrefabStage stage = PrefabStageUtility.OpenPrefab(sanitizedPath);
if (stage == null)
{
return new ErrorResponse($"Failed to open prefab stage for '{sanitizedPath}'.");
}
return new SuccessResponse($"Opened prefab stage for '{sanitizedPath}'.", SerializeStage(stage));
}
/// <summary>
/// Closes the currently open prefab stage, optionally saving first.
/// </summary>
private static object CloseStage(JObject @params)
{
PrefabStage stage = PrefabStageUtility.GetCurrentPrefabStage();
if (stage == null)
{
return new SuccessResponse("No prefab stage was open.");
}
string assetPath = stage.assetPath;
bool saveBeforeClose = @params["saveBeforeClose"]?.ToObject<bool>() ?? false;
if (saveBeforeClose && stage.scene.isDirty)
{
try
{
SaveAndRefreshStage(stage);
}
catch (Exception e)
{
return new ErrorResponse($"Failed to save prefab before closing: {e.Message}");
}
}
StageUtility.GoToMainStage();
return new SuccessResponse($"Closed prefab stage for '{assetPath}'.");
}
/// <summary>
/// Saves changes to the currently open prefab stage.
/// Supports a 'force' parameter for automated workflows where isDirty may not be set.
/// </summary>
private static object SaveOpenStage(JObject @params)
{
PrefabStage stage = PrefabStageUtility.GetCurrentPrefabStage();
if (stage == null)
{
return new ErrorResponse("No prefab stage is currently open.");
}
if (!ValidatePrefabStageForSave(stage))
{
return new ErrorResponse("Prefab stage validation failed. Cannot save.");
}
// Check for force parameter (useful for automated workflows)
bool force = @params?["force"]?.ToObject<bool>() ?? false;
// Check if there are actual changes to save
bool wasDirty = stage.scene.isDirty;
if (!wasDirty && !force)
{
return new SuccessResponse($"Prefab stage for '{stage.assetPath}' has no unsaved changes.", SerializeStage(stage));
}
try
{
SaveAndRefreshStage(stage, force);
return new SuccessResponse($"Saved prefab stage for '{stage.assetPath}'.", SerializeStage(stage));
}
catch (Exception e)
{
return new ErrorResponse($"Failed to save prefab: {e.Message}");
}
}
#region Prefab Save Operations
/// <summary>
/// Saves the prefab stage and refreshes the asset database.
/// Uses PrefabUtility.SaveAsPrefabAsset for reliable prefab saving without dialogs.
/// </summary>
/// <param name="stage">The prefab stage to save.</param>
/// <param name="force">If true, marks the prefab dirty before saving to ensure changes are captured.</param>
private static void SaveAndRefreshStage(PrefabStage stage, bool force = false)
{
if (stage == null)
{
throw new ArgumentNullException(nameof(stage), "Prefab stage cannot be null.");
}
if (stage.prefabContentsRoot == null)
{
throw new InvalidOperationException("Cannot save prefab stage without a prefab root.");
}
if (string.IsNullOrEmpty(stage.assetPath))
{
throw new InvalidOperationException("Prefab stage has invalid asset path.");
}
// When force=true, mark the prefab root dirty to ensure changes are saved
// This is useful for automated workflows where isDirty may not be set correctly
if (force)
{
EditorUtility.SetDirty(stage.prefabContentsRoot);
EditorSceneManager.MarkSceneDirty(stage.scene);
}
// Mark all children as dirty to ensure their changes are captured
foreach (Transform child in stage.prefabContentsRoot.GetComponentsInChildren<Transform>(true))
{
if (child != stage.prefabContentsRoot.transform)
{
EditorUtility.SetDirty(child.gameObject);
}
}
// Use PrefabUtility.SaveAsPrefabAsset which saves without dialogs
// This is more reliable for automated workflows than EditorSceneManager.SaveScene
bool success;
PrefabUtility.SaveAsPrefabAsset(stage.prefabContentsRoot, stage.assetPath, out success);
if (!success)
{
throw new InvalidOperationException($"Failed to save prefab asset for '{stage.assetPath}'.");
}
// Ensure changes are persisted to disk
AssetDatabase.SaveAssets();
AssetDatabase.Refresh();
McpLog.Info($"[ManagePrefabs] Successfully saved prefab '{stage.assetPath}'.");
}
/// <summary>
/// Validates prefab stage before saving.
/// </summary>
private static bool ValidatePrefabStageForSave(PrefabStage stage)
{
if (stage == null)
{
McpLog.Warn("[ManagePrefabs] No prefab stage is open.");
return false;
}
if (stage.prefabContentsRoot == null)
{
McpLog.Error($"[ManagePrefabs] Prefab stage '{stage.assetPath}' has no root object.");
return false;
}
if (string.IsNullOrEmpty(stage.assetPath))
{
McpLog.Error("[ManagePrefabs] Prefab stage has invalid asset path.");
return false;
}
return true;
}
#endregion
#region Create Prefab from GameObject
/// <summary>
@ -618,6 +427,307 @@ namespace MCPForUnity.Editor.Tools.Prefabs
#endregion
#region Headless Prefab Editing
/// <summary>
/// Modifies a prefab's contents directly without opening the prefab stage.
/// This is ideal for automated/agentic workflows as it avoids UI, dirty flags, and dialogs.
/// </summary>
private static object ModifyContents(JObject @params)
{
string prefabPath = @params["prefabPath"]?.ToString() ?? @params["path"]?.ToString();
if (string.IsNullOrEmpty(prefabPath))
{
return new ErrorResponse("'prefabPath' parameter is required for modify_contents.");
}
string sanitizedPath = AssetPathUtility.SanitizeAssetPath(prefabPath);
if (string.IsNullOrEmpty(sanitizedPath))
{
return new ErrorResponse($"Invalid prefab path '{prefabPath}'. Path traversal sequences are not allowed.");
}
// Load prefab contents in isolated context (no UI)
GameObject prefabContents = PrefabUtility.LoadPrefabContents(sanitizedPath);
if (prefabContents == null)
{
return new ErrorResponse($"Failed to load prefab contents from '{sanitizedPath}'.");
}
try
{
// Find target object within the prefab (defaults to root)
string targetName = @params["target"]?.ToString();
GameObject targetGo = FindInPrefabContents(prefabContents, targetName);
if (targetGo == null)
{
string searchedFor = string.IsNullOrEmpty(targetName) ? "root" : $"'{targetName}'";
return new ErrorResponse($"Target {searchedFor} not found in prefab '{sanitizedPath}'.");
}
// Apply modifications
var modifyResult = ApplyModificationsToPrefabObject(targetGo, @params, prefabContents);
if (modifyResult.error != null)
{
return modifyResult.error;
}
// Skip saving when no modifications were made to avoid unnecessary asset writes
if (!modifyResult.modified)
{
return new SuccessResponse(
$"Prefab '{sanitizedPath}' is already up to date; no changes were applied.",
new
{
prefabPath = sanitizedPath,
targetName = targetGo.name,
modified = false
}
);
}
// Save the prefab
bool success;
PrefabUtility.SaveAsPrefabAsset(prefabContents, sanitizedPath, out success);
if (!success)
{
return new ErrorResponse($"Failed to save prefab asset at '{sanitizedPath}'.");
}
AssetDatabase.Refresh();
McpLog.Info($"[ManagePrefabs] Successfully modified and saved prefab '{sanitizedPath}' (headless).");
return new SuccessResponse(
$"Prefab '{sanitizedPath}' modified and saved successfully.",
new
{
prefabPath = sanitizedPath,
targetName = targetGo.name,
modified = modifyResult.modified,
transform = new
{
position = new { x = targetGo.transform.localPosition.x, y = targetGo.transform.localPosition.y, z = targetGo.transform.localPosition.z },
rotation = new { x = targetGo.transform.localEulerAngles.x, y = targetGo.transform.localEulerAngles.y, z = targetGo.transform.localEulerAngles.z },
scale = new { x = targetGo.transform.localScale.x, y = targetGo.transform.localScale.y, z = targetGo.transform.localScale.z }
},
componentTypes = PrefabUtilityHelper.GetComponentTypeNames(targetGo)
}
);
}
finally
{
// Always unload prefab contents to free memory
PrefabUtility.UnloadPrefabContents(prefabContents);
}
}
/// <summary>
/// Finds a GameObject within loaded prefab contents by name or path.
/// </summary>
private static GameObject FindInPrefabContents(GameObject prefabContents, string target)
{
if (string.IsNullOrEmpty(target))
{
// Return root if no target specified
return prefabContents;
}
// Try to find by path first (e.g., "Parent/Child/Target")
if (target.Contains("/"))
{
Transform found = prefabContents.transform.Find(target);
if (found != null)
{
return found.gameObject;
}
// If path starts with root name, try without it
if (target.StartsWith(prefabContents.name + "/"))
{
string relativePath = target.Substring(prefabContents.name.Length + 1);
found = prefabContents.transform.Find(relativePath);
if (found != null)
{
return found.gameObject;
}
}
}
// Check if target matches root name
if (prefabContents.name == target)
{
return prefabContents;
}
// Search by name in hierarchy
foreach (Transform t in prefabContents.GetComponentsInChildren<Transform>(true))
{
if (t.gameObject.name == target)
{
return t.gameObject;
}
}
return null;
}
/// <summary>
/// Applies modifications to a GameObject within loaded prefab contents.
/// Returns (modified: bool, error: ErrorResponse or null).
/// </summary>
private static (bool modified, ErrorResponse error) ApplyModificationsToPrefabObject(GameObject targetGo, JObject @params, GameObject prefabRoot)
{
bool modified = false;
// Name change
string newName = @params["name"]?.ToString();
if (!string.IsNullOrEmpty(newName) && targetGo.name != newName)
{
// If renaming the root, this will affect the prefab asset name on save
targetGo.name = newName;
modified = true;
}
// Active state
bool? setActive = @params["setActive"]?.ToObject<bool?>();
if (setActive.HasValue && targetGo.activeSelf != setActive.Value)
{
targetGo.SetActive(setActive.Value);
modified = true;
}
// Tag
string tag = @params["tag"]?.ToString();
if (tag != null && targetGo.tag != tag)
{
string tagToSet = string.IsNullOrEmpty(tag) ? "Untagged" : tag;
try
{
targetGo.tag = tagToSet;
modified = true;
}
catch (Exception ex)
{
return (false, new ErrorResponse($"Failed to set tag to '{tagToSet}': {ex.Message}"));
}
}
// Layer
string layerName = @params["layer"]?.ToString();
if (!string.IsNullOrEmpty(layerName))
{
int layerId = LayerMask.NameToLayer(layerName);
if (layerId == -1)
{
return (false, new ErrorResponse($"Invalid layer specified: '{layerName}'. Use a valid layer name."));
}
if (targetGo.layer != layerId)
{
targetGo.layer = layerId;
modified = true;
}
}
// Transform: position, rotation, scale
Vector3? position = VectorParsing.ParseVector3(@params["position"]);
Vector3? rotation = VectorParsing.ParseVector3(@params["rotation"]);
Vector3? scale = VectorParsing.ParseVector3(@params["scale"]);
if (position.HasValue && targetGo.transform.localPosition != position.Value)
{
targetGo.transform.localPosition = position.Value;
modified = true;
}
if (rotation.HasValue && targetGo.transform.localEulerAngles != rotation.Value)
{
targetGo.transform.localEulerAngles = rotation.Value;
modified = true;
}
if (scale.HasValue && targetGo.transform.localScale != scale.Value)
{
targetGo.transform.localScale = scale.Value;
modified = true;
}
// Parent change (within prefab hierarchy)
JToken parentToken = @params["parent"];
if (parentToken != null)
{
string parentTarget = parentToken.ToString();
Transform newParent = null;
if (!string.IsNullOrEmpty(parentTarget))
{
GameObject parentGo = FindInPrefabContents(prefabRoot, parentTarget);
if (parentGo == null)
{
return (false, new ErrorResponse($"Parent '{parentTarget}' not found in prefab."));
}
if (parentGo.transform.IsChildOf(targetGo.transform))
{
return (false, new ErrorResponse($"Cannot parent '{targetGo.name}' to '{parentGo.name}' as it would create a hierarchy loop."));
}
newParent = parentGo.transform;
}
if (targetGo.transform.parent != newParent)
{
targetGo.transform.SetParent(newParent, true);
modified = true;
}
}
// Components to add
if (@params["componentsToAdd"] is JArray componentsToAdd)
{
foreach (var compToken in componentsToAdd)
{
string typeName = compToken.Type == JTokenType.String
? compToken.ToString()
: (compToken as JObject)?["typeName"]?.ToString();
if (!string.IsNullOrEmpty(typeName))
{
if (!ComponentResolver.TryResolve(typeName, out Type componentType, out string error))
{
return (false, new ErrorResponse($"Component type '{typeName}' not found: {error}"));
}
targetGo.AddComponent(componentType);
modified = true;
}
}
}
// Components to remove
if (@params["componentsToRemove"] is JArray componentsToRemove)
{
foreach (var compToken in componentsToRemove)
{
string typeName = compToken.ToString();
if (!string.IsNullOrEmpty(typeName))
{
if (!ComponentResolver.TryResolve(typeName, out Type componentType, out string error))
{
return (false, new ErrorResponse($"Component type '{typeName}' not found: {error}"));
}
Component comp = targetGo.GetComponent(componentType);
if (comp != null)
{
UnityEngine.Object.DestroyImmediate(comp);
modified = true;
}
}
}
}
return (modified, null);
}
#endregion
#region Hierarchy Builder
/// <summary>
@ -689,25 +799,5 @@ namespace MCPForUnity.Editor.Tools.Prefabs
}
#endregion
/// <summary>
/// Serializes the prefab stage information for response.
/// </summary>
private static object SerializeStage(PrefabStage stage)
{
if (stage == null)
{
return new { isOpen = false };
}
return new
{
isOpen = true,
assetPath = stage.assetPath,
prefabRootName = stage.prefabContentsRoot != null ? stage.prefabContentsRoot.name : null,
mode = stage.mode.ToString(),
isDirty = stage.scene.isDirty
};
}
}
}

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@ -15,17 +15,16 @@ from services.tools.preflight import preflight
REQUIRED_PARAMS = {
"get_info": ["prefab_path"],
"get_hierarchy": ["prefab_path"],
"open_stage": ["prefab_path"],
"create_from_gameobject": ["target", "prefab_path"],
"save_open_stage": [],
"close_stage": [],
"modify_contents": ["prefab_path"],
}
@mcp_for_unity_tool(
description=(
"Manages Unity Prefab assets and stages. "
"Actions: get_info, get_hierarchy, open_stage, close_stage, save_open_stage, create_from_gameobject. "
"Manages Unity Prefab assets via headless operations (no UI, no prefab stages). "
"Actions: get_info, get_hierarchy, create_from_gameobject, modify_contents. "
"Use modify_contents for headless prefab editing - ideal for automated workflows. "
"Use manage_asset action=search filterType=Prefab to list prefabs."
),
annotations=ToolAnnotations(
@ -37,27 +36,39 @@ async def manage_prefabs(
ctx: Context,
action: Annotated[
Literal[
"open_stage",
"close_stage",
"save_open_stage",
"create_from_gameobject",
"get_info",
"get_hierarchy",
"modify_contents",
],
"Prefab operation to perform.",
],
prefab_path: Annotated[str, "Prefab asset path (e.g., Assets/Prefabs/MyPrefab.prefab)."] | None = None,
save_before_close: Annotated[bool, "Save before closing if unsaved changes exist."] | None = None,
target: Annotated[str, "Scene GameObject name for create_from_gameobject."] | None = None,
target: Annotated[str, "Target GameObject: scene object for create_from_gameobject, or object within prefab for modify_contents (name or path like 'Parent/Child')."] | None = None,
allow_overwrite: Annotated[bool, "Allow replacing existing prefab."] | None = None,
search_inactive: Annotated[bool, "Include inactive GameObjects in search."] | None = None,
unlink_if_instance: Annotated[bool, "Unlink from existing prefab before creating new one."] | None = None,
force: Annotated[bool, "Force save even if no changes detected. Useful for automated workflows."] | None = None,
# modify_contents parameters
position: Annotated[list[float], "New local position [x, y, z] for modify_contents."] | None = None,
rotation: Annotated[list[float], "New local rotation (euler angles) [x, y, z] for modify_contents."] | None = None,
scale: Annotated[list[float], "New local scale [x, y, z] for modify_contents."] | None = None,
name: Annotated[str, "New name for the target object in modify_contents."] | None = None,
tag: Annotated[str, "New tag for the target object in modify_contents."] | None = None,
layer: Annotated[str, "New layer name for the target object in modify_contents."] | None = None,
set_active: Annotated[bool, "Set active state of target object in modify_contents."] | None = None,
parent: Annotated[str, "New parent object name/path within prefab for modify_contents."] | None = None,
components_to_add: Annotated[list[str], "Component types to add in modify_contents."] | None = None,
components_to_remove: Annotated[list[str], "Component types to remove in modify_contents."] | None = None,
) -> dict[str, Any]:
# Back-compat: map 'name' → 'target' for create_from_gameobject (Unity accepts both)
if action == "create_from_gameobject" and target is None and name is not None:
target = name
# Validate required parameters
required = REQUIRED_PARAMS.get(action, [])
for param_name in required:
param_value = locals().get(param_name)
# Use updated local value for target after back-compat mapping
param_value = target if param_name == "target" else locals().get(param_name)
# Check for None and empty/whitespace strings
if param_value is None or (isinstance(param_value, str) and not param_value.strip()):
return {
@ -86,11 +97,6 @@ async def manage_prefabs(
if prefab_path:
params["prefabPath"] = prefab_path
# Handle boolean parameters with proper coercion
save_before_close_val = coerce_bool(save_before_close)
if save_before_close_val is not None:
params["saveBeforeClose"] = save_before_close_val
if target:
params["target"] = target
@ -106,9 +112,28 @@ async def manage_prefabs(
if unlink_if_instance_val is not None:
params["unlinkIfInstance"] = unlink_if_instance_val
force_val = coerce_bool(force)
if force_val is not None:
params["force"] = force_val
# modify_contents parameters
if position is not None:
params["position"] = position
if rotation is not None:
params["rotation"] = rotation
if scale is not None:
params["scale"] = scale
if name is not None:
params["name"] = name
if tag is not None:
params["tag"] = tag
if layer is not None:
params["layer"] = layer
set_active_val = coerce_bool(set_active)
if set_active_val is not None:
params["setActive"] = set_active_val
if parent is not None:
params["parent"] = parent
if components_to_add is not None:
params["componentsToAdd"] = components_to_add
if components_to_remove is not None:
params["componentsToRemove"] = components_to_remove
# Send command to Unity
response = await send_with_unity_instance(