pb_SaveMesh.cs

using UnityEngine;
using UnityEditor;

public static class pb_SaveMesh
{
	[MenuItem("Tools/" + pb_Constant.PRODUCT_NAME + "/Object/Save Mesh", validate = true)]
	private static bool VALIDATE_SaveSelectedMesh()
	{
		if(Selection.activeGameObject != null)
		{
			pb_Object obj = Selection.activeGameObject.GetComponent<pb_Object>();
			return obj != null;
		}

		return false;
	}

	[MenuItem("Tools/" + pb_Constant.PRODUCT_NAME + "/Object/Save Object")]
	private static void SaveSelectedMesh()
	{
		string savePath = EditorUtility.SaveFilePanelInProject("Save ProBuilder Mesh", Selection.activeGameObject.name, "prefab", "");
		if(string.IsNullOrEmpty(savePath))
			return;

		GameObject gameObject = GameObject.Instantiate(Selection.activeGameObject, Selection.activeGameObject.transform.position, Selection.activeGameObject.transform.rotation) as GameObject;
		MeshFilter meshFilter = gameObject.GetComponent<MeshFilter>();
		Mesh mesh = Mesh.Instantiate<Mesh>(meshFilter.sharedMesh);
		mesh.hideFlags = HideFlags.None;
		mesh.name = meshFilter.sharedMesh.name;

		RemoveComponent<pb_Object>(gameObject);
		RemoveComponent<pb_Entity>(gameObject);
		
		GameObject prefab = PrefabUtility.CreatePrefab(savePath, gameObject, ReplacePrefabOptions.Default);
		MeshFilter prefabMeshFilter = prefab.GetComponent<MeshFilter>();
		MeshCollider prefabMeshCollider = prefab.GetComponent<MeshCollider>();

		AssetDatabase.AddObjectToAsset(mesh, prefab);
		prefabMeshFilter.sharedMesh = mesh;
		prefabMeshCollider.sharedMesh = mesh;
		
		GameObject.DestroyImmediate(gameObject);
		AssetDatabase.ImportAsset(AssetDatabase.GetAssetPath(prefab));

		Selection.activeGameObject = prefab;
		ProjectWindowUtil.ShowCreatedAsset(prefab);
	}

	private static void RemoveComponent<T>(GameObject gameObject) where T : Component
	{
		T comp = gameObject.GetComponent<T>();
		if(comp != null)
		{
			Component.DestroyImmediate(comp);
		}
	}
}