Editor class that will automatically set the scriptExecutionOrder based on using a ScriptExecutionAttribute.

ScriptExecutionAssignment.cs

// ScriptExecutionAssignment
// NoiseCrime
// 11.10.2016
// 05.06.2016
//
//
// Editor class that will automatically set the scriptExecutionOrder based on using a ScriptExecutionAttribute.
// See ScriptExecutionAttribute.cs Gist!
// The class is called automatically everytime Unity recompiles the project - see [InitializeOnLoad]
//
// This script MUST be placed into an Editor Folder in your Unity Project.
// Requires Script names to match class name.
// Likely only works with a single class defined per file.
// Unfortunately the script will also execute everytime you run the project in the editor ( play ), so use defines below to control behaviour.
// 
// ENABLE_SCRIPT:		If NOT defined the script will not run.
// ENABLE_ASSIGNMENT:	If NOT defined this will prevent execution of the script.
// ENABLE_LOGGING: 		If defined will log ( sorted by order ) to the console all found classes using the ScriptExecutionAttribute and their script order.
// ENABLE_MONO_LOGGING: If defined will log all scripts in mono that are not using default ScriptExecution value.

// #define ENABLE_SCRIPT
#define ENABLE_LOGGING
#define ENABLE_MONO_LOGGING
#define ENABLE_ASSIGNMENT


using UnityEngine;
using UnityEditor;

using System;
using System.Linq;
using System.Collections.Generic;

[InitializeOnLoad]
public class ScriptExecutionAssignment : Editor
{

	static ScriptExecutionAssignment()
	{
#if ENABLE_SCRIPT
		if( EditorApplication.isCompiling || EditorApplication.isPaused || EditorApplication.isPlaying) return;
		
	#if ENABLE_MONO_LOGGING 
		LogAllMonoScripts();
	#endif   

		AssignExecutionOrderToMonoScripts();
#else
		Debug.LogWarning("EDITOR: ScriptExecutionAssignment is disabled - check script define.");
#endif
	}
	

	static void LogAllMonoScripts()
	{
		Dictionary<string, int[]> executionOrderLogging = new Dictionary<string, int[]>();

		// Lock Assemblies
		EditorApplication.LockReloadAssemblies();
		
		foreach (MonoScript monoScript in MonoImporter.GetAllRuntimeMonoScripts())
		{			
			Type monoClass = monoScript.GetClass();

			if( monoClass != null)
			{				
				int executionOrderOriginal = MonoImporter.GetExecutionOrder(monoScript);
				if(executionOrderOriginal != 0) executionOrderLogging.Add( monoScript.name, new int[ 2 ] { executionOrderOriginal, executionOrderOriginal } );
			}
		}

		// Unlock Assemblies
		EditorApplication.UnlockReloadAssemblies();
		
		LogResults("GetExecutionOrder", executionOrderLogging);
	}


	static void AssignExecutionOrderToMonoScripts()
	{
#if ENABLE_LOGGING
		Dictionary<string, int[]> executionOrderLogging = new Dictionary<string, int[]>();
#endif

		// Lock Assemblies
		EditorApplication.LockReloadAssemblies();
		
		foreach (MonoScript monoScript in MonoImporter.GetAllRuntimeMonoScripts())
		{			
			Type monoClass = monoScript.GetClass();

			if( monoClass != null)
			{
				Attribute att = Attribute.GetCustomAttribute(monoClass, typeof(ScriptExecutionAttribute));

				if( att != null)
				{
					int executionOrderTarget   = ((ScriptExecutionAttribute)att).executionIndex;
					int executionOrderOriginal = MonoImporter.GetExecutionOrder(monoScript);

					#if ENABLE_LOGGING
					executionOrderLogging.Add( monoScript.name, new int[ 2 ] { executionOrderOriginal, executionOrderTarget } );
					#endif

					#if ENABLE_ASSIGNMENT
					// It is important not to set the execution order if the value is already correct!
					if (executionOrderOriginal != executionOrderTarget)
					{
						MonoImporter.SetExecutionOrder(monoScript, executionOrderTarget);

						#if ENABLE_LOGGING
						Debug.LogWarning(Decorate.Warning("The script " + monoScript.name + " was not set to correct Script Execution Order - it has been fixed and set to " + executionOrderTarget + " from " + executionOrderOriginal));
						#endif
					}
					#endif   
				}
			}
		}

		// Unlock Assemblies
		EditorApplication.UnlockReloadAssemblies();

#if ENABLE_LOGGING	
		LogResults("ScriptExecutionAttribute", executionOrderLogging);
#endif
	}



	// Simple logging to console with the dictionary of found classes sorted by execution order.
	static void LogResults( string title, Dictionary<string, int[]> results )
	{	
		if ( results.Count > 0 )
		{
			string logging = title + ": Found Types\n";

			foreach ( KeyValuePair<string, int[]> item in results.OrderBy( key => key.Value[ 1 ] ) )
				logging += string.Format( "<color={0}>ScriptExecutionAttribute: Current: {0}  Target: {1}  Type: {2}</color>\n", item.Value[ 0 ], item.Value[ 1 ], item.Key, ( item.Value[ 0 ] == item.Value[ 1 ] ? "#F0F0F0" : "#FF0000" ) );

			Debug.Log( logging );
		}
	}	
}