BuildOnlyDefine.cs

using UnityEngine;
using UnityEditor.Callbacks;
using UnityEditor.Build;
using UnityEditor;
using UnityEditor.Build.Reporting;

public class BuildOnlyDefine : IPreprocessBuildWithReport, IPostprocessBuildWithReport
{
	int IOrderedCallback.callbackOrder => 1;

	public static string runtimeOnlyDefines = "UNITY_RUNTIME"; // example of multiple defines: "UNITY_RUNTIME;UNITY_NOT_EDITOR"

	static BuildTargetGroup currentTarget
	{
		get
		{
#if UNITY_STANDALONE
			return BuildTargetGroup.Standalone;
#elif UNITY_ANDROID
			return BuildTargetGroup.Android;
#elif UNITY_IOS
			return BuildTargetGroup.iOS;
#endif
		}
	}

	// CALLED BEFORE THE BUILD
	public void OnPreprocessBuild(BuildReport report)
	{
		Debug.Log("BuildOnlyDefine: before build: adding symbols: " + runtimeOnlyDefines);

		// Start listening for errors when build starts
		Application.logMessageReceived += OnBuildError;

		string str = PlayerSettings.GetScriptingDefineSymbolsForGroup(currentTarget);
		PlayerSettings.SetScriptingDefineSymbolsForGroup(currentTarget, str + ";" + runtimeOnlyDefines);
		AssetDatabase.Refresh();
	}

	// CALLED DURING BUILD TO CHECK FOR ERRORS
	private void OnBuildError(string condition, string stacktrace, LogType type)
	{
		if (type == LogType.Error || type == LogType.Exception || type == LogType.Assert)
		{
			Debug.Log("BuildOnlyDefine: Error message received during build process");
			// FAILED TO BUILD, CALL POSTPROCESS ANYWAY
			OnPostprocessBuild(null);
		}
	}

	// CALLED AFTER THE BUILD
	public void OnPostprocessBuild(BuildReport report)
	{
		Debug.Log("BuildOnlyDefine: after build: removing symbols: " + runtimeOnlyDefines);

		// IF BUILD FINISHED AND SUCCEEDED, STOP LOOKING FOR ERRORS
		Application.logMessageReceived -= OnBuildError;

		string str = PlayerSettings.GetScriptingDefineSymbolsForGroup(currentTarget);
		PlayerSettings.SetScriptingDefineSymbolsForGroup(currentTarget, str.Replace(runtimeOnlyDefines, ""));
		AssetDatabase.Refresh();
	}
}