Yup, custom still needs Gradle 8.0+, bring that back.

Author: nedtwigg

plugin-gradle/src/main/java/com/diffplug/gradle/spotless/FormatExtension.java

@@ -16,6 +16,8 @@
 package com.diffplug.gradle.spotless;
 
 import static com.diffplug.gradle.spotless.PluginGradlePreconditions.requireElementsNonNull;
+import static com.diffplug.gradle.spotless.SpotlessPluginRedirect.badSemver;
+import static com.diffplug.gradle.spotless.SpotlessPluginRedirect.badSemverOfGradle;
 import static java.util.Objects.requireNonNull;
 
 import java.io.File;
@@ -44,6 +46,7 @@
 import org.gradle.api.file.FileCollection;
 import org.gradle.api.plugins.BasePlugin;
 import org.gradle.api.tasks.TaskProvider;
+import org.gradle.util.GradleVersion;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -484,6 +487,12 @@ private void readObject(java.io.ObjectInputStream stream) throws java.io.IOExcep
 	 */
 	public void custom(String name, FormatterFunc formatter) {
 		requireNonNull(formatter, "formatter");
+		if (badSemverOfGradle() < badSemver(SpotlessPlugin.VER_GRADLE_minVersionForCustom)) {
+			throw new GradleException("The 'custom' method is only available if you are using Gradle "
+					+ SpotlessPlugin.VER_GRADLE_minVersionForCustom
+					+ " or newer, this is "
+					+ GradleVersion.current().getVersion());
+		}
 		addStep(FormatterStep.createLazy(name, () -> globalState, SerializedFunction.alwaysReturns(formatter)));
 	}
 

plugin-gradle/src/test/java/com/diffplug/gradle/spotless/BumpThisNumberIfACustomStepChangesTest.java

@@ -44,7 +44,7 @@ public GradleRunner gradleRunner() throws IOException {
 		if (useConfigCache) {
 			setFile("gradle.properties").toLines("org.gradle.unsafe.configuration-cache=true",
 					"org.gradle.configuration-cache=true");
-			return super.gradleRunner().withGradleVersion(GradleVersionSupport.CONFIGURATION_CACHE.version);
+			return super.gradleRunner().withGradleVersion(GradleVersionSupport.CUSTOM_STEPS.version);
 		} else {
 			return super.gradleRunner();
 		}