Restore GradleCompat with IP safe approach

Author: inorichi

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

@@ -635,8 +635,7 @@ public LicenseHeaderConfig updateYearWithLatest(boolean updateYearWithLatest) {
 
 		FormatterStep createStep() {
 			return builder.withYearModeLazy(() -> {
-				String yearProperty = spotless.project.getProviders().gradleProperty(LicenseHeaderStep.FLAG_SET_LICENSE_HEADER_YEARS_FROM_GIT_HISTORY()).getOrNull();
-				if (Boolean.parseBoolean(yearProperty)) {
+				if (Boolean.parseBoolean(GradleCompat.findOptionalProperty(spotless.project, LicenseHeaderStep.FLAG_SET_LICENSE_HEADER_YEARS_FROM_GIT_HISTORY()))) {
 					return YearMode.SET_FROM_GIT;
 				} else {
 					boolean updateYear = updateYearWithLatest == null ? getRatchetFrom() != null : updateYearWithLatest;

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

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2025-2026 DiffPlug
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.diffplug.gradle.spotless;
+
+import javax.annotation.Nullable;
+
+import org.gradle.api.Project;
+import org.gradle.api.plugins.ExtraPropertiesExtension;
+
+public final class GradleCompat {
+	private GradleCompat() {}
+
+	@Nullable public static String findOptionalProperty(Project project, String propertyName) {
+		@Nullable String value = project.getProviders().gradleProperty(propertyName).getOrNull();
+		if (value != null) {
+			return value;
+		}
+		ExtraPropertiesExtension extras = project.getExtensions().getByType(ExtraPropertiesExtension.class);
+		if (extras.has(propertyName)) {
+			@Nullable Object property = extras.get(propertyName);
+			if (property != null) {
+				return property.toString();
+			}
+		}
+		return null;
+	}
+
+	public static boolean isPropertyPresent(Project project, String propertyName) {
+		return project.getProviders().gradleProperty(propertyName).isPresent() ||
+				project.getExtensions().getByType(ExtraPropertiesExtension.class).has(propertyName);
+	}
+}

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

@@ -39,10 +39,10 @@ static class State extends NoLambda.EqualityBasedOnSerialization {
 		final boolean useStdOut;
 
 		State(Project project) {
-			var pathsString = project.getProviders().gradleProperty(PROPERTY).getOrNull();
+			var pathsString = GradleCompat.findOptionalProperty(project, PROPERTY);
 			if (pathsString != null) {
-				useStdIn = project.getProviders().gradleProperty(USE_STD_IN).isPresent();
-				useStdOut = project.getProviders().gradleProperty(USE_STD_OUT).isPresent();
+				useStdIn = GradleCompat.isPropertyPresent(project, USE_STD_IN);
+				useStdOut = GradleCompat.isPropertyPresent(project, USE_STD_OUT);
 				paths = Arrays.stream(pathsString.split(","))
 						.map(String::trim)
 						.filter(s -> !s.isEmpty())

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2026 DiffPlug
+ * Copyright 2016-2025 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -42,7 +42,7 @@ public void apply(Project project) {
 					+ "https://docs.gradle.org/current/userguide/building_java_projects.html#sec:java_cross_compilation");
 		}
 		// if -PspotlessModern=true, then use the modern stuff instead of the legacy stuff
-		if (project.getProviders().gradleProperty(SPOTLESS_MODERN).isPresent()) {
+		if (GradleCompat.isPropertyPresent(project, SPOTLESS_MODERN)) {
 			project.getLogger().warn("'spotlessModern' has no effect as of Spotless 5.0, recommend removing it.");
 		}
 		// make sure there's a `clean` and a `check`