Make NativeCmd step available in Gradle plugin

Maven support had been added in diffplug#949.

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

@@ -53,6 +53,7 @@
 import com.diffplug.spotless.generic.IndentStep;
 import com.diffplug.spotless.generic.LicenseHeaderStep;
 import com.diffplug.spotless.generic.LicenseHeaderStep.YearMode;
+import com.diffplug.spotless.generic.NativeCmdStep;
 import com.diffplug.spotless.generic.PipeStepPair;
 import com.diffplug.spotless.generic.ReplaceRegexStep;
 import com.diffplug.spotless.generic.ReplaceStep;
@@ -394,6 +395,11 @@ public void indentWithTabs() {
 		addStep(IndentStep.Type.TAB.create());
 	}
 
+	/** Ensures formatting of files via native binary. */
+	public void nativeCmd(String name, String pathToExe, List<String> arguments) {
+		addStep(NativeCmdStep.create(name, new File(pathToExe), arguments));
+	}
+
 	/**
 	 * Created by {@link FormatExtension#licenseHeader(String, String)} or {@link FormatExtension#licenseHeaderFile(Object, String)}.
 	 * For most language-specific formats (e.g. java, scala, etc.) you can omit the second {@code delimiter} argument, because it is supplied

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

@@ -0,0 +1,45 @@
+/*
+ * Copyright 2021 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 static org.assertj.core.api.Assumptions.assumeThat;
+
+import java.io.File;
+import java.io.IOException;
+
+import org.junit.jupiter.api.Test;
+
+class NativeCmdIntegrationTest extends GradleIntegrationHarness {
+	@Test
+	void nativeCmd() throws IOException {
+		// This will only work if /usr/bin/sed is available
+		assumeThat(new File("/usr/bin/sed")).exists();
+
+		setFile("build.gradle").toLines(
+				"plugins {",
+				"  id 'com.diffplug.spotless'",
+				"}",
+				"spotless {",
+				"  format 'test', {",
+				"    target '**/*.txt'",
+				"    nativeCmd('sed', '/usr/bin/sed', ['s/placeholder/replaced/g'])",
+				"  }",
+				"}");
+		setFile("test.txt").toResource("native_cmd/dirty.txt");
+		gradleRunner().withArguments("spotlessApply").build();
+		assertFile("test.txt").sameAsResource("native_cmd/clean.txt");
+	}
+}

testlib/src/main/resources/native_cmd/clean.txt

@@ -0,0 +1,2 @@
+replaced foo
+bar replaced

testlib/src/main/resources/native_cmd/dirty.txt

@@ -0,0 +1,2 @@
+placeholder foo
+bar placeholder