fix: separate node_modules dir per npm based formatter

without this change, using the exact same npm-based formatter (e.g.
prettier) in multiple formatters, we could end up using the same
directory to store their node_modules inside. This could lead -
especially when using parallel builds, to a lot of issues:
- overwriting each others node_modules mid-flight
- overwriting package.json mid-flight
- starting multiple npm-based servers on the same directory (overwriting
the port-file thus leading to cross-access between formatter steps and
their corresponding node server).

By applying this fix, each formatter will have its own separate
node_modules directory.

lib/src/main/java/com/diffplug/spotless/npm/EslintFormatterStep.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2024 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.
@@ -68,13 +68,14 @@ public static Map<String, String> defaultDevDependenciesWithEslint(String versio
 		return Collections.singletonMap("eslint", version);
 	}
 
-	public static FormatterStep create(Map<String, String> devDependencies, Provisioner provisioner, File projectDir, File buildDir, File cacheDir, NpmPathResolver npmPathResolver, EslintConfig eslintConfig) {
+	public static FormatterStep create(String formatName, Map<String, String> devDependencies, Provisioner provisioner, File projectDir, File buildDir, File cacheDir, NpmPathResolver npmPathResolver, EslintConfig eslintConfig) {
 		requireNonNull(devDependencies);
 		requireNonNull(provisioner);
 		requireNonNull(projectDir);
 		requireNonNull(buildDir);
-		return FormatterStep.createLazy(NAME,
-				() -> new State(NAME, devDependencies, projectDir, buildDir, cacheDir, npmPathResolver, eslintConfig),
+		final String prefixedName = String.format("%s-%s", formatName, NAME);
+		return FormatterStep.createLazy(prefixedName,
+				() -> new State(prefixedName, devDependencies, projectDir, buildDir, cacheDir, npmPathResolver, eslintConfig),
 				State::createFormatterFunc);
 	}
 

lib/src/main/java/com/diffplug/spotless/npm/NpmFormatterStepStateBase.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2024 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.
@@ -69,7 +69,7 @@ public static class Runtime {
 
 		Runtime(NpmFormatterStepStateBase parent) {
 			this.parent = parent;
-			this.nodeServerLayout = new NodeServerLayout(parent.locations.buildDir(), parent.npmConfig.getPackageJsonContent());
+			this.nodeServerLayout = new NodeServerLayout(new File(parent.locations.buildDir(), parent.stepName), parent.npmConfig.getPackageJsonContent());
 			this.nodeServeApp = new NodeServeApp(nodeServerLayout, parent.npmConfig, parent.locations);
 		}
 

lib/src/main/java/com/diffplug/spotless/npm/PrettierFormatterStep.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2024 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.
@@ -51,12 +51,13 @@ public static final Map<String, String> defaultDevDependenciesWithPrettier(Strin
 		return Collections.singletonMap("prettier", version);
 	}
 
-	public static FormatterStep create(Map<String, String> devDependencies, Provisioner provisioner, File projectDir, File buildDir, File cacheDir, NpmPathResolver npmPathResolver, PrettierConfig prettierConfig) {
+	public static FormatterStep create(String formatName, Map<String, String> devDependencies, Provisioner provisioner, File projectDir, File buildDir, File cacheDir, NpmPathResolver npmPathResolver, PrettierConfig prettierConfig) {
 		requireNonNull(devDependencies);
 		requireNonNull(provisioner);
 		requireNonNull(buildDir);
-		return FormatterStep.createLazy(NAME,
-				() -> new State(NAME, devDependencies, projectDir, buildDir, cacheDir, npmPathResolver, prettierConfig),
+		final String prefixedName = String.format("%s-%s", formatName, NAME);
+		return FormatterStep.createLazy(prefixedName,
+				() -> new State(prefixedName, devDependencies, projectDir, buildDir, cacheDir, npmPathResolver, prettierConfig),
 				State::createFormatterFunc);
 	}
 

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

@@ -798,7 +798,7 @@ public PrettierConfig config(final Map<String, Object> prettierConfig) {
 		@Override
 		protected FormatterStep createStep() {
 			final Project project = getProject();
-			return PrettierFormatterStep.create(devDependencies, provisioner(), project.getProjectDir(),
+			return PrettierFormatterStep.create(formatName(), devDependencies, provisioner(), project.getProjectDir(),
 					project.getLayout().getBuildDirectory().getAsFile().get(), npmModulesCacheOrNull(),
 					new NpmPathResolver(npmFileOrNull(), nodeFileOrNull(), npmrcFileOrNull(),
 							Arrays.asList(project.getProjectDir(), project.getRootDir())),

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2024 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.
@@ -106,7 +106,7 @@ public JavascriptEslintConfig(Map<String, String> devDependencies) {
 		public FormatterStep createStep() {
 			final Project project = getProject();
 
-			return EslintFormatterStep.create(devDependencies, provisioner(), project.getProjectDir(),
+			return EslintFormatterStep.create(NAME, devDependencies, provisioner(), project.getProjectDir(),
 					project.getLayout().getBuildDirectory().getAsFile().get(), npmModulesCacheOrNull(),
 					new NpmPathResolver(npmFileOrNull(), nodeFileOrNull(), npmrcFileOrNull(),
 							Arrays.asList(project.getProjectDir(), project.getRootDir())),

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2024 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.
@@ -214,7 +214,7 @@ public TypescriptEslintConfig tsconfigFile(Object path) {
 		public FormatterStep createStep() {
 			final Project project = getProject();
 
-			return EslintFormatterStep.create(devDependencies, provisioner(), project.getProjectDir(),
+			return EslintFormatterStep.create(NAME, devDependencies, provisioner(), project.getProjectDir(),
 					project.getLayout().getBuildDirectory().getAsFile().get(), npmModulesCacheOrNull(),
 					new NpmPathResolver(npmFileOrNull(), nodeFileOrNull(), npmrcFileOrNull(),
 							Arrays.asList(project.getProjectDir(), project.getRootDir())),

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2024 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.
@@ -15,10 +15,18 @@
  */
 package com.diffplug.gradle.spotless;
 
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.File;
 import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
-import org.assertj.core.api.Assertions;
 import org.gradle.testkit.runner.BuildResult;
+import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.ValueSource;
 
@@ -51,7 +59,7 @@ void useInlineConfig(String prettierVersion) throws IOException {
 				"}");
 		setFile("test.ts").toResource("npm/prettier/config/typescript.dirty");
 		final BuildResult spotlessApply = gradleRunner().withArguments("--stacktrace", "spotlessApply").build();
-		Assertions.assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
+		assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
 		switch (prettierVersion) {
 		case PRETTIER_VERSION_2:
 			assertFile("test.ts").sameAsResource("npm/prettier/config/typescript.configfile_prettier_2.clean");
@@ -81,7 +89,7 @@ void verifyCleanSpotlessCheckWorks(String prettierVersion) throws IOException {
 				"}");
 		setFile("test.ts").toResource("npm/prettier/config/typescript.dirty");
 		final BuildResult spotlessCheckFailsGracefully = gradleRunner().withArguments("--stacktrace", "spotlessCheck").buildAndFail();
-		Assertions.assertThat(spotlessCheckFailsGracefully.getOutput()).contains("> The following files had format violations:");
+		assertThat(spotlessCheckFailsGracefully.getOutput()).contains("> The following files had format violations:");
 
 		gradleRunner().withArguments("--stacktrace", "spotlessApply").build();
 		gradleRunner().withArguments("--stacktrace", "spotlessCheck").build();
@@ -104,7 +112,7 @@ void useFileConfig(String prettierVersion) throws IOException {
 				"}");
 		setFile("test.ts").toResource("npm/prettier/config/typescript.dirty");
 		final BuildResult spotlessApply = gradleRunner().withArguments("--stacktrace", "spotlessApply").build();
-		Assertions.assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
+		assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
 		switch (prettierVersion) {
 		case PRETTIER_VERSION_2:
 			assertFile("test.ts").sameAsResource("npm/prettier/config/typescript.configfile_prettier_2.clean");
@@ -131,7 +139,7 @@ void chooseParserBasedOnFilename(String prettierVersion) throws IOException {
 				"}");
 		setFile("dirty.json").toResource("npm/prettier/filename/dirty.json");
 		final BuildResult spotlessApply = gradleRunner().withArguments("--stacktrace", "spotlessApply").build();
-		Assertions.assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
+		assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
 		assertFile("dirty.json").sameAsResource("npm/prettier/filename/clean.json");
 	}
 
@@ -169,7 +177,7 @@ void useJavaCommunityPlugin(String prettierVersion) throws IOException {
 				"}");
 		setFile("JavaTest.java").toResource("npm/prettier/plugins/java-test.dirty");
 		final BuildResult spotlessApply = gradleRunner().withArguments("--stacktrace", "spotlessApply").build();
-		Assertions.assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
+		assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
 		assertFile("JavaTest.java").sameAsResource("npm/prettier/plugins/java-test.clean");
 	}
 
@@ -202,7 +210,7 @@ void useJavaCommunityPluginFileConfig(String prettierVersion) throws IOException
 				"}");
 		setFile("JavaTest.java").toResource("npm/prettier/plugins/java-test.dirty");
 		final BuildResult spotlessApply = gradleRunner().withArguments("--stacktrace", "spotlessApply").build();
-		Assertions.assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
+		assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
 		assertFile("JavaTest.java").sameAsResource("npm/prettier/plugins/java-test.clean");
 	}
 
@@ -226,8 +234,8 @@ void suggestsMissingJavaCommunityPlugin(String prettierVersion) throws IOExcepti
 				"}");
 		setFile("JavaTest.java").toResource("npm/prettier/plugins/java-test.dirty");
 		final BuildResult spotlessApply = gradleRunner().withArguments("--stacktrace", "spotlessApply").buildAndFail();
-		Assertions.assertThat(spotlessApply.getOutput()).contains("Could not infer a parser");
-		Assertions.assertThat(spotlessApply.getOutput()).contains("prettier-plugin-java");
+		assertThat(spotlessApply.getOutput()).contains("Could not infer a parser");
+		assertThat(spotlessApply.getOutput()).contains("prettier-plugin-java");
 	}
 
 	@ParameterizedTest(name = "{index}: usePhpCommunityPlugin with prettier {0}")
@@ -264,7 +272,7 @@ void usePhpCommunityPlugin(String prettierVersion) throws IOException {
 				"}");
 		setFile("php-example.php").toResource("npm/prettier/plugins/php.dirty");
 		final BuildResult spotlessApply = gradleRunner().withArguments("--stacktrace", "spotlessApply").build();
-		Assertions.assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
+		assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
 		assertFile("php-example.php").sameAsResource("npm/prettier/plugins/php.clean");
 	}
 
@@ -324,9 +332,9 @@ void usePhpAndJavaCommunityPlugin(String prettierVersion) throws IOException {
 		setFile("php-example.php").toResource("npm/prettier/plugins/php.dirty");
 		setFile("JavaTest.java").toResource("npm/prettier/plugins/java-test.dirty");
 		final BuildResult spotlessApply = gradleRunner().forwardOutput().withArguments("--stacktrace", "--info", "spotlessApply").build();
-		Assertions.assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
+		assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
 		final BuildResult spotlessApply2 = gradleRunner().forwardOutput().withArguments("--stacktrace", "--info", "spotlessApply").build();
-		Assertions.assertThat(spotlessApply2.getOutput()).contains("BUILD SUCCESSFUL");
+		assertThat(spotlessApply2.getOutput()).contains("BUILD SUCCESSFUL");
 		assertFile("php-example.php").sameAsResource("npm/prettier/plugins/php.clean");
 		assertFile("JavaTest.java").sameAsResource("npm/prettier/plugins/java-test.clean");
 	}
@@ -355,7 +363,7 @@ void autodetectNpmrcFileConfig(String prettierVersion) throws IOException {
 				"}");
 		setFile("test.ts").toResource("npm/prettier/config/typescript.dirty");
 		final BuildResult spotlessApply = gradleRunner().withArguments("--stacktrace", "spotlessApply").buildAndFail();
-		Assertions.assertThat(spotlessApply.getOutput()).containsPattern("Running npm command.*npm install.* failed with exit code: 1");
+		assertThat(spotlessApply.getOutput()).containsPattern("Running npm command.*npm install.* failed with exit code: 1");
 	}
 
 	@ParameterizedTest(name = "{index}: verifyCleanAndSpotlessWorks with prettier {0}")
@@ -377,9 +385,9 @@ void verifyCleanAndSpotlessWorks(String prettierVersion) throws IOException {
 				"}");
 		setFile("test.ts").toResource("npm/prettier/config/typescript.dirty");
 		final BuildResult spotlessApply = gradleRunner().withArguments("--stacktrace", "clean", "spotlessApply").build();
-		Assertions.assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
+		assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
 		final BuildResult spotlessApply2 = gradleRunner().withArguments("--stacktrace", "clean", "spotlessApply").build();
-		Assertions.assertThat(spotlessApply2.getOutput()).contains("BUILD SUCCESSFUL");
+		assertThat(spotlessApply2.getOutput()).contains("BUILD SUCCESSFUL");
 	}
 
 	@ParameterizedTest(name = "{index}: verifyCleanAndSpotlessWithNpmInstallCacheWorks with prettier {0}")
@@ -401,9 +409,9 @@ void verifyCleanAndSpotlessWithNpmInstallCacheWorks(String prettierVersion) thro
 				"}");
 		setFile("test.ts").toResource("npm/prettier/config/typescript.dirty");
 		final BuildResult spotlessApply = gradleRunner().withArguments("--stacktrace", "clean", "spotlessApply").build();
-		Assertions.assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
+		assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
 		final BuildResult spotlessApply2 = gradleRunner().withArguments("--stacktrace", "clean", "spotlessApply").build();
-		Assertions.assertThat(spotlessApply2.getOutput()).contains("BUILD SUCCESSFUL");
+		assertThat(spotlessApply2.getOutput()).contains("BUILD SUCCESSFUL");
 	}
 
 	@ParameterizedTest(name = "{index}: autodetectNpmrcFileConfig with prettier {0}")
@@ -430,6 +438,51 @@ void pickupNpmrcFileConfig(String prettierVersion) throws IOException {
 				"}");
 		setFile("test.ts").toResource("npm/prettier/config/typescript.dirty");
 		final BuildResult spotlessApply = gradleRunner().withArguments("--stacktrace", "spotlessApply").buildAndFail();
-		Assertions.assertThat(spotlessApply.getOutput()).containsPattern("Running npm command.*npm install.* failed with exit code: 1");
+		assertThat(spotlessApply.getOutput()).containsPattern("Running npm command.*npm install.* failed with exit code: 1");
+	}
+
+	@Test
+	void multiplePrettierSetupsDoNotIntersectOnNpmDir() throws IOException {
+		setFile("build.gradle").toLines(
+				"plugins {",
+				"    id 'com.diffplug.spotless'",
+				"}",
+				"repositories { mavenCentral() }",
+				"def prettierConfig = [:]",
+				"prettierConfig['printWidth'] = 120",
+				"spotless {",
+				"    format 'mytypescript', {",
+				"        target 'test.ts'",
+				"        prettier().config(prettierConfig)",
+				"    }",
+				"    format 'json', {",
+				"        target 'test.json'",
+				"        prettier().config(prettierConfig)",
+				"    }",
+				"    javascript {",
+				"        target 'test.js'",
+				"        prettier().config(prettierConfig)",
+				"    }",
+				"}");
+
+		setFile("test.ts").toResource("npm/prettier/config/typescript.dirty");
+		setFile("test.json").toResource("npm/prettier/filetypes/json/json.dirty");
+		setFile("test.js").toResource("npm/prettier/filetypes/javascript-es5/javascript-es5.dirty");
+
+		final BuildResult spotlessApply = gradleRunner().withArguments("--stacktrace", "spotlessApply").build();
+		assertThat(spotlessApply.getOutput()).contains("BUILD SUCCESSFUL");
+
+		File buildFolder = new File(rootFolder(), "build");
+		assertThat(buildFolder).isNotEmptyDirectory();
+
+		// verify it contains 3 folders containing "spotless-prettier" in it (recursively) - one for each format
+		try (Stream<Path> pathStream = Files.walk(buildFolder.toPath())) {
+			List<Path> nodeModulesDirs = pathStream
+					.sorted()
+					.filter(Files::isDirectory)
+					.filter(path -> path.getFileName().toString().contains("spotless-prettier"))
+					.collect(Collectors.toList());
+			assertThat(nodeModulesDirs).hasSize(3);
+		}
 	}
 }

plugin-maven/src/main/java/com/diffplug/spotless/maven/FormatterFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2024 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.
@@ -83,12 +83,12 @@ public final Set<String> excludes() {
 		return excludes == null ? emptySet() : Sets.newHashSet(excludes);
 	}
 
-	public final Formatter newFormatter(Supplier<Iterable<File>> filesToFormat, FormatterConfig config) {
+	public final Formatter newFormatter(Supplier<Iterable<File>> filesToFormat, FormatterConfig config, int formatterIndex) {
 		Charset formatterEncoding = encoding(config);
 		LineEnding formatterLineEndings = lineEndings(config);
 		LineEnding.Policy formatterLineEndingPolicy = formatterLineEndings.createPolicy(config.getFileLocator().getBaseDir(), filesToFormat);
 
-		FormatterStepConfig stepConfig = stepConfig(formatterEncoding, config);
+		FormatterStepConfig stepConfig = stepConfig(formatterEncoding, config, formatterIndex);
 		List<FormatterStepFactory> factories = gatherStepFactories(config.getGlobalStepFactories(), stepFactories);
 
 		List<FormatterStep> formatterSteps = factories.stream()
@@ -174,8 +174,8 @@ Optional<String> ratchetFrom(FormatterConfig config) {
 		}
 	}
 
-	private FormatterStepConfig stepConfig(Charset encoding, FormatterConfig config) {
-		return new FormatterStepConfig(encoding, licenseHeaderDelimiter(), ratchetFrom(config), config.getProvisioner(), config.getFileLocator(), config.getSpotlessSetLicenseHeaderYearsFromGitHistory());
+	private FormatterStepConfig stepConfig(Charset encoding, FormatterConfig config, int formatterIndex) {
+		return new FormatterStepConfig(encoding, licenseHeaderDelimiter(), ratchetFrom(config), config.getProvisioner(), config.getFileLocator(), config.getSpotlessSetLicenseHeaderYearsFromGitHistory(), String.format("%s-%d", "formatter", formatterIndex));
 	}
 
 	private static List<FormatterStepFactory> gatherStepFactories(List<FormatterStepFactory> allGlobal, List<FormatterStepFactory> allConfigured) {

plugin-maven/src/main/java/com/diffplug/spotless/maven/FormatterStepConfig.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2020 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.
@@ -28,14 +28,16 @@ public class FormatterStepConfig {
 	private final Provisioner provisioner;
 	private final FileLocator fileLocator;
 	private final Optional<String> spotlessSetLicenseHeaderYearsFromGitHistory;
+	private final String name;
 
-	public FormatterStepConfig(Charset encoding, String licenseHeaderDelimiter, Optional<String> ratchetFrom, Provisioner provisioner, FileLocator fileLocator, Optional<String> spotlessSetLicenseHeaderYearsFromGitHistory) {
+	public FormatterStepConfig(Charset encoding, String licenseHeaderDelimiter, Optional<String> ratchetFrom, Provisioner provisioner, FileLocator fileLocator, Optional<String> spotlessSetLicenseHeaderYearsFromGitHistory, String name) {
 		this.encoding = encoding;
 		this.licenseHeaderDelimiter = licenseHeaderDelimiter;
 		this.ratchetFrom = ratchetFrom;
 		this.provisioner = provisioner;
 		this.fileLocator = fileLocator;
 		this.spotlessSetLicenseHeaderYearsFromGitHistory = spotlessSetLicenseHeaderYearsFromGitHistory;
+		this.name = name;
 	}
 
 	public Charset getEncoding() {
@@ -61,4 +63,8 @@ public FileLocator getFileLocator() {
 	public Optional<String> spotlessSetLicenseHeaderYearsFromGitHistory() {
 		return spotlessSetLicenseHeaderYearsFromGitHistory;
 	}
+
+	public String getName() {
+		return name;
+	}
 }