feat: read scalafmt version from scalafmt config if not provided

CHANGES.md

@@ -11,6 +11,7 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 
 ## [Unreleased]
 ### Added
+- `scalafmt()` now reads the version from the `version` field in the scalafmt config file when no version is explicitly set in the plugin config, falling back to the built-in default only if neither is available. ([#2922](https://github.com/diffplug/spotless/pull/2922))
 - Add `javaparserVersion` option to the Cleanthat step, allowing callers to override the JavaParser version pulled in transitively by Cleanthat. ([#2903](https://github.com/diffplug/spotless/pull/2903))
 ### Fixed
 - Fix non-idempotent formatting when `importOrder()` is combined with `greclipse()`: a single catch-all group no longer strips blank lines that `greclipse()` independently inserted between import groups. ([#2914](https://github.com/diffplug/spotless/pull/2914))

lib/src/main/java/com/diffplug/spotless/scala/ScalaFmtStep.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2025 DiffPlug
+ * Copyright 2016-2026 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,7 +20,9 @@
 import java.io.Serial;
 import java.io.Serializable;
 import java.lang.reflect.Constructor;
+import java.nio.file.Files;
 import java.util.Collections;
+import java.util.Optional;
 import java.util.Set;
 
 import javax.annotation.Nullable;
@@ -54,15 +56,16 @@ public static FormatterStep create(Provisioner provisioner) {
 		return create(defaultVersion(), defaultScalaMajorVersion(), provisioner, null);
 	}
 
-	public static FormatterStep create(String version, Provisioner provisioner, @Nullable File configFile) {
+	public static FormatterStep create(@Nullable String version, Provisioner provisioner, @Nullable File configFile) {
 		return create(version, defaultScalaMajorVersion(), provisioner, configFile);
 	}
 
-	public static FormatterStep create(String version, @Nullable String scalaMajorVersion, Provisioner provisioner, @Nullable File configFile) {
+	public static FormatterStep create(@Nullable String version, @Nullable String scalaMajorVersion, Provisioner provisioner, @Nullable File configFile) {
+		String finalVersion = version != null ? version : versionFromConfig(configFile).orElse(defaultVersion());
 		String finalScalaMajorVersion = scalaMajorVersion == null ? DEFAULT_SCALA_MAJOR_VERSION : scalaMajorVersion;
 
 		return FormatterStep.create(NAME,
-				new ScalaFmtStep(JarState.promise(() -> JarState.from(MAVEN_COORDINATE + finalScalaMajorVersion + ":" + version, provisioner)), configFile),
+				new ScalaFmtStep(JarState.promise(() -> JarState.from(MAVEN_COORDINATE + finalScalaMajorVersion + ":" + finalVersion, provisioner)), configFile),
 				ScalaFmtStep::equalityState,
 				State::createFormat);
 	}
@@ -75,6 +78,22 @@ public static String defaultScalaMajorVersion() {
 		return DEFAULT_SCALA_MAJOR_VERSION;
 	}
 
+	private static Optional<String> versionFromConfig(@Nullable File configFile) {
+		try {
+			return configFile == null || !configFile.exists() ? Optional.empty()
+					: Files.readAllLines(configFile.toPath())
+							.stream()
+							.filter(line -> line.trim().startsWith("version"))
+							.findFirst()
+							.flatMap(line -> {
+								var parts = line.replaceAll("\\s", "").split("=");
+								return parts.length < 2 ? Optional.empty() : Optional.of(parts[1]);
+							});
+		} catch (IOException e) {
+			return Optional.empty();
+		}
+	}
+
 	private State equalityState() throws IOException {
 		return new State(jarState.get(), configFile);
 	}

plugin-gradle/CHANGES.md

@@ -4,6 +4,7 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 
 ## [Unreleased]
 ### Added
+- `scalafmt()` now reads the version from the `version` field in the scalafmt config file when no version is explicitly set in the plugin config, falling back to the built-in default only if neither is available. ([#2922](https://github.com/diffplug/spotless/pull/2922))
 - Add `withIndentStyle` and `withIndentSize` configuration to `tableTestFormatter` for setting the fallback indent when no `.editorconfig` is found. ([#2893](https://github.com/diffplug/spotless/pull/2893))
 - Add `javaparserVersion(...)` to `cleanthat`, allowing users to override the JavaParser version pulled in transitively by Cleanthat. ([#2903](https://github.com/diffplug/spotless/pull/2903))
 ### Fixed

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2023 DiffPlug
+ * Copyright 2016-2026 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -35,22 +35,20 @@ public ScalaExtension(SpotlessExtension spotless) {
 	}
 
 	public ScalaFmtConfig scalafmt() {
-		return scalafmt(ScalaFmtStep.defaultVersion());
+		return new ScalaFmtConfig(null);
 	}
 
 	public ScalaFmtConfig scalafmt(String version) {
-		return new ScalaFmtConfig(version);
+		return new ScalaFmtConfig(Objects.requireNonNull(version));
 	}
 
 	public class ScalaFmtConfig {
-		final String version;
-		@Nullable
-		String scalaMajorVersion;
-		@Nullable
-		Object configFile;
+		@Nullable final String version;
+		@Nullable String scalaMajorVersion;
+		@Nullable Object configFile;
 
-		ScalaFmtConfig(String version) {
-			this.version = Objects.requireNonNull(version);
+		ScalaFmtConfig(@Nullable String version) {
+			this.version = version;
 			addStep(createStep());
 		}
 

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2021 DiffPlug
+ * Copyright 2016-2026 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,6 +20,25 @@
 import org.junit.jupiter.api.Test;
 
 class ScalaExtensionTest extends GradleIntegrationHarness {
+	@Test
+	void versionFromConfig() throws IOException {
+		setFile("build.gradle").toLines(
+				"plugins {",
+				"    id 'com.diffplug.spotless'",
+				"}",
+				"repositories { mavenCentral() }",
+				"apply plugin: 'scala'",
+				"spotless {",
+				"    scala {",
+				"        scalafmt().configFile('scalafmt.conf')",
+				"    }",
+				"}");
+		setFile("scalafmt.conf").toResource("scala/scalafmt/scalafmt_newer.conf");
+		setFile("src/main/scala/basic.scala").toResource("scala/scalafmt/basic.dirty");
+		gradleRunner().withArguments("spotlessApply").build();
+		assertFile("src/main/scala/basic.scala").sameAsResource("scala/scalafmt/basic.cleanWithCustomConf_3.0.0");
+	}
+
 	@Test
 	void integration() throws IOException {
 		setFile("build.gradle").toLines(

plugin-maven/CHANGES.md

@@ -4,6 +4,7 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 
 ## [Unreleased]
 ### Added
+- `<scalafmt>` now reads the version from the `version` field in the scalafmt config file when no `<version>` is explicitly set, falling back to the built-in default only if neither is available. ([#2922](https://github.com/diffplug/spotless/pull/2922))
 - Add `<javaparserVersion>` option to `<cleanthat>`, allowing users to override the JavaParser version pulled in transitively by Cleanthat. ([#2903](https://github.com/diffplug/spotless/pull/2903))
 ### Fixed
 - Fix non-idempotent formatting when `importOrder()` is combined with `greclipse()`: a single catch-all group no longer strips blank lines that `greclipse()` independently inserted between import groups. ([#2914](https://github.com/diffplug/spotless/pull/2914))

plugin-maven/src/main/java/com/diffplug/spotless/maven/scala/Scalafmt.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2022 DiffPlug
+ * Copyright 2016-2026 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -37,9 +37,7 @@ public class Scalafmt implements FormatterStepFactory {
 
 	@Override
 	public FormatterStep newFormatterStep(FormatterStepConfig config) {
-		String scalafmtVersion = version != null ? version : ScalaFmtStep.defaultVersion();
-		String scalafmtScalaMajorVersion = scalaMajorVersion != null ? scalaMajorVersion : ScalaFmtStep.defaultScalaMajorVersion();
 		File configFile = config.getFileLocator().locateFile(file);
-		return ScalaFmtStep.create(scalafmtVersion, scalafmtScalaMajorVersion, config.getProvisioner(), configFile);
+		return ScalaFmtStep.create(version, scalaMajorVersion, config.getProvisioner(), configFile);
 	}
 }

plugin-maven/src/test/java/com/diffplug/spotless/maven/scala/ScalafmtTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2021 DiffPlug
+ * Copyright 2016-2026 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -39,6 +39,18 @@ void testScalafmtWithCustomConfig() throws Exception {
 		runTest("scala/scalafmt/basic.cleanWithCustomConf_3.0.0");
 	}
 
+	@Test
+	void testScalafmtVersionFromConfig() throws Exception {
+		setFile("scalafmt.conf").toResource("scala/scalafmt/scalafmt_newer.conf");
+
+		writePomWithScalaSteps(
+				"<scalafmt>",
+				"  <file>${project.basedir}/scalafmt.conf</file>",
+				"</scalafmt>");
+
+		runTest("scala/scalafmt/basic.cleanWithCustomConf_3.0.0");
+	}
+
 	private void runTest(String s) throws Exception {
 		String path = "src/main/scala/test.scala";
 		setFile(path).toResource("scala/scalafmt/basic.dirty");

testlib/src/main/resources/scala/scalafmt/scalafmt_newer.conf

@@ -0,0 +1,5 @@
+version = 3.11.0
+runner.dialect = scala213
+runner.dialectFeatures = [relaxedLambdaSyntax]
+style = defaultWithAlign
+maxColumn = 20

testlib/src/test/java/com/diffplug/spotless/scala/ScalaFmtStepTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016-2025 DiffPlug
+ * Copyright 2016-2026 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -88,6 +88,24 @@ protected FormatterStep create() {
 		}.testEquals();
 	}
 
+	@Test
+	void behaviorVersionFromConfigFile() {
+		StepHarness.forStep(ScalaFmtStep.create((String) null, TestProvisioner.mavenCentral(), createTestFile("scala/scalafmt/scalafmt.conf")))
+				.testResource("scala/scalafmt/basic.dirty", "scala/scalafmt/basic.cleanWithCustomConf_3.0.0");
+	}
+
+	@Test
+	void behaviorVersionFromConfigFileNewerVersion() {
+		StepHarness.forStep(ScalaFmtStep.create((String) null, TestProvisioner.mavenCentral(), createTestFile("scala/scalafmt/scalafmt_newer.conf")))
+				.testResource("scala/scalafmt/basic.dirty", "scala/scalafmt/basic.cleanWithCustomConf_3.0.0");
+	}
+
+	@Test
+	void behaviorDefaultVersionWithoutConfigFile() {
+		StepHarness.forStep(ScalaFmtStep.create((String) null, TestProvisioner.mavenCentral(), null))
+				.testResource("scala/scalafmt/basic.dirty", "scala/scalafmt/basic.clean_3.0.0");
+	}
+
 	@Test
 	void invalidConfiguration() {
 		File invalidConfFile = createTestFile("scala/scalafmt/scalafmt.invalid.conf");