feat(scalafmt): enforce version consistency between library and config file (#2499)

Author: nedtwigg

CHANGES.md

@@ -20,6 +20,9 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 ### Changed
 * Bump internal dependencies for npm-based formatters ([#2542](https://github.com/diffplug/spotless/pull/2542))
 
+### Changed
+* scalafmt: enforce version consistency between the version configured in Spotless and the version declared in Scalafmt config file ([#2460](https://github.com/diffplug/spotless/issues/2460))
+
 ## [3.1.2] - 2025-05-27
 ### Fixed
 * Fix `UnsupportedOperationException` in the Gradle plugin when using `targetExcludeContent[Pattern]` ([#2487](https://github.com/diffplug/spotless/pull/2487))

lib/src/scalafmt/java/com/diffplug/spotless/glue/scalafmt/ScalafmtFormatterFunc.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2022-2024 DiffPlug
+ * Copyright 2022-2025 DiffPlug
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -21,6 +21,7 @@
 import java.nio.file.Files;
 
 import org.scalafmt.Scalafmt;
+import org.scalafmt.Versions;
 import org.scalafmt.config.ScalafmtConfig;
 import org.scalafmt.config.ScalafmtConfig$;
 
@@ -45,6 +46,16 @@ public ScalafmtFormatterFunc(FileSignature configSignature) throws Exception {
 			String configStr = new String(Files.readAllBytes(file.toPath()), StandardCharsets.UTF_8);
 			config = Scalafmt.parseHoconConfig(configStr).get();
 		}
+
+		// This check is to raise awareness to the user that the version of the config file is currently not used.
+		// Context: https://github.com/diffplug/spotless/issues/2460
+		// This check should be removed when Spotless dynamically loads the proper version of the Scalafmt library.
+		String scalafmtLibraryVersion = Versions.version();
+		if (!config.version().equals(scalafmtLibraryVersion)) {
+			throw new IllegalArgumentException(
+					"Spotless is using " + scalafmtLibraryVersion + " but the config file declares " + config.version() +
+							". Both must match. Update the version declared in the plugin's settings and/or the config file.");
+		}
 	}
 
 	@Override

plugin-gradle/CHANGES.md

@@ -13,6 +13,9 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 ### Changed
 * Bump internal dependencies for npm-based formatters ([#2542](https://github.com/diffplug/spotless/pull/2542))\
 
+### Changed
+* scalafmt: enforce version consistency between the version configured in Spotless and the version declared in Scalafmt config file ([#2460](https://github.com/diffplug/spotless/issues/2460))
+
 ## [7.0.4] - 2025-05-27
 ### Fixed
 * Fix `UnsupportedOperationException` in the Gradle plugin when using `targetExcludeContent[Pattern]` ([#2487](https://github.com/diffplug/spotless/pull/2487))

plugin-maven/CHANGES.md

@@ -13,6 +13,9 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 ### Changed
 * Bump internal dependencies for npm-based formatters ([#2542](https://github.com/diffplug/spotless/pull/2542))
 
+### Changed
+* scalafmt: enforce version consistency between the version configured in Spotless and the version declared in Scalafmt config file ([#2460](https://github.com/diffplug/spotless/issues/2460))
+
 ## [2.44.5] - 2025-05-27
 ### Changed
 * Bump default `eclipse` version to latest `4.34` -> `4.35`. ([#2458](https://github.com/diffplug/spotless/pull/2458))

testlib/src/test/java/com/diffplug/spotless/scala/ScalaFmtStepTest.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.
@@ -48,17 +48,18 @@ void behaviorFileOverride() {
 	}
 
 	@Test
-	void behaviorDefaultConfigVersion_3_0_0() {
+	void behaviorNoConfigFile() {
 		FormatterStep step = ScalaFmtStep.create("3.0.0", TestProvisioner.mavenCentral(), null);
 		StepHarness.forStep(step)
 				.testResource("scala/scalafmt/basic.dirty", "scala/scalafmt/basicPost3.0.0.clean");
 	}
 
 	@Test
-	void behaviorCustomConfigVersion_3_0_0() {
+	void behaviorConfigFileVersionDoesnotMatchLibrary() {
 		FormatterStep step = ScalaFmtStep.create("3.0.0", TestProvisioner.mavenCentral(), createTestFile("scala/scalafmt/scalafmt.conf"));
-		StepHarness.forStep(step)
-				.testResource("scala/scalafmt/basic.dirty", "scala/scalafmt/basicPost3.0.0.cleanWithCustomConf");
+		Assertions.assertThatThrownBy(() -> {
+			step.format("", new File(""));
+		}).cause().message().contains("Spotless is using 3.0.0 but the config file declares 3.8.1. Both must match. Update the version declared in the plugin's settings and/or the config file.");
 	}
 
 	@Test