✨ feat(scalafmt): enforce version consistency in library and config file (fix #2460)

fix #2460

Author: gaeljw

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

@@ -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