allow ReplaceRegexStep to function as a Linter, use that to improve RemoveWildcardImports (#2571)

Author: nedtwigg

CHANGES.md

@@ -24,6 +24,8 @@ We adhere to the [keepachangelog](https://keepachangelog.com/en/1.0.0/) format (
 ### Fixed
 * Fix `spaceBeforeSeparator` in Jackson formatter. ([#2103](https://github.com/diffplug/spotless/pull/2103))
 * `GitPrePushHookInstaller` uses a lock to run gracefully if it is called many times in parallel. ([#2570](https://github.com/diffplug/spotless/pull/2570))
+### Added
+* Add a `lint` mode to `ReplaceRegexStep` ([#2571](https://github.com/diffplug/spotless/pull/2571))
 
 ## [3.3.1] - 2025-07-21
 ### Fixed

lib/src/main/java/com/diffplug/spotless/Lint.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.
@@ -91,7 +91,7 @@ public ShortcutException(Lint... lints) {
 		private final List<Lint> lints;
 
 		ShortcutException(Collection<Lint> lints) {
-			super(lints.iterator().next().detail);
+			super(lints.iterator().next().toString());
 			this.lints = List.copyOf(lints);
 		}
 

lib/src/main/java/com/diffplug/spotless/generic/ReplaceRegexStep.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2016 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.
@@ -15,12 +15,16 @@
  */
 package com.diffplug.spotless.generic;
 
+import java.io.File;
 import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.List;
 import java.util.Objects;
 import java.util.regex.Pattern;
 
 import com.diffplug.spotless.FormatterFunc;
 import com.diffplug.spotless.FormatterStep;
+import com.diffplug.spotless.Lint;
 
 public final class ReplaceRegexStep {
 	// prevent direct instantiation
@@ -35,6 +39,15 @@ public static FormatterStep create(String name, String regex, String replacement
 				State::toFormatter);
 	}
 
+	public static FormatterStep lint(String name, String regex, String lintDetail) {
+		Objects.requireNonNull(name, "name");
+		Objects.requireNonNull(regex, "regex");
+		Objects.requireNonNull(lintDetail, "lintDetail");
+		return FormatterStep.createLazy(name,
+				() -> new LintState(Pattern.compile(regex, Pattern.UNIX_LINES | Pattern.MULTILINE), name, lintDetail),
+				LintState::toLinter);
+	}
+
 	private static final class State implements Serializable {
 		private static final long serialVersionUID = 1L;
 
@@ -50,4 +63,38 @@ FormatterFunc toFormatter() {
 			return raw -> regex.matcher(raw).replaceAll(replacement);
 		}
 	}
+
+	private static final class LintState implements Serializable {
+		private static final long serialVersionUID = 1L;
+
+		private final Pattern regex;
+		private final String ruleId;
+		private final String lintDetail;
+
+		LintState(Pattern regex, String ruleId, String lintDetail) {
+			this.regex = regex;
+			this.ruleId = ruleId;
+			this.lintDetail = lintDetail;
+		}
+
+		FormatterFunc toLinter() {
+			return new FormatterFunc() {
+				@Override
+				public String apply(String raw) {
+					return raw;
+				}
+
+				@Override
+				public List<Lint> lint(String raw, File file) {
+					List<Lint> lints = new ArrayList<>();
+					var matcher = regex.matcher(raw);
+					while (matcher.find()) {
+						int line = 1 + (int) raw.codePoints().limit(matcher.start()).filter(c -> c == '\n').count();
+						lints.add(Lint.atLine(line, matcher.group(0), lintDetail));
+					}
+					return lints;
+				}
+			};
+		}
+	}
 }

lib/src/main/java/com/diffplug/spotless/java/RemoveWildcardImportsStep.java

@@ -20,13 +20,17 @@
 
 /** Removes any wildcard import statements. */
 public final class RemoveWildcardImportsStep {
+
+	/**
+	 * Matches lines like 'import foo.*;' or 'import static foo.*;'.
+	 */
+	private static final String REGEX = "(?m)^import\\s+(?:static\\s+)?[^;\\n]*\\*;\\R?";
+	private static final String NAME = "removeWildcardImports";
+	private static final String ERROR = "Do not use wildcard imports (e.g. java.util.*) - replace with specific class imports (e.g. java.util.List) as 'spotlessApply' cannot auto-fix this";
+
 	private RemoveWildcardImportsStep() {}
 
 	public static FormatterStep create() {
-		// Matches lines like 'import foo.*;' or 'import static foo.*;'.
-		return ReplaceRegexStep.create(
-				"removeWildcardImports",
-				"(?m)^import\\s+(?:static\\s+)?[^;\\n]*\\*;\\R?",
-				"");
+		return ReplaceRegexStep.lint(NAME, REGEX, ERROR);
 	}
 }

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

@@ -97,7 +97,7 @@ void removeWildCardImports() throws IOException {
 				"}");
 
 		setFile("test.java").toResource("java/removewildcardimports/JavaCodeWildcardsUnformatted.test");
-		gradleRunner().withArguments("spotlessApply").build();
+		gradleRunner().withArguments("spotlessApply").buildAndFail();
 		assertFile("test.java").sameAsResource("java/removewildcardimports/JavaCodeWildcardsFormatted.test");
 	}
 

testlib/src/main/resources/java/removewildcardimports/JavaCodeNoWildcardsFormatted.test

@@ -0,0 +1,4 @@
+import java.util.List;
+import mylib.Helper;
+
+public class Test {}

testlib/src/main/resources/java/removewildcardimports/JavaCodeNoWildcardsUnformatted.test

@@ -0,0 +1,4 @@
+import java.util.List;
+import mylib.Helper;
+
+public class Test {}

testlib/src/main/resources/java/removewildcardimports/JavaCodeWildcardsFormatted.test

@@ -1,4 +1,9 @@
+import java.util.*;
+import static java.util.Collections.*;
 import java.util.List;
 import mylib.Helper;
+import io.quarkus.maven.dependency.*;
+import static io.quarkus.vertx.web.Route.HttpMethod.*;
+import static org.springframework.web.reactive.function.BodyInserters.*;
 
 public class Test {}

testlib/src/test/java/com/diffplug/spotless/generic/ReplaceRegexStepTest.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2025 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.spotless.generic;
+
+import org.junit.jupiter.api.Test;
+
+import com.diffplug.common.base.StringPrinter;
+import com.diffplug.spotless.FormatterStep;
+import com.diffplug.spotless.StepHarness;
+
+class ReplaceRegexStepTest {
+	@Test
+	void formatter() throws Exception {
+		FormatterStep step = ReplaceRegexStep.create("replace", "bad", "good");
+		StepHarness.forStep(step)
+				.test("bad bad", "good good");
+	}
+
+	@Test
+	void lint() throws Exception {
+		FormatterStep step = ReplaceRegexStep.lint("stayPositive", "(bad|awful)", "no negative words");
+		StepHarness.forStep(step)
+				.expectLintsOf(StringPrinter.buildStringFromLines(
+						"bad",
+						"oh boy",
+						"x awful y",
+						"yippeee"))
+				.toBe("L1 stayPositive(bad) no negative words",
+						"L3 stayPositive(awful) no negative words");
+	}
+}