Errors thrown by a FormatterStep are now rethrown to kill the build. …

…First cut at #46.

CHANGES.md

@@ -2,6 +2,9 @@
 
 ### Version 2.4.0-SNAPSHOT - TBD ([javadoc](https://diffplug.github.io/spotless/javadoc/snapshot/), [snapshot](https://oss.sonatype.org/content/repositories/snapshots/com/diffplug/gradle/spotless/spotless/))
 
+* If a formatter step throws an `Error` or any of its subclasses, such as the `AssertionError`s thrown by JUnit, AssertJ, etc. that error will kill the build.
+	+ See [#46](https://github.com/diffplug/spotless/issues/46) for the full details.
+
 ### Version 2.3.0 - October 27th 2016 ([javadoc](https://diffplug.github.io/spotless/javadoc/snapshot/), [jcenter](https://bintray.com/diffplug/opensource/spotless/2.3.0/view))
 
 * When `spotlessCheck` fails, the error message now contains a short diff of what is neccessary to fix the issue ([#10](https://github.com/diffplug/spotless/issues/10), thanks to Jonathan Bluett-Duncan).

src/main/java/com/diffplug/gradle/spotless/Formatter.java

@@ -109,15 +109,18 @@ String applyLineEndings(String unix, File file) {
 	 * The input must have unix line endings, and the output
 	 * is guaranteed to also have unix line endings.
 	 */
-	String applySteps(String unix, File file) {
+	String applySteps(String unix, File file) throws Error {
 		for (FormatterStep step : steps) {
 			try {
 				String formatted = step.format(unix, file);
 				// should already be unix-only, but
 				// some steps might misbehave
 				unix = LineEnding.toUnix(formatted);
+			} catch (Error e) {
+				logger.error("Step '" + step.getName() + "' found problem in '" + projectDirectory.relativize(file.toPath()) + "':\n" + e.getMessage());
+				throw e;
 			} catch (Throwable e) {
-				logger.warn("Unable to apply step " + step.getName() + " to " + projectDirectory.relativize(file.toPath()) + ": " + e.getMessage());
+				logger.warn("Unable to apply step '" + step.getName() + "' to '" + projectDirectory.relativize(file.toPath()) + "': " + e.getMessage());
 				logger.info("Exception is ", e);
 			}
 		}

src/test/java/com/diffplug/gradle/spotless/ErrorShouldRethrow.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright 2016 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.gradle.spotless;
+
+import java.io.File;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import org.gradle.testkit.runner.BuildResult;
+import org.junit.Assert;
+import org.junit.Test;
+
+import com.diffplug.common.base.CharMatcher;
+import com.diffplug.common.base.Splitter;
+import com.diffplug.common.base.StringPrinter;
+
+/** Tests the desired behavior from https://github.com/diffplug/spotless/issues/46. */
+public class ErrorShouldRethrow extends GradleIntegrationTest {
+	@Test
+	public void noSwearing() throws Exception {
+		File build = write("build.gradle",
+				"plugins {",
+				"    id 'com.diffplug.gradle.spotless'",
+				"}",
+				"spotless {",
+				"    format 'misc', {",
+				"        target file('README.md')",
+				"        custom 'no swearing', {",
+				"             if (it.toLowerCase().contains('fubar')) {",
+				"                 throw new AssertionError('No swearing!');",
+				"             }",
+				"        }",
+				"    }",
+				"}");
+		write("README.md", "This code is fubar.");
+		BuildResult result = gradleRunner().withArguments("spotlessCheck").buildAndFail();
+
+		String expectedToStartWith = StringPrinter.buildStringFromLines(
+				":spotlessMiscCheckStep 'no swearing' found problem in 'README.md':",
+				"No swearing!",
+				" FAILED",
+				"",
+				"FAILURE: Build failed with an exception.",
+				"",
+				"* Where:",
+				"Build file '" + build + "' line: 9",
+				"",
+				"* What went wrong:",
+				"Execution failed for task ':spotlessMiscCheck'.",
+				"> No swearing!");
+		int numNewlines = CharMatcher.is('\n').countIn(expectedToStartWith);
+		List<String> actualLines = Splitter.on('\n').splitToList(LineEnding.toUnix(result.getOutput()));
+		String actualStart = actualLines.subList(0, numNewlines + 1).stream().collect(Collectors.joining("\n"));
+		Assert.assertEquals(expectedToStartWith, actualStart);
+	}
+}