Checkstyle error formatter - always use file path, not file description

src/Command/ErrorFormatter/CheckstyleErrorFormatter.php

@@ -104,8 +104,12 @@ private function groupByFile(AnalysisResult $analysisResult): array
 
 		/** @var \PHPStan\Analyser\Error $fileSpecificError */
 		foreach ($analysisResult->getFileSpecificErrors() as $fileSpecificError) {
+			$absolutePath = $fileSpecificError->getFilePath();
+			if ($fileSpecificError->getTraitFilePath() !== null) {
+				$absolutePath = $fileSpecificError->getTraitFilePath();
+			}
 			$relativeFilePath = $this->relativePathHelper->getRelativePath(
-				$fileSpecificError->getFile()
+				$absolutePath
 			);
 
 			$files[$relativeFilePath][] = $fileSpecificError;

tests/PHPStan/Command/ErrorFormatter/CheckstyleErrorFormatterTest.php

@@ -2,6 +2,8 @@
 
 namespace PHPStan\Command\ErrorFormatter;
 
+use PHPStan\Analyser\Error;
+use PHPStan\Command\AnalysisResult;
 use PHPStan\File\SimpleRelativePathHelper;
 use PHPStan\Testing\ErrorFormatterTestCase;
 
@@ -136,4 +138,30 @@ public function testFormatErrors(
 		$this->assertStringStartsWith('<?xml', $outputContent);
 	}
 
+	public function testTraitPath(): void
+	{
+		$formatter = new CheckstyleErrorFormatter(new SimpleRelativePathHelper(__DIR__));
+		$error = new Error(
+			'Foo',
+			__DIR__ . '/FooTrait.php (in context of class Foo)',
+			5,
+			true,
+			__DIR__ . '/Foo.php',
+			__DIR__ . '/FooTrait.php'
+		);
+		$formatter->formatErrors(new AnalysisResult(
+			[$error],
+			[],
+			[],
+			false,
+			false,
+			null
+		), $this->getOutput());
+		$this->assertXmlStringEqualsXmlString('<checkstyle>
+	<file name="FooTrait.php">
+		<error column="1" line="5" message="Foo" severity="error"/>
+	</file>
+</checkstyle>', $this->getOutputContent());
+	}
+
 }