Resolve a relative include against the trait file in a trait context

src/Rules/Keywords/RequireFileExistsRule.php

@@ -104,7 +104,7 @@ private function doesFileExist(string $path, Scope $scope): bool
 		$directories = array_merge(
 			[$this->currentWorkingDirectory],
 			explode(PATH_SEPARATOR, get_include_path()),
-			[dirname($scope->getFile())],
+			[dirname($this->getScopeFile($scope))],
 		);
 
 		foreach ($directories as $directory) {
@@ -116,6 +116,24 @@ private function doesFileExist(string $path, Scope $scope): bool
 		return false;
 	}
 
+	/**
+	 * The "calling script's own directory" fallback of a relative include is resolved
+	 * at compile time, so inside a trait it is the directory of the file the trait is
+	 * declared in - not the file of the class that uses it, which is what
+	 * Scope::getFile() returns in a trait context.
+	 */
+	private function getScopeFile(Scope $scope): string
+	{
+		if ($scope->isInTrait()) {
+			$traitFileName = $scope->getTraitReflection()->getFileName();
+			if ($traitFileName !== null) {
+				return $this->fileHelper->normalizePath($traitFileName);
+			}
+		}
+
+		return $scope->getFile();
+	}
+
 	private function doesFileExistForDirectory(string $path, string $workingDirectory): bool
 	{
 		$fileHelper = new FileHelper($workingDirectory);

tests/PHPStan/Rules/Keywords/RequireFileExistsRuleTest.php

@@ -158,6 +158,19 @@ public function testBug12203(): void
 		]);
 	}
 
+	public function testRelativePathInTrait(): void
+	{
+		$this->analyse([
+			__DIR__ . '/data/include-relative-in-trait/trait-dir/IncludeRelativeTrait.php',
+			__DIR__ . '/data/include-relative-in-trait/class-dir/IncludeRelativeClass.php',
+		], [
+			[
+				'Path in include() "only-in-class-dir.php" is not a file or it does not exist.',
+				15,
+			],
+		]);
+	}
+
 	public function testInFileExists(): void
 	{
 		$this->analyse([__DIR__ . '/data/include-in-file-exists.php'], []);

tests/PHPStan/Rules/Keywords/data/include-relative-in-trait/class-dir/IncludeRelativeClass.php

@@ -0,0 +1,10 @@
+<?php
+
+namespace IncludeRelativeInTrait;
+
+class IncludeRelativeClass
+{
+
+	use IncludeRelativeTrait;
+
+}

tests/PHPStan/Rules/Keywords/data/include-relative-in-trait/class-dir/only-in-class-dir.php

@@ -0,0 +1,3 @@
+<?php
+
+return ['only-in-class-dir' => true];

tests/PHPStan/Rules/Keywords/data/include-relative-in-trait/trait-dir/IncludeRelativeTrait.php

@@ -0,0 +1,18 @@
+<?php
+
+namespace IncludeRelativeInTrait;
+
+trait IncludeRelativeTrait
+{
+
+	public function relativeInTraitDir(): void
+	{
+		include 'only-in-trait-dir.php';
+	}
+
+	public function relativeInClassDir(): void
+	{
+		include 'only-in-class-dir.php';
+	}
+
+}

tests/PHPStan/Rules/Keywords/data/include-relative-in-trait/trait-dir/only-in-trait-dir.php

@@ -0,0 +1,3 @@
+<?php
+
+return ['only-in-trait-dir' => true];