Setup mutation testing

.github/workflows/build.yml

@@ -145,6 +145,55 @@ jobs:
       - name: "Tests"
         run: "make tests"
 
+  mutation-testing:
+    name: "Mutation Testing"
+    runs-on: "ubuntu-latest"
+    needs: ["tests", "static-analysis"]
+
+    strategy:
+      fail-fast: false
+      matrix:
+        php-version:
+          - "8.2"
+          - "8.3"
+          - "8.4"
+
+    steps:
+      - name: "Checkout"
+        uses: actions/checkout@v5
+
+      - name: "Install PHP"
+        uses: "shivammathur/setup-php@v2"
+        with:
+          coverage: "pcov"
+          php-version: "${{ matrix.php-version }}"
+          ini-file: development
+          extensions: pdo, mysqli, pgsql, pdo_mysql, pdo_pgsql, pdo_sqlite, mongodb
+          tools: infection:0.31.4
+
+      - name: "Allow installing on PHP 8.4"
+        if: matrix.php-version == '8.4'
+        run: "composer config platform.php 8.3.99"
+
+      - name: "Install dependencies"
+        run: "composer install --no-interaction --no-progress"
+
+      - uses: "actions/download-artifact@v4"
+        with:
+          name: "result-cache-${{ matrix.php-version }}"
+          path: "tmp/"
+
+      - name: "Run infection"
+        run: |
+          git fetch --depth=1 origin $GITHUB_BASE_REF
+          infection --git-diff-base=origin/$GITHUB_BASE_REF --git-diff-lines --ignore-msi-with-no-mutations --min-msi=100 --min-covered-msi=100 --log-verbosity=all --debug
+
+      - uses: "actions/upload-artifact@v4"
+        if: always()
+        with:
+          name: "infection-log-${{ matrix.php-version }}"
+          path: "tmp/infection.log"
+
   static-analysis:
     name: "PHPStan"
     runs-on: "ubuntu-latest"
@@ -189,3 +238,9 @@ jobs:
 
       - name: "PHPStan"
         run: "make phpstan"
+
+      - uses: "actions/upload-artifact@v4"
+        with:
+          # "update-packages" is not relevant for the download-artifact counterpart, but we need it here to get unique artifact names across all jobs
+          name: "result-cache-${{ matrix.php-version }}${{ matrix.update-packages && '-packages-updated' || '' }}"
+          path: "tmp/resultCache.php"

infection.json5

@@ -0,0 +1,17 @@
+{
+  "$schema": "vendor/infection/infection/resources/schema.json",
+  "timeout": 30,
+  "source": {
+    "directories": [
+      "src"
+    ]
+  },
+  "staticAnalysisTool": "phpstan",
+  "logs": {
+    "text": "tmp/infection.log"
+  },
+  "mutators": {
+    "@default": false,
+    "PHPStan\\Infection\\TrinaryLogicMutator": true
+  }
+}

phpstan.neon

@@ -18,11 +18,14 @@ parameters:
 		- src
 		- tests
 
+	resultCachePath: tmp/resultCache.php
+
 	excludePaths:
 		- tests/*/data/*
 		- tests/*/data-attributes/*
 		- tests/*/data-php-*/*
 		- tests/Rules/Doctrine/ORM/entity-manager.php
+		- tests/Infection/
 
 	reportUnmatchedIgnoredErrors: false
 

tests/Infection/TrinaryLogicMutator.php

@@ -0,0 +1,69 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Infection;
+
+use Infection\Mutator\Definition;
+use Infection\Mutator\Mutator;
+use Infection\Mutator\MutatorCategory;
+use LogicException;
+use PhpParser\Node;
+use function in_array;
+
+/**
+ * @implements Mutator<Node\Expr\MethodCall>
+ */
+final class TrinaryLogicMutator implements Mutator
+{
+
+	public static function getDefinition(): Definition
+	{
+		return new Definition(
+			<<<'TXT'
+				Replaces TrinaryLogic->yes() with !TrinaryLogic->no() and vice versa.
+				TXT
+			,
+			MutatorCategory::ORTHOGONAL_REPLACEMENT,
+			null,
+			<<<'DIFF'
+				- $type->isBoolean()->yes();
+				+ !$type->isBoolean()->no();
+			DIFF,
+		);
+	}
+
+	public function getName(): string
+	{
+		return 'TrinaryLogicMutator';
+	}
+
+	public function canMutate(Node $node): bool
+	{
+		if (!$node instanceof Node\Expr\MethodCall) {
+			return false;
+		}
+
+		if (!$node->name instanceof Node\Identifier) {
+			return false;
+		}
+
+		if (!in_array($node->name->name, ['yes', 'no'], true)) {
+			return false;
+		}
+
+		return true;
+	}
+
+	public function mutate(Node $node): iterable
+	{
+		if (!$node->name instanceof Node\Identifier) {
+			throw new LogicException();
+		}
+
+		if ($node->name->name === 'yes') {
+			yield new Node\Expr\BooleanNot(new Node\Expr\MethodCall($node->var, 'no'));
+		} else {
+			yield new Node\Expr\BooleanNot(new Node\Expr\MethodCall($node->var, 'yes'));
+		}
+	}
+
+}