feat: add empty usage inspector

- closes #25

src/Inspector/CodeStyle/EmptyFunctionUsageInspector.php

@@ -0,0 +1,53 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Symblaze\MareScan\Inspector\CodeStyle;
+
+use PhpParser\Node\Expr\Empty_;
+use PhpParser\Node\Stmt;
+use PhpParser\NodeFinder;
+use SplFileInfo;
+use Symblaze\MareScan\Inspector\CodeIssue;
+use Symblaze\MareScan\Inspector\CodeLocation;
+use Symblaze\MareScan\Inspector\InspectorInterface;
+
+final class EmptyFunctionUsageInspector implements InspectorInterface
+{
+    private const string MESSAGE = 'Usage of `empty()` function is discouraged.';
+    private const string SHORT_MESSAGE = 'The `empty()` function may lead to unexpected results. Use type-safe strict comparison instead.';
+
+    public function shortName(): string
+    {
+        return 'empty_function_usage';
+    }
+
+    public function displayName(): string
+    {
+        return 'Empty function usage';
+    }
+
+    public function description(): string
+    {
+        return 'Detects the usage of `empty()` function.';
+    }
+
+    public function inspect(SplFileInfo $file, Stmt ...$statement): array
+    {
+        $result = [];
+        $nodeFinder = new NodeFinder();
+
+        $emptyFunctionNodes = $nodeFinder->findInstanceOf($statement, Empty_::class);
+        foreach ($emptyFunctionNodes as $emptyFunctionNode) {
+            $result[] = new CodeIssue(
+                message: self::MESSAGE,
+                severity: CodeIssue::SEVERITY_WARNING,
+                codeLocation: CodeLocation::fromNode($file, $emptyFunctionNode),
+                type: 'empty_function_usage',
+                shortMessage: self::SHORT_MESSAGE,
+            );
+        }
+
+        return $result;
+    }
+}

tests/Inspector/CodeStyle/EmptyFunctionUsageInspectorTest.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Symblaze\MareScan\Tests\Inspector\CodeStyle;
+
+use PHPUnit\Framework\Attributes\Test;
+use Symblaze\MareScan\Inspector\CodeStyle\EmptyFunctionUsageInspector;
+use Symblaze\MareScan\Tests\TestCase;
+
+final class EmptyFunctionUsageInspectorTest extends TestCase
+{
+    #[Test]
+    public function definition(): void
+    {
+        $sut = new EmptyFunctionUsageInspector();
+
+        $this->assertSame('empty_function_usage', $sut->shortName());
+        $this->assertSame('Empty function usage', $sut->displayName());
+        $this->assertSame('Detects the usage of `empty()` function.', $sut->description());
+    }
+
+    #[Test]
+    public function inspect_empty_usage(): void
+    {
+        $fixture = $this->fixtureInfo('code_style/empty_used_with_scalars.php');
+        $sut = new EmptyFunctionUsageInspector();
+
+        $result = $sut->inspect($fixture, ...$this->parse($fixture));
+
+        $this->assertCount(6, $result);
+    }
+}