add basename return type provider

Like dirname return type provider of #8611

src/Psalm/Internal/Provider/FunctionReturnTypeProvider.php

@@ -21,6 +21,7 @@
 use Psalm\Internal\Provider\ReturnTypeProvider\ArraySliceReturnTypeProvider;
 use Psalm\Internal\Provider\ReturnTypeProvider\ArraySpliceReturnTypeProvider;
 use Psalm\Internal\Provider\ReturnTypeProvider\ArrayUniqueReturnTypeProvider;
+use Psalm\Internal\Provider\ReturnTypeProvider\BasenameReturnTypeProvider;
 use Psalm\Internal\Provider\ReturnTypeProvider\DirnameReturnTypeProvider;
 use Psalm\Internal\Provider\ReturnTypeProvider\ExplodeReturnTypeProvider;
 use Psalm\Internal\Provider\ReturnTypeProvider\FilterVarReturnTypeProvider;
@@ -87,6 +88,7 @@ public function __construct()
         $this->registerClass(StrTrReturnTypeProvider::class);
         $this->registerClass(VersionCompareReturnTypeProvider::class);
         $this->registerClass(MktimeReturnTypeProvider::class);
+        $this->registerClass(BasenameReturnTypeProvider::class);
         $this->registerClass(DirnameReturnTypeProvider::class);
         $this->registerClass(ExplodeReturnTypeProvider::class);
         $this->registerClass(GetObjectVarsReturnTypeProvider::class);

src/Psalm/Internal/Provider/ReturnTypeProvider/BasenameReturnTypeProvider.php

@@ -0,0 +1,54 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Psalm\Internal\Provider\ReturnTypeProvider;
+
+use Psalm\Internal\Analyzer\Statements\Expression\IncludeAnalyzer;
+use Psalm\Plugin\EventHandler\Event\FunctionReturnTypeProviderEvent;
+use Psalm\Plugin\EventHandler\FunctionReturnTypeProviderInterface;
+use Psalm\Type;
+use Psalm\Type\Union;
+
+use function basename;
+use function count;
+
+/**
+ * @internal
+ */
+class BasenameReturnTypeProvider implements FunctionReturnTypeProviderInterface
+{
+    /**
+     * @return array<lowercase-string>
+     */
+    public static function getFunctionIds(): array
+    {
+        return ['basename'];
+    }
+
+    public static function getFunctionReturnType(FunctionReturnTypeProviderEvent $event): ?Union
+    {
+        $call_args = $event->getCallArgs();
+        if (count($call_args) === 0) {
+            return null;
+        }
+
+        $statements_source = $event->getStatementsSource();
+
+        $evaled_path = IncludeAnalyzer::getPathTo(
+            $call_args[0]->value,
+            null,
+            null,
+            $statements_source->getFileName(),
+            $statements_source->getCodebase()->config
+        );
+
+        if ($evaled_path === null) {
+            return Type::getString();
+        }
+
+        $basename = basename($evaled_path);
+
+        return Type::getString($basename);
+    }
+}

tests/ReturnTypeProvider/BasenameTest.php

@@ -0,0 +1,36 @@
+<?php
+
+namespace Psalm\Tests\ReturnTypeProvider;
+
+use Psalm\Tests\TestCase;
+use Psalm\Tests\Traits\ValidCodeAnalysisTestTrait;
+
+use const DIRECTORY_SEPARATOR;
+
+class BasenameTest extends TestCase
+{
+    use ValidCodeAnalysisTestTrait;
+
+    public function providerValidCodeParse(): iterable
+    {
+        $input = 'a' . DIRECTORY_SEPARATOR . 'b' . DIRECTORY_SEPARATOR . 'c';
+
+        yield 'basenameOfLiteralStringPathReturnsLiteralString' => [
+            'code' => '<?php
+                $base = basename("' . $input . '");
+            ',
+            'assertions' => [
+                '$base===' => "'c'",
+            ],
+        ];
+
+        yield 'basenameOfStringPathReturnsString' => [
+            'code' => '<?php
+                $base = basename(implode("", range("a", "c")));
+            ',
+            'assertions' => [
+                '$base===' => 'string',
+            ],
+        ];
+    }
+}