Set get_post()'s return type

extension.neon

@@ -15,6 +15,10 @@ services:
         class: PHPStan\WordPress\EscSqlDynamicFunctionReturnTypeExtension
         tags:
             - phpstan.broker.dynamicFunctionReturnTypeExtension
+    -
+        class: PHPStan\WordPress\GetPostDynamicFunctionReturnTypeExtension
+        tags:
+            - phpstan.broker.dynamicFunctionReturnTypeExtension
 parameters:
     autoload_files:
         - %rootDir%/../../giacocorsiglia/wordpress-stubs/wordpress-stubs.php

src/GetPostDynamicFunctionReturnTypeExtension.php

@@ -1,5 +1,44 @@
-<?php
+<?php declare(strict_types = 1);
 /**
  * Set return type of get_post().
- * TODO https://developer.wordpress.org/reference/functions/get_post/
- */
+ */
+
+namespace PHPStan\WordPress;
+
+use PhpParser\Node\Expr\FuncCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Reflection\FunctionReflection;
+use PHPStan\Type\DynamicFunctionReturnTypeExtension;
+use PHPStan\Type\Type;
+use PHPStan\Type\ArrayType;
+use PHPStan\Type\StringType;
+use PHPStan\Type\IntegerType;
+use PHPStan\Type\MixedType;
+use PHPStan\Type\ObjectType;
+use PHPStan\Type\NullType;
+use PHPStan\Type\TypeCombinator;
+
+class GetPostDynamicFunctionReturnTypeExtension implements DynamicFunctionReturnTypeExtension
+{
+	public function isFunctionSupported(FunctionReflection $functionReflection): bool
+	{
+		return $functionReflection->getName() === 'get_post';
+	}
+
+	public function getTypeFromFunctionCall(FunctionReflection $functionReflection, FuncCall $functionCall, Scope $scope): Type
+	{
+		$output = 'OBJECT';
+		$argsCount = count($functionCall->args);
+		if ($argsCount >= 2 && $functionCall->args[1]->value !== 'OBJECT') {
+    		$output = $functionCall->args[1]->value;
+		}
+		if ($output === 'ARRAY_A') {
+			return TypeCombinator::union(new ArrayType(new StringType(), new MixedType()), new NullType());
+		}
+		if ($output === 'ARRAY_N') {
+			return TypeCombinator::union(new ArrayType(new IntegerType(), new MixedType()), new NullType());
+		}
+
+		return TypeCombinator::union(new ObjectType('WP_Post'), new NullType());
+	}
+}