Fix getenv calls

Fixes #386

src/Psalm/CallMap.php

@@ -2484,7 +2484,7 @@ return [
 'get_defined_constants' => ['array', 'categorize='=>'bool'],
 'get_defined_functions' => ['string[][]', 'exclude_disabled='=>'bool'],
 'get_defined_vars' => ['array'],
-'getenv' => ['string|string[]', 'varname='=>'string', 'local_only='=>'bool'],
+'getenv' => ['string|string[]|false', 'varname='=>'string', 'local_only='=>'bool'],
 'get_extension_funcs' => ['array', 'extension_name'=>'string'],
 'get_headers' => ['array', 'url'=>'string', 'format='=>'int'],
 'gethostbyaddr' => ['string', 'ip_address'=>'string'],

src/Psalm/Checker/FunctionChecker.php

@@ -365,6 +365,14 @@ class FunctionChecker extends FunctionLikeChecker
             throw new \InvalidArgumentException('Function ' . $function_id . ' was not found in callmap');
         }
 
+        if ($call_map_key === 'getenv') {
+            if (count($call_args)) {
+                return new Type\Union([new Type\Atomic\TString, new Type\Atomic\TFalse]);
+            }
+
+            return new Type\Union([new Type\Atomic\TArray([new Type\Atomic\TMixed, new Type\Atomic\TString])]);
+        }
+
         if ($call_args) {
             if (in_array($call_map_key, ['str_replace', 'preg_replace', 'preg_replace_callback'], true)) {
                 if (isset($call_args[2]->value->inferredType)) {

tests/FunctionCallTest.php

@@ -396,6 +396,15 @@ class FunctionCallTest extends TestCase
 
                     a(["a" => "hello"]);',
             ],
+            'getenv' => [
+                '<?php
+                    $a = getenv();
+                    $b = getenv("some_key");',
+                'assertions' => [
+                    '$a' => 'array<mixed, string>',
+                    '$b' => 'string|false',
+                ],
+            ],
         ];
     }