Fix #3910 - improve handling of fgetcsv

Author: muglug

docs/manipulating_code/fixing.md

@@ -225,6 +225,7 @@ C::foo("hello");
 ### MissingPropertyType
 
 Running `vendor/bin/psalter --issues=MissingPropertyType` on
+
 ```php
 <?php
 class A {

src/Psalm/Internal/Analyzer/FunctionAnalyzer.php

@@ -211,6 +211,29 @@ public static function getReturnTypeFromCallMapWithArgs(
                     // Really this should only work on instances we've created with new Foo(),
                     // but that requires more work
                     break;
+
+                case 'fgetcsv':
+                    $string_type = Type::getString();
+                    $string_type->addType(new Type\Atomic\TNull);
+                    $string_type->ignore_nullable_issues = true;
+
+                    $call_map_return_type = new Type\Union([
+                        new Type\Atomic\TNonEmptyList(
+                            $string_type
+                        ),
+                        new Type\Atomic\TFalse,
+                        new Type\Atomic\TNull
+                    ]);
+
+                    if ($codebase->config->ignore_internal_nullable_issues) {
+                        $call_map_return_type->ignore_nullable_issues = true;
+                    }
+
+                    if ($codebase->config->ignore_internal_falsable_issues) {
+                        $call_map_return_type->ignore_falsable_issues = true;
+                    }
+
+                    return $call_map_return_type;
             }
         }
 

tests/FunctionCallTest.php

@@ -1304,6 +1304,14 @@ function safeMatch(string $pattern, string $subject, ?array $matches = null, int
 
                     safeMatch("/a/", "b");'
             ],
+            'fgetcsv' => [
+                '<?php
+                    $headers = fgetcsv(fopen("test.txt", "r"));
+                    if (empty($headers)) {
+                        throw new Exception("invalid headers");
+                    }
+                    print_r(array_map("strval", $headers));'
+            ],
         ];
     }