From 75e2be8aec41751de50e59d5d7cc53e9326c51ab Mon Sep 17 00:00:00 2001
From: Matt Brown <github@muglug.com>
Date: Mon, 18 Jun 2018 10:07:05 -0400
Subject: [PATCH] Fix #825 - ignore falsable issues on builtin *methods*

---
 src/Psalm/CallMap.php                                    | 4 ++--
 .../Statements/Expression/Call/MethodCallChecker.php     | 3 +++
 tests/MethodCallTest.php                                 | 9 +++++++++
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/src/Psalm/CallMap.php b/src/Psalm/CallMap.php
index e5b061c7f..ccdcc4f1b 100644
--- a/src/Psalm/CallMap.php
+++ b/src/Psalm/CallMap.php
@@ -1620,7 +1620,7 @@ return [
 'DateTime::add' => ['static', 'interval'=>'DateInterval'],
 'DateTime::createFromFormat' => ['static|false', 'format'=>'string', 'time'=>'string', 'timezone='=>'DateTimeZone'],
 'DateTime::diff' => ['DateInterval', 'datetime2'=>'DateTimeInterface', 'absolute='=>'bool'],
-'DateTime::format' => ['string', 'format'=>'string'],
+'DateTime::format' => ['string|false', 'format'=>'string'],
 'DateTime::getLastErrors' => ['array'],
 'DateTime::getOffset' => ['int'],
 'DateTime::getTimestamp' => ['int'],
@@ -1639,7 +1639,7 @@ return [
 'DateTimeImmutable::createFromFormat' => ['static', 'format'=>'string', 'time'=>'string', 'timezone='=>'DateTimeZone'],
 'DateTimeImmutable::createFromMutable' => ['static', 'datetime'=>'DateTime'],
 'DateTimeImmutable::diff' => ['DateInterval', 'datetime2'=>'DateTimeInterface', 'absolute='=>'bool'],
-'DateTimeImmutable::format' => ['string', 'format'=>'string'],
+'DateTimeImmutable::format' => ['string|false', 'format'=>'string'],
 'DateTimeImmutable::getLastErrors' => ['array'],
 'DateTimeImmutable::getOffset' => ['int'],
 'DateTimeImmutable::getTimestamp' => ['int'],
diff --git a/src/Psalm/Checker/Statements/Expression/Call/MethodCallChecker.php b/src/Psalm/Checker/Statements/Expression/Call/MethodCallChecker.php
index 923799b8f..ce6935a0a 100644
--- a/src/Psalm/Checker/Statements/Expression/Call/MethodCallChecker.php
+++ b/src/Psalm/Checker/Statements/Expression/Call/MethodCallChecker.php
@@ -522,6 +522,9 @@ class MethodCallChecker extends \Psalm\Checker\Statements\Expression\CallChecker
                             $return_type_candidate = Type::parseString('string|false');
                         } else {
                             $return_type_candidate = CallMap::getReturnTypeFromCallMap($call_map_id);
+                            if ($return_type_candidate->isFalsable()) {
+                                $return_type_candidate->ignore_falsable_issues = true;
+                            }
                         }
                     }
 
diff --git a/tests/MethodCallTest.php b/tests/MethodCallTest.php
index 33f28b7e0..639227d0a 100644
--- a/tests/MethodCallTest.php
+++ b/tests/MethodCallTest.php
@@ -146,6 +146,15 @@ class MethodCallTest extends TestCase
                     '$b' => 'string|bool',
                 ],
             ],
+            'datetimeformatNotFalse' => [
+                '<?php
+                    $format = random_bytes(10);
+                    $dt = new DateTime;
+                    $formatted = $dt->format($format);
+                    if (false !== $formatted) {}
+                    function takesString(string $s) : void {}
+                    takesString($formatted);'
+            ],
         ];
     }