From 8bec5fc743826fd4f9195deb8af7b97bfb004fc0 Mon Sep 17 00:00:00 2001
From: Jack Robertson <jcrobertson97@gmail.com>
Date: Mon, 26 Jul 2021 08:50:12 +0100
Subject: [PATCH 1/3] Add expected behaviour tests

---
 tests/TypeReconciliation/ReconcilerTest.php |  2 ++
 tests/TypeReconciliation/TypeTest.php       | 30 +++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/tests/TypeReconciliation/ReconcilerTest.php b/tests/TypeReconciliation/ReconcilerTest.php
index a328306d516..d122def8c55 100644
--- a/tests/TypeReconciliation/ReconcilerTest.php
+++ b/tests/TypeReconciliation/ReconcilerTest.php
@@ -110,6 +110,8 @@ public function providerTestReconcilation(): array
             'notSomeClassWithSomeClassPipeBool' => ['bool', '!SomeClass', 'SomeClass|bool'],
             'notSomeClassWithSomeClassPipeNull' => ['null', '!SomeClass', 'SomeClass|null'],
             'notSomeClassWithAPipeB' => ['B', '!A', 'A|B'],
+            'notDateTimeWithDateTimeInterface' => ['DateTimeImmutable', '!DateTime', 'DateTimeInterface'],
+            'notDateTimeImmutableWithDateTimeInterface' => ['DateTime', '!DateTimeImmutable', 'DateTimeInterface'],
 
             'myObjectWithSomeClassPipeBool' => ['SomeClass', 'SomeClass', 'SomeClass|bool'],
             'myObjectWithAPipeB' => ['A', 'A', 'A|B'],
diff --git a/tests/TypeReconciliation/TypeTest.php b/tests/TypeReconciliation/TypeTest.php
index 1565fbbd593..b354065c7be 100644
--- a/tests/TypeReconciliation/TypeTest.php
+++ b/tests/TypeReconciliation/TypeTest.php
@@ -1073,6 +1073,36 @@ function foo($arr): void {
                      */
                     function consume($input): void{}'
             ],
+            'notDateTimeWithDateTimeInterface' => [
+                '<?php
+                    function foo(\DateTimeInterface $dateTime): DateTimeInterface {
+                        $dateInterval = new DateInterval("P1D");
+
+                        if ($dateTime instanceof \DateTime) {
+                            $dateTime->add($dateInterval);
+
+                            return $dateTime;
+                        } else {
+                            return $dateTime->add($dateInterval);
+                        }
+                    }
+                ',
+            ],
+            'notDateTimeImmutableWithDateTimeInterface' => [
+                '<?php
+                    function foo(\DateTimeInterface $dateTime): DateTimeInterface {
+                        $dateInterval = new DateInterval("P1D");
+
+                        if ($dateTime instanceof \DateTimeImmutable) {
+                            return $dateTime->add($dateInterval);
+                        } else {
+                            $dateTime->add($dateInterval);
+
+                            return $dateTime;
+                        }
+                    }
+                ',
+            ],
         ];
     }
 

From 0e6160c1e0a302e68fd06ee1db7d3683cb2671f5 Mon Sep 17 00:00:00 2001
From: Jack Robertson <jcrobertson97@gmail.com>
Date: Mon, 26 Jul 2021 13:41:52 +0100
Subject: [PATCH 2/3] Update DateTimeInterface type reconciliation

---
 .../Internal/Type/NegatedAssertionReconciler.php  | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/src/Psalm/Internal/Type/NegatedAssertionReconciler.php b/src/Psalm/Internal/Type/NegatedAssertionReconciler.php
index bcd0fb30707..f091c75b598 100644
--- a/src/Psalm/Internal/Type/NegatedAssertionReconciler.php
+++ b/src/Psalm/Internal/Type/NegatedAssertionReconciler.php
@@ -208,6 +208,21 @@ public static function reconcile(
             return $existing_var_type;
         }
 
+        if (!$is_equality
+            && ($assertion === 'DateTime' || $assertion === 'DateTimeImmutable')
+            && isset($existing_var_atomic_types['DateTimeInterface'])
+        ) {
+            $existing_var_type->removeType('DateTimeInterface');
+
+            if ($assertion === 'DateTime') {
+                $existing_var_type->addType(new TNamedObject('DateTimeImmutable'));
+            } else {
+                $existing_var_type->addType(new TNamedObject('DateTime'));
+            }
+
+            return $existing_var_type;
+        }
+
         if (strtolower($assertion) === 'traversable'
             && isset($existing_var_atomic_types['iterable'])
         ) {

From c8574a63477b92574d7354550ce2ae3d928eb0d7 Mon Sep 17 00:00:00 2001
From: Jack Robertson <jcrobertson97@gmail.com>
Date: Mon, 26 Jul 2021 13:56:15 +0100
Subject: [PATCH 3/3] Simplify FQNs

---
 tests/TypeReconciliation/TypeTest.php | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/tests/TypeReconciliation/TypeTest.php b/tests/TypeReconciliation/TypeTest.php
index b354065c7be..75f42828c4f 100644
--- a/tests/TypeReconciliation/TypeTest.php
+++ b/tests/TypeReconciliation/TypeTest.php
@@ -1075,10 +1075,10 @@ function consume($input): void{}'
             ],
             'notDateTimeWithDateTimeInterface' => [
                 '<?php
-                    function foo(\DateTimeInterface $dateTime): DateTimeInterface {
+                    function foo(DateTimeInterface $dateTime): DateTimeInterface {
                         $dateInterval = new DateInterval("P1D");
 
-                        if ($dateTime instanceof \DateTime) {
+                        if ($dateTime instanceof DateTime) {
                             $dateTime->add($dateInterval);
 
                             return $dateTime;
@@ -1090,10 +1090,10 @@ function foo(\DateTimeInterface $dateTime): DateTimeInterface {
             ],
             'notDateTimeImmutableWithDateTimeInterface' => [
                 '<?php
-                    function foo(\DateTimeInterface $dateTime): DateTimeInterface {
+                    function foo(DateTimeInterface $dateTime): DateTimeInterface {
                         $dateInterval = new DateInterval("P1D");
 
-                        if ($dateTime instanceof \DateTimeImmutable) {
+                        if ($dateTime instanceof DateTimeImmutable) {
                             return $dateTime->add($dateInterval);
                         } else {
                             $dateTime->add($dateInterval);