Fix #728 - remove statement return type when re-analysing

src/Psalm/Checker/Statements/Expression/Call/MethodCallChecker.php

@@ -47,6 +47,8 @@ class MethodCallChecker extends \Psalm\Checker\Statements\Expression\CallChecker
         PhpParser\Node\Expr\MethodCall $stmt,
         Context $context
     ) {
+        $stmt->inferredType = null;
+
         if (ExpressionChecker::analyze($statements_checker, $stmt->var, $context) === false) {
             return false;
         }

tests/SwitchTypeTest.php

@@ -258,6 +258,26 @@ class SwitchTypeTest extends TestCase
                       }
                     }',
             ],
+            'dontResolveTypesBadly' => [
+                '<?php
+                    $a = new A;
+
+                    switch (rand(0,1)) {
+                        case 0:
+                        case 1:
+                            $dt = $a->maybeReturnsDT();
+                            if (!is_null($dt)) {
+                                $dt = $dt->format(\DateTime::ISO8601);
+                            }
+                            break;
+                    }
+
+                    class A {
+                        public function maybeReturnsDT(): ?\DateTimeInterface {
+                            return rand(0,1) ? new \DateTime("now") : null;
+                        }
+                    }',
+            ],
         ];
     }