Fix #2159 - only apply elseif conditions to vars that exist in main context

src/Psalm/Internal/Analyzer/Statements/Block/IfAnalyzer.php

@@ -1250,7 +1250,7 @@ class IfAnalyzer
                     $old_elseif_context,
                     $elseif_context,
                     false,
-                    array_keys($negated_elseif_types),
+                    array_keys(\array_intersect_key($negated_elseif_types, $pre_conditional_context->vars_in_scope)),
                     $if_scope->updated_vars
                 );
             }

tests/TypeAlgebraTest.php

@@ -931,6 +931,25 @@ class TypeAlgebraTest extends TestCase
                         return $a;
                     }',
             ],
+            'allowAssertionInElseif' => [
+                '<?php
+                class X {
+                    public bool $a = false;
+                    public bool $b = false;
+                    public bool $c = false;
+                }
+
+                function foo(X $x) : void {
+                    $a = false;
+                    if ($x->b && $x->a) {
+                    } elseif ($x->c) {
+                        $a = true;
+                    }
+
+                    if ($x->c) {}
+                    if ($a) {}
+                }'
+            ],
         ];
     }