Fix #110 - failure to eliminate false from array|false on isset

src/Psalm/Checker/TypeChecker.php

@@ -154,9 +154,19 @@ class TypeChecker
 
                     $clauses[] = new Clause([$base => ['isset']]);
 
-                    foreach ($key_parts as $key_part_dim) {
+                    if (count($key_parts)) {
+                        $clauses[] = new Clause([$base => ['!false']]);
+                        $clauses[] = new Clause([$base => ['!int']]);
+                    }
+
+                    foreach ($key_parts as $i => $key_part_dim) {
                         $base .= '[' . $key_part_dim . ']';
                         $clauses[] = new Clause([$base => ['isset']]);
+
+                        if ($i < count($key_parts) - 1) {
+                            $clauses[] = new Clause([$base => ['!false']]);
+                            $clauses[] = new Clause([$base => ['!int']]);
+                        }
                     }
                 } else {
                     $clauses[] = new Clause([$var => [$type]]);

tests/IssetTest.php

@@ -112,6 +112,30 @@ class IssetTest extends PHPUnit_Framework_TestCase
         $this->assertEquals('mixed', (string) $context->vars_in_scope['$foo[\'a\']']);
     }
 
+    /**
+     * @return void
+     */
+    public function testIssetKeyedOffsetOrFalse()
+    {
+        $file_checker = new FileChecker(
+            'somefile.php',
+            $this->project_checker,
+            self::$parser->parse('<?php
+            /** @return void */
+            function takesString(string $str) {}
+
+            $bar = rand(0, 1) ? ["foo" => "bar"] : false;
+
+            if (isset($bar["foo"])) {
+                takesString($bar["foo"]);
+            }
+            ')
+        );
+        $context = new Context();
+        $context->vars_in_scope['$foo'] = \Psalm\Type::getArray();
+        $file_checker->visitAndAnalyzeMethods($context);
+    }
+
     /**
      * @return void
      */