Add by-reference clause removal

src/Psalm/Checker/Statements/ExpressionChecker.php

@@ -608,6 +608,15 @@ class ExpressionChecker
                 }
             } else {
                 $existing_type = $context->vars_in_scope[$var_id];
+
+                // removes dependennt vars from $context
+                $context->removeDescendents(
+                    $var_id,
+                    $existing_type,
+                    $by_ref_type,
+                    $statements_checker->getFileChecker()
+                );
+
                 if ((string)$existing_type !== 'array<empty, empty>') {
                     $context->vars_in_scope[$var_id] = $by_ref_type;
                     $stmt->inferredType = $context->vars_in_scope[$var_id];

tests/TypeAlgebraTest.php

@@ -607,4 +607,29 @@ class TypeAlgebraTest extends PHPUnit_Framework_TestCase
         $file_checker = new FileChecker('somefile.php', $this->project_checker, $stmts);
         $file_checker->visitAndAnalyzeMethods();
     }
+
+    /**
+     * @return void
+     */
+    public function testByRefAssignment()
+    {
+        $stmts = self::$parser->parse('<?php
+        function foo() : void {
+            $matches = rand(0, 1) ? ["hello"] : null;
+
+            if (!$matches) {
+                return;
+            }
+
+            preg_match("/hello/", "hello dolly", $matches);
+
+            if ($matches) {
+
+            }
+        }
+        ');
+
+        $file_checker = new FileChecker('somefile.php', $this->project_checker, $stmts);
+        $file_checker->visitAndAnalyzeMethods();
+    }
 }