From 8fd671bdc4535b320785a8d1d3b7f54d3934e4b3 Mon Sep 17 00:00:00 2001
From: Matthew Brown <github@muglug.com>
Date: Wed, 28 Jun 2017 23:37:02 -0400
Subject: [PATCH] Fix #167 - prevent Empty type in assignment

---
 config.xsd                                        |  1 +
 .../Statements/Expression/AssignmentChecker.php   |  3 ++-
 .../Statements/Expression/FetchChecker.php        | 13 +++++++++++++
 src/Psalm/Issue/EmptyArrayAccess.php              |  6 ++++++
 tests/ArrayAccessTest.php                         | 15 ++++++++++++---
 5 files changed, 34 insertions(+), 4 deletions(-)
 create mode 100644 src/Psalm/Issue/EmptyArrayAccess.php

diff --git a/config.xsd b/config.xsd
index 232cff023..d4120c3af 100644
--- a/config.xsd
+++ b/config.xsd
@@ -91,6 +91,7 @@
             <xs:element name="DeprecatedProperty" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="DuplicateParam" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="DuplicateClass" type="IssueHandlerType" minOccurs="0" />
+            <xs:element name="EmptyArrayAccess" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="FailedTypeResolution" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="ForbiddenCode" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="ImplicitToStringCast" type="IssueHandlerType" minOccurs="0" />
diff --git a/src/Psalm/Checker/Statements/Expression/AssignmentChecker.php b/src/Psalm/Checker/Statements/Expression/AssignmentChecker.php
index cee3f7a4a..3bb4ea333 100644
--- a/src/Psalm/Checker/Statements/Expression/AssignmentChecker.php
+++ b/src/Psalm/Checker/Statements/Expression/AssignmentChecker.php
@@ -546,7 +546,8 @@ class AssignmentChecker
                     ($lhs_type_part instanceof TNamedObject &&
                         in_array(
                             strtolower($lhs_type_part->value),
-                            ['stdclass', 'simplexmlelement', 'dateinterval', 'domdocument', 'domnode'], true
+                            ['stdclass', 'simplexmlelement', 'dateinterval', 'domdocument', 'domnode'],
+                            true
                         )
                     )
                 ) {
diff --git a/src/Psalm/Checker/Statements/Expression/FetchChecker.php b/src/Psalm/Checker/Statements/Expression/FetchChecker.php
index 8ca632ace..169b36139 100644
--- a/src/Psalm/Checker/Statements/Expression/FetchChecker.php
+++ b/src/Psalm/Checker/Statements/Expression/FetchChecker.php
@@ -12,6 +12,7 @@ use Psalm\Checker\TraitChecker;
 use Psalm\CodeLocation;
 use Psalm\Context;
 use Psalm\Issue\DeprecatedProperty;
+use Psalm\Issue\EmptyArrayAccess;
 use Psalm\Issue\InaccessibleClassConstant;
 use Psalm\Issue\InvalidArrayAccess;
 use Psalm\Issue\InvalidArrayAssignment;
@@ -1064,6 +1065,18 @@ class FetchChecker
                         }
                     } elseif ($type instanceof Type\Atomic\TArray && $value_index !== null) {
                         $stmt->inferredType = $type->type_params[$value_index];
+                        if ($stmt->inferredType->isEmpty()) {
+                            if (IssueBuffer::accepts(
+                                new EmptyArrayAccess(
+                                    'Cannot access value on empty array variable ' . $var_id,
+                                    new CodeLocation($statements_checker->getSource(), $stmt)
+                                ),
+                                $statements_checker->getSuppressedIssues()
+                            )) {
+                                return false;
+                            }
+                            $stmt->inferredType = Type::getMixed();
+                        }
                     } elseif ($type instanceof Type\Atomic\ObjectLike) {
                         $object_like_keys = array_keys($type->properties);
                         if ($object_like_keys) {
diff --git a/src/Psalm/Issue/EmptyArrayAccess.php b/src/Psalm/Issue/EmptyArrayAccess.php
new file mode 100644
index 000000000..e1b312282
--- /dev/null
+++ b/src/Psalm/Issue/EmptyArrayAccess.php
@@ -0,0 +1,6 @@
+<?php
+namespace Psalm\Issue;
+
+class EmptyArrayAccess extends CodeError
+{
+}
diff --git a/tests/ArrayAccessTest.php b/tests/ArrayAccessTest.php
index fdfb96e9b..9a9e32f30 100644
--- a/tests/ArrayAccessTest.php
+++ b/tests/ArrayAccessTest.php
@@ -43,7 +43,7 @@ class ArrayAccessTest extends TestCase
                         if ($a["bat"]) {
                             return $a["bat"];
                         }
-            
+
                         return "blah";
                     }',
             ],
@@ -56,7 +56,7 @@ class ArrayAccessTest extends TestCase
                         if ($a[0]) {
                             return $a[0];
                         }
-            
+
                         return "blah";
                     }',
             ],
@@ -64,9 +64,18 @@ class ArrayAccessTest extends TestCase
                 '<?php
                     $a = rand(0, 1) ? [1, 2] : null;
                     echo $a[0];',
-                'assertions' => [],
                 'error_levels' => ['PossiblyNullArrayAccess'],
             ],
+            'ignorePossiblyNullArrayAccess' => [
+                '<?php
+                    $arr = [];
+                    $x = $arr[0];
+                    if (isset($arr[0]) && $arr[0]) { }',
+                'assertions' => [
+                    ['mixed' => '$x'],
+                ],
+                'error_levels' => ['EmptyArrayAccess', 'MixedAssignment'],
+            ],
         ];
     }