From 59dc239c891878cd7bdc176bee4c48e67ec7845f Mon Sep 17 00:00:00 2001
From: Matthew Brown <github@muglug.com>
Date: Sat, 17 Feb 2018 18:53:02 -0500
Subject: [PATCH] Fix #522 - prevent interface instantiation

---
 config.xsd                                      |  1 +
 docs/issues.md                                  |  9 +++++++++
 .../Statements/Expression/Call/NewChecker.php   | 17 ++++++++++++++++-
 tests/InterfaceTest.php                         |  6 ++++++
 4 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/config.xsd b/config.xsd
index c8075b423..765a19cc0 100644
--- a/config.xsd
+++ b/config.xsd
@@ -107,6 +107,7 @@
             <xs:element name="InaccessibleClassConstant" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="InaccessibleMethod" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="InaccessibleProperty" type="IssueHandlerType" minOccurs="0" />
+            <xs:element name="InterfaceInstantiation" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="InvalidArgument" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="InvalidArrayAccess" type="IssueHandlerType" minOccurs="0" />
             <xs:element name="InvalidArrayAssignment" type="IssueHandlerType" minOccurs="0" />
diff --git a/docs/issues.md b/docs/issues.md
index a07557ad6..7c9cf513c 100644
--- a/docs/issues.md
+++ b/docs/issues.md
@@ -251,6 +251,15 @@ class A {
 echo (new A)->foo();
 ```
 
+### InterfaceInstantiation
+
+Emitted when an attempt is made to instatiate an interface:
+
+```php
+interface I {}
+new I();
+```
+
 ### InaccessibleProperty
 
 Emitted when attempting to access a protected/private property from outside its available scope
diff --git a/src/Psalm/Checker/Statements/Expression/Call/NewChecker.php b/src/Psalm/Checker/Statements/Expression/Call/NewChecker.php
index e6d111ee6..2fbd33ca0 100644
--- a/src/Psalm/Checker/Statements/Expression/Call/NewChecker.php
+++ b/src/Psalm/Checker/Statements/Expression/Call/NewChecker.php
@@ -11,6 +11,7 @@ use Psalm\CodeLocation;
 use Psalm\Context;
 use Psalm\Issue\AbstractInstantiation;
 use Psalm\Issue\DeprecatedClass;
+use Psalm\Issue\InterfaceInstantiation;
 use Psalm\Issue\TooManyArguments;
 use Psalm\IssueBuffer;
 use Psalm\Type;
@@ -59,6 +60,20 @@ class NewChecker extends \Psalm\Checker\Statements\Expression\CallChecker
                     ) === false) {
                         return false;
                     }
+
+                    if ($codebase->interfaceExists($fq_class_name)) {
+                        if (IssueBuffer::accepts(
+                            new InterfaceInstantiation(
+                                'Interface ' . $fq_class_name . ' cannot be instantiated',
+                                new CodeLocation($statements_checker->getSource(), $stmt->class)
+                            ),
+                            $statements_checker->getSuppressedIssues()
+                        )) {
+                            return false;
+                        }
+
+                        return null;
+                    }
                 }
             } else {
                 switch ($stmt->class->parts[0]) {
@@ -106,7 +121,7 @@ class NewChecker extends \Psalm\Checker\Statements\Expression\CallChecker
 
             if (strtolower($fq_class_name) !== 'stdclass' &&
                 $context->check_classes &&
-                $codebase->classExists($fq_class_name)
+                $codebase->classlikes->classExists($fq_class_name)
             ) {
                 $storage = $project_checker->classlike_storage_provider->get($fq_class_name);
 
diff --git a/tests/InterfaceTest.php b/tests/InterfaceTest.php
index 8da595bf1..00d05d905 100644
--- a/tests/InterfaceTest.php
+++ b/tests/InterfaceTest.php
@@ -574,6 +574,12 @@ class InterfaceTest extends TestCase
                     }',
                 'error_message' => 'InvalidReturnType',
             ],
+            'interfaceInstantiation' => [
+                '<?php
+                    interface myInterface{}
+                    new myInterface();',
+                'error_message' => 'InterfaceInstantiation',
+            ],
         ];
     }
 }