Fix #522 - prevent interface instantiation

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" />

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

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);
 

tests/InterfaceTest.php

@@ -574,6 +574,12 @@ class InterfaceTest extends TestCase
                     }',
                 'error_message' => 'InvalidReturnType',
             ],
+            'interfaceInstantiation' => [
+                '<?php
+                    interface myInterface{}
+                    new myInterface();',
+                'error_message' => 'InterfaceInstantiation',
+            ],
         ];
     }
 }