Add a linter rule for abstract methods within an interface

Summary:
`interface`s cannot contain `abstract` methods. This construct will cause a PHP fatal error:

```
Access type for interface method SomeInterface::someMethod() must be omitted
```

Test Plan: Added test cases.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14562

src/__phutil_library_map__.php

@@ -178,6 +178,8 @@ phutil_register_library_map(array(
     'ArcanistInstallCertificateWorkflow' => 'workflow/ArcanistInstallCertificateWorkflow.php',
     'ArcanistInstanceOfOperatorXHPASTLinterRule' => 'lint/linter/xhpast/rules/ArcanistInstanceOfOperatorXHPASTLinterRule.php',
     'ArcanistInstanceofOperatorXHPASTLinterRuleTestCase' => 'lint/linter/xhpast/rules/__tests__/ArcanistInstanceofOperatorXHPASTLinterRuleTestCase.php',
+    'ArcanistInterfaceAbstractMethodXHPASTLinterRule' => 'lint/linter/xhpast/rules/ArcanistInterfaceAbstractMethodXHPASTLinterRule.php',
+    'ArcanistInterfaceAbstractMethodXHPASTLinterRuleTestCase' => 'lint/linter/xhpast/rules/__tests__/ArcanistInterfaceAbstractMethodXHPASTLinterRuleTestCase.php',
     'ArcanistInterfaceMethodBodyXHPASTLinterRule' => 'lint/linter/xhpast/rules/ArcanistInterfaceMethodBodyXHPASTLinterRule.php',
     'ArcanistInterfaceMethodBodyXHPASTLinterRuleTestCase' => 'lint/linter/xhpast/rules/__tests__/ArcanistInterfaceMethodBodyXHPASTLinterRuleTestCase.php',
     'ArcanistInvalidDefaultParameterXHPASTLinterRule' => 'lint/linter/xhpast/rules/ArcanistInvalidDefaultParameterXHPASTLinterRule.php',
@@ -568,6 +570,8 @@ phutil_register_library_map(array(
     'ArcanistInstallCertificateWorkflow' => 'ArcanistWorkflow',
     'ArcanistInstanceOfOperatorXHPASTLinterRule' => 'ArcanistXHPASTLinterRule',
     'ArcanistInstanceofOperatorXHPASTLinterRuleTestCase' => 'ArcanistXHPASTLinterRuleTestCase',
+    'ArcanistInterfaceAbstractMethodXHPASTLinterRule' => 'ArcanistXHPASTLinterRule',
+    'ArcanistInterfaceAbstractMethodXHPASTLinterRuleTestCase' => 'ArcanistXHPASTLinterRuleTestCase',
     'ArcanistInterfaceMethodBodyXHPASTLinterRule' => 'ArcanistXHPASTLinterRule',
     'ArcanistInterfaceMethodBodyXHPASTLinterRuleTestCase' => 'ArcanistXHPASTLinterRuleTestCase',
     'ArcanistInvalidDefaultParameterXHPASTLinterRule' => 'ArcanistXHPASTLinterRule',

src/lint/linter/xhpast/rules/ArcanistInterfaceAbstractMethodXHPASTLinterRule.php

@@ -0,0 +1,34 @@
+<?php
+
+final class ArcanistInterfaceAbstractMethodXHPASTLinterRule
+  extends ArcanistXHPASTLinterRule {
+
+  const ID = 114;
+
+  public function getLintName() {
+    return pht('`%s` Methods Cannot Be Marked `%s`', 'interface', 'abstract');
+  }
+
+  public function process(XHPASTNode $root) {
+    $interfaces = $root->selectDescendantsOfType('n_INTERFACE_DECLARATION');
+
+    foreach ($interfaces as $interface) {
+      $methods = $interface->selectDescendantsOfType('n_METHOD_DECLARATION');
+
+      foreach ($methods as $method) {
+        $modifiers = $this->getModifiers($method);
+
+        if (idx($modifiers, 'abstract')) {
+          $this->raiseLintAtNode(
+            $method,
+            pht(
+              '`%s` methods cannot be marked as `%s`. This construct will '.
+              'cause a fatal error.',
+              'interface',
+              'abstract'));
+        }
+      }
+    }
+  }
+
+}

src/lint/linter/xhpast/rules/__tests__/ArcanistInterfaceAbstractMethodXHPASTLinterRuleTestCase.php

@@ -0,0 +1,11 @@
+<?php
+
+final class ArcanistInterfaceAbstractMethodXHPASTLinterRuleTestCase
+  extends ArcanistXHPASTLinterRuleTestCase {
+
+  public function testLinter() {
+    $this->executeTestsInDirectory(
+      dirname(__FILE__).'/interface-abstract-method/');
+  }
+
+}

src/lint/linter/xhpast/rules/__tests__/interface-abstract-method/abstract.lint-test

@@ -0,0 +1,7 @@
+<?php
+
+interface SomeInterface {
+  abstract public function someMethod();
+}
+~~~~~~~~~~
+error:4:3

src/lint/linter/xhpast/rules/__tests__/interface-abstract-method/no-abstract.lint-test

@@ -0,0 +1,6 @@
+<?php
+
+interface SomeInterface {
+  public function someMethod();
+}
+~~~~~~~~~~