Add a linter rule for interface method bodies

Summary:
`interface` methods cannot contain a body. This construct will cause a fatal error:

```
PHP Fatal error:  Interface function X::Y() cannot contain body in /home/josh/workspace/github.com/phacility/arcanist/test.php on line 4
```

Test Plan: Added unit tests.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14561

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',
+    'ArcanistInterfaceMethodBodyXHPASTLinterRule' => 'lint/linter/xhpast/rules/ArcanistInterfaceMethodBodyXHPASTLinterRule.php',
+    'ArcanistInterfaceMethodBodyXHPASTLinterRuleTestCase' => 'lint/linter/xhpast/rules/__tests__/ArcanistInterfaceMethodBodyXHPASTLinterRuleTestCase.php',
     'ArcanistInvalidDefaultParameterXHPASTLinterRule' => 'lint/linter/xhpast/rules/ArcanistInvalidDefaultParameterXHPASTLinterRule.php',
     'ArcanistInvalidDefaultParameterXHPASTLinterRuleTestCase' => 'lint/linter/xhpast/rules/__tests__/ArcanistInvalidDefaultParameterXHPASTLinterRuleTestCase.php',
     'ArcanistInvalidModifiersXHPASTLinterRule' => 'lint/linter/xhpast/rules/ArcanistInvalidModifiersXHPASTLinterRule.php',
@@ -566,6 +568,8 @@ phutil_register_library_map(array(
     'ArcanistInstallCertificateWorkflow' => 'ArcanistWorkflow',
     'ArcanistInstanceOfOperatorXHPASTLinterRule' => 'ArcanistXHPASTLinterRule',
     'ArcanistInstanceofOperatorXHPASTLinterRuleTestCase' => 'ArcanistXHPASTLinterRuleTestCase',
+    'ArcanistInterfaceMethodBodyXHPASTLinterRule' => 'ArcanistXHPASTLinterRule',
+    'ArcanistInterfaceMethodBodyXHPASTLinterRuleTestCase' => 'ArcanistXHPASTLinterRuleTestCase',
     'ArcanistInvalidDefaultParameterXHPASTLinterRule' => 'ArcanistXHPASTLinterRule',
     'ArcanistInvalidDefaultParameterXHPASTLinterRuleTestCase' => 'ArcanistXHPASTLinterRuleTestCase',
     'ArcanistInvalidModifiersXHPASTLinterRule' => 'ArcanistXHPASTLinterRule',

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

@@ -0,0 +1,33 @@
+<?php
+
+final class ArcanistInterfaceMethodBodyXHPASTLinterRule
+  extends ArcanistXHPASTLinterRule {
+
+  const ID = 114;
+
+  public function getLintName() {
+    return pht('`%s` Method Cannot Contain Body', 'interface');
+  }
+
+  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) {
+        $body = $method->getChildByIndex(5);
+
+        if ($body->getTypeName() != 'n_EMPTY') {
+          $this->raiseLintAtNode(
+            $body,
+            pht(
+              '`%s` methods cannot contain a body. This construct will '.
+              'cause a fatal error.',
+              'interface'));
+        }
+      }
+    }
+  }
+
+}

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

@@ -0,0 +1,10 @@
+<?php
+
+final class ArcanistInterfaceMethodBodyXHPASTLinterRuleTestCase
+  extends ArcanistXHPASTLinterRuleTestCase {
+
+  public function testLinter() {
+    $this->executeTestsInDirectory(dirname(__FILE__).'/interface-method-body/');
+  }
+
+}

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

@@ -0,0 +1,7 @@
+<?php
+
+interface SomeInterface {
+  public function someMethod() {}
+}
+~~~~~~~~~~
+error:4:32

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

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