Add a linter rule for curly brace array indexes

Summary: In PHP, both `$x['key']` and `$x{'key'}` can be used to access an array (see  http://stackoverflow.com/questions/8092248/php-curly-braces-in-array-notation), but the former should be preferred.

Test Plan: Added test cases.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14603

src/__phutil_library_map__.php

@@ -96,6 +96,8 @@ phutil_register_library_map(array(
     'ArcanistCppcheckLinterTestCase' => 'lint/linter/__tests__/ArcanistCppcheckLinterTestCase.php',
     'ArcanistCpplintLinter' => 'lint/linter/ArcanistCpplintLinter.php',
     'ArcanistCpplintLinterTestCase' => 'lint/linter/__tests__/ArcanistCpplintLinterTestCase.php',
+    'ArcanistCurlyBraceArrayIndexXHPASTLinterRule' => 'lint/linter/xhpast/rules/ArcanistCurlyBraceArrayIndexXHPASTLinterRule.php',
+    'ArcanistCurlyBraceArrayIndexXHPASTLinterRuleTestCase' => 'lint/linter/xhpast/rules/__tests__/ArcanistCurlyBraceArrayIndexXHPASTLinterRuleTestCase.php',
     'ArcanistDeclarationParenthesesXHPASTLinterRule' => 'lint/linter/xhpast/rules/ArcanistDeclarationParenthesesXHPASTLinterRule.php',
     'ArcanistDeclarationParenthesesXHPASTLinterRuleTestCase' => 'lint/linter/xhpast/rules/__tests__/ArcanistDeclarationParenthesesXHPASTLinterRuleTestCase.php',
     'ArcanistDefaultParametersXHPASTLinterRule' => 'lint/linter/xhpast/rules/ArcanistDefaultParametersXHPASTLinterRule.php',
@@ -502,6 +504,8 @@ phutil_register_library_map(array(
     'ArcanistCppcheckLinterTestCase' => 'ArcanistExternalLinterTestCase',
     'ArcanistCpplintLinter' => 'ArcanistExternalLinter',
     'ArcanistCpplintLinterTestCase' => 'ArcanistExternalLinterTestCase',
+    'ArcanistCurlyBraceArrayIndexXHPASTLinterRule' => 'ArcanistXHPASTLinterRule',
+    'ArcanistCurlyBraceArrayIndexXHPASTLinterRuleTestCase' => 'ArcanistXHPASTLinterRuleTestCase',
     'ArcanistDeclarationParenthesesXHPASTLinterRule' => 'ArcanistXHPASTLinterRule',
     'ArcanistDeclarationParenthesesXHPASTLinterRuleTestCase' => 'ArcanistXHPASTLinterRuleTestCase',
     'ArcanistDefaultParametersXHPASTLinterRule' => 'ArcanistXHPASTLinterRule',

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

@@ -0,0 +1,52 @@
+<?php
+
+final class ArcanistCurlyBraceArrayIndexXHPASTLinterRule
+  extends ArcanistXHPASTLinterRule {
+
+  const ID = 119;
+
+  public function getLintName() {
+    return pht('Curly Brace Array Index');
+  }
+
+  public function getLintSeverity() {
+    return ArcanistLintSeverity::SEVERITY_WARNING;
+  }
+
+  public function process(XHPASTNode $root) {
+    $index_accesses = $root->selectDescendantsOfType('n_INDEX_ACCESS');
+
+    foreach ($index_accesses as $index_access) {
+      $tokens = $index_access->getChildByIndex(1)->getTokens();
+
+      $left_brace = head($tokens)->getPrevToken();
+      while (!$left_brace->isSemantic()) {
+        $left_brace = $left_brace->getPrevToken();
+      }
+
+      $right_brace = last($tokens)->getNextToken();
+      while (!$right_brace->isSemantic()) {
+        $right_brace = $right_brace->getNextToken();
+      }
+
+      if ($left_brace->getValue() == '{' || $right_brace->getValue() == '}') {
+        $replacement = null;
+        foreach ($index_access->getTokens() as $token) {
+          if ($token === $left_brace) {
+            $replacement .= '[';
+          } else if ($token === $right_brace) {
+            $replacement .= ']';
+          } else {
+            $replacement .= $token->getValue();
+          }
+        }
+
+        $this->raiseLintAtNode(
+          $index_access,
+          pht('Use `%s` instead of `%s`.', "\$x['key']", "\$x{'key'}"),
+          $replacement);
+      }
+    }
+  }
+
+}

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

@@ -0,0 +1,11 @@
+<?php
+
+final class ArcanistCurlyBraceArrayIndexXHPASTLinterRuleTestCase
+  extends ArcanistXHPASTLinterRuleTestCase {
+
+  public function testLinter() {
+    $this->executeTestsInDirectory(
+      dirname(__FILE__).'/curly-brace-array-index/');
+  }
+
+}

src/lint/linter/xhpast/rules/__tests__/curly-brace-array-index/array.lint-test

@@ -0,0 +1,9 @@
+<?php
+$x['key'];
+$y{'key'};
+~~~~~~~~~~
+warning:3:1
+~~~~~~~~~~
+<?php
+$x['key'];
+$y['key'];

src/lint/linter/xhpast/rules/__tests__/curly-brace-array-index/nested.lint-test

@@ -0,0 +1,7 @@
+<?php
+$x[$y{'key'}];
+~~~~~~~~~~
+warning:2:4
+~~~~~~~~~~
+<?php
+$x[$y['key']];

src/lint/linter/xhpast/rules/__tests__/curly-brace-array-index/whitespace.lint-test

@@ -0,0 +1,7 @@
+<?php
+$x { 'key' /* comment */ };
+~~~~~~~~~~
+warning:2:1
+~~~~~~~~~~
+<?php
+$x [ 'key' /* comment */ ];