Add a linter rule for variable reference spacing

Summary: Adds a linter rule for spacing after the `&` token, similar to `ArcanistUnaryPrefixExpressionSpacingXHPASTLinterRule`.

Test Plan: Added test cases.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin

Differential Revision: https://secure.phabricator.com/D14602

src/__phutil_library_map__.php

@@ -373,6 +373,8 @@ phutil_register_library_map(array(
     'ArcanistUselessOverridingMethodXHPASTLinterRule' => 'lint/linter/xhpast/rules/ArcanistUselessOverridingMethodXHPASTLinterRule.php',
     'ArcanistUselessOverridingMethodXHPASTLinterRuleTestCase' => 'lint/linter/xhpast/rules/__tests__/ArcanistUselessOverridingMethodXHPASTLinterRuleTestCase.php',
     'ArcanistUserAbortException' => 'exception/usage/ArcanistUserAbortException.php',
+    'ArcanistVariableReferenceSpacingXHPASTLinterRule' => 'lint/linter/xhpast/rules/ArcanistVariableReferenceSpacingXHPASTLinterRule.php',
+    'ArcanistVariableReferenceSpacingXHPASTLinterRuleTestCase' => 'lint/linter/xhpast/rules/__tests__/ArcanistVariableReferenceSpacingXHPASTLinterRuleTestCase.php',
     'ArcanistVariableVariableXHPASTLinterRule' => 'lint/linter/xhpast/rules/ArcanistVariableVariableXHPASTLinterRule.php',
     'ArcanistVariableVariableXHPASTLinterRuleTestCase' => 'lint/linter/xhpast/rules/__tests__/ArcanistVariableVariableXHPASTLinterRuleTestCase.php',
     'ArcanistVersionWorkflow' => 'workflow/ArcanistVersionWorkflow.php',
@@ -769,6 +771,8 @@ phutil_register_library_map(array(
     'ArcanistUselessOverridingMethodXHPASTLinterRule' => 'ArcanistXHPASTLinterRule',
     'ArcanistUselessOverridingMethodXHPASTLinterRuleTestCase' => 'ArcanistXHPASTLinterRuleTestCase',
     'ArcanistUserAbortException' => 'ArcanistUsageException',
+    'ArcanistVariableReferenceSpacingXHPASTLinterRule' => 'ArcanistXHPASTLinterRule',
+    'ArcanistVariableReferenceSpacingXHPASTLinterRuleTestCase' => 'ArcanistXHPASTLinterRuleTestCase',
     'ArcanistVariableVariableXHPASTLinterRule' => 'ArcanistXHPASTLinterRule',
     'ArcanistVariableVariableXHPASTLinterRuleTestCase' => 'ArcanistXHPASTLinterRuleTestCase',
     'ArcanistVersionWorkflow' => 'ArcanistWorkflow',

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

@@ -0,0 +1,34 @@
+<?php
+
+final class ArcanistVariableReferenceSpacingXHPASTLinterRule
+  extends ArcanistXHPASTLinterRule {
+
+  const ID = 123;
+
+  public function getLintName() {
+    return pht('Variable Reference Spacing');
+  }
+
+  public function getLintSeverity() {
+    return ArcanistLintSeverity::SEVERITY_WARNING;
+  }
+
+  public function process(XHPASTNode $root) {
+    $references = $root->selectDescendantsOfType('n_VARIABLE_REFERENCE');
+
+    foreach ($references as $reference) {
+      $variable = $reference->getChildByIndex(0);
+
+      list($before, $after) = $variable->getSurroundingNonsemanticTokens();
+
+      if ($before) {
+        $this->raiseLintAtOffset(
+          head($before)->getOffset(),
+          pht('Variable references should not be prefixed with whitespace.'),
+          implode('', mpull($before, 'getValue')),
+          '');
+      }
+    }
+  }
+
+}

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

@@ -0,0 +1,11 @@
+<?php
+
+final class ArcanistVariableReferenceSpacingXHPASTLinterRuleTestCase
+  extends ArcanistXHPASTLinterRuleTestCase {
+
+  public function testLinter() {
+    $this->executeTestsInDirectory(
+      dirname(__FILE__).'/variable-reference-spacing/');
+  }
+
+}

src/lint/linter/xhpast/rules/__tests__/variable-reference-spacing/function-call.lint-test

@@ -0,0 +1,13 @@
+<?php
+$x = &some_function();
+$x = & some_function();
+$x = &
+        some_function();
+~~~~~~~~~~
+warning:3:7
+warning:4:7
+~~~~~~~~~~
+<?php
+$x = &some_function();
+$x = &some_function();
+$x = &some_function();

src/lint/linter/xhpast/rules/__tests__/variable-reference-spacing/variable.lint-test

@@ -0,0 +1,13 @@
+<?php
+$x = &$a;
+$x = & $b;
+$x = &
+        $c;
+~~~~~~~~~~
+warning:3:7
+warning:4:7
+~~~~~~~~~~
+<?php
+$x = &$a;
+$x = &$b;
+$x = &$c;