1 files changed, 58 insertions, 0 deletions
diff --git a/tools/eslint/lib/rules/comma-dangle.js b/tools/eslint/lib/rules/comma-dangle.js
new file mode 100644
index 0000000000..da3776d424
--- /dev/null
+++ b/tools/eslint/lib/rules/comma-dangle.js
@@ -0,0 +1,58 @@
+/**
+ * @fileoverview Rule to forbid or enforce dangling commas.
+ * @author Ian Christian Myers
+ * @copyright 2015 Mathias Schreck
+ * @copyright 2013 Ian Christian Myers
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = function (context) {
+    var allowDangle = context.options[0];
+    var forbidDangle = allowDangle !== "always-multiline" && allowDangle !== "always";
+    var UNEXPECTED_MESSAGE = "Unexpected trailing comma.";
+    var MISSING_MESSAGE = "Missing trailing comma.";
+
+    /**
+     * Checks the given node for trailing comma and reports violations.
+     * @param {ASTNode} node The node of an ObjectExpression or ArrayExpression
+     * @returns {void}
+     */
+    function checkForTrailingComma(node) {
+        var items = node.properties || node.elements,
+            length = items.length,
+            nodeIsMultiLine = node.loc.start.line !== node.loc.end.line,
+            lastItem,
+            penultimateToken,
+            hasDanglingComma;
+
+        if (length) {
+            lastItem = items[length - 1];
+            if (lastItem) {
+                penultimateToken = context.getLastToken(node, 1);
+                hasDanglingComma = penultimateToken.value === ",";
+
+                if (forbidDangle && hasDanglingComma) {
+                    context.report(lastItem, penultimateToken.loc.start, UNEXPECTED_MESSAGE);
+                } else if (allowDangle === "always-multiline") {
+                    if (hasDanglingComma && !nodeIsMultiLine) {
+                        context.report(lastItem, penultimateToken.loc.start, UNEXPECTED_MESSAGE);
+                    } else if (!hasDanglingComma && nodeIsMultiLine) {
+                        context.report(lastItem, penultimateToken.loc.end, MISSING_MESSAGE);
+                    }
+                } else if (allowDangle === "always" && !hasDanglingComma) {
+                    context.report(lastItem, lastItem.loc.end, MISSING_MESSAGE);
+                }
+            }
+        }
+    }
+
+    return {
+        "ObjectExpression": checkForTrailingComma,
+        "ArrayExpression": checkForTrailingComma
+    };
+};