tools: lint for function argument alignment

In function calls that span multiple lines, apply a custom lint rule to
enforce argument alignment.

With this rule, the following code will be flagged as an error by the
linter because the arguments on the second line start in a different
column than on the first line:

    myFunction(a, b,
      c, d);

The following code will not be flagged as an error by the linter:

    myFunction(a, b,
               c, d);

Author: Trott

.eslintrc

@@ -85,6 +85,7 @@ rules:
   prefer-const: 2
 
   # Custom rules in tools/eslint-rules
+  align-function-arguments: 2
   align-multiline-assignment: 2
   assert-fail-single-argument: 2
   new-with-error: [2, "Error", "RangeError", "TypeError", "SyntaxError", "ReferenceError"]

tools/eslint-rules/align-function-arguments.js

@@ -0,0 +1,44 @@
+/**
+ * @fileoverview Align arguments in multiline function calls
+ * @author Rich Trott
+ */
+'use strict';
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+function checkArgumentAlignment(context, node) {
+  if (node.arguments.length === 0)
+    return;
+
+  var msg = '';
+  const first = node.arguments[0];
+  var currentLine = first.loc.start.line;
+  const firstColumn = first.loc.start.column;
+
+  node.arguments.slice(1).forEach((argument) => {
+    if (argument.loc.start.line > currentLine) {
+      // Ignore if there are multiple lines between arguments. This happens
+      // in situations like this:
+      //    setTimeout(function() {
+      //      ... do stuff ...
+      //    }, 1);
+      if (argument.loc.start.line === currentLine + 1) {
+        if (argument.loc.start.column !== firstColumn) {
+          msg = 'Function called with argument in column ' +
+                `${argument.loc.start.column}, expected in ${firstColumn}`;
+        }
+      }
+      currentLine = argument.loc.start.line;
+    }
+  });
+
+  if (msg)
+    context.report(node, msg);
+}
+
+module.exports = function(context) {
+  return {
+    'CallExpression': (node) => checkArgumentAlignment(context, node)
+  };
+};