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 +1,70 @@
+/**
+ * @fileoverview Align arguments in multiline function calls
+ * @author Rich Trott
+ */
+'use strict';
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+function checkArgumentAlignment(context, node) {
+
+  function isNodeFirstInLine(node, byEndLocation) {
+    const firstToken = byEndLocation === true ? context.getLastToken(node, 1) :
+      context.getTokenBefore(node);
+    const startLine = byEndLocation === true ? node.loc.end.line :
+      node.loc.start.line;
+    const endLine = firstToken ? firstToken.loc.end.line : -1;
+
+    return startLine !== endLine;
+  }
+
+  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;
+
+  const ignoreTypes = [
+    'ArrowFunctionExpression',
+    'CallExpression',
+    'FunctionExpression',
+    'ObjectExpression',
+    'TemplateLiteral'
+  ];
+
+  const args = node.arguments;
+
+  // For now, don't bother trying to validate potentially complicating things
+  // like closures. Different people will have very different ideas and it's
+  // probably best to implement configuration options.
+  if (args.some((node) => { return ignoreTypes.indexOf(node.type) !== -1; })) {
+    return;
+  }
+
+  if (!isNodeFirstInLine(node)) {
+    return;
+  }
+
+  args.slice(1).forEach((argument) => {
+    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)
+  };
+};