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);
Trott · Apr 26, 2016 · Apr 19, 2016 · Apr 27, 2016 · 4b0c0d865c4750168975544103ce4e06e947d35f · bnoordhuis
commit 4b0c0d865c4750168975544103ce4e06e947d35f
diff --git a/.eslintrc b/.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"]

diff --git a/tools/eslint-rules/align-function-arguments.js b/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)
+  };
+};