tools: lint for alignment of variable assignments

Enforce alignment/indentation on variable assignments that span multiple
lines.
PR-URL: #6242
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: Trott

.eslintrc

@@ -13,7 +13,7 @@ rules:
  no-duplicate-case: 2
  no-empty-character-class: 2
  no-ex-assign: 2
- no-extra-boolean-cast: 2
+ no-extra-boolean-cast: 2
  no-extra-parens: [2, "functions"]
  no-extra-semi: 2
  no-func-assign: 2
@@ -86,7 +86,7 @@ rules:
 
  # Custom rules in tools/eslint-rules
  new-with-error: [2, "Error", "RangeError", "TypeError", "SyntaxError", "ReferenceError"]
-
+ align-multiline-assignment: 2
 
 # Global scoped method and vars
 globals:

tools/eslint-rules/align-multiline-assignment.js

@@ -0,0 +1,67 @@
+/**
+ * @fileoverview Align multiline variable assignments
+ * @author Rich Trott
+ */
+'use strict';
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+functiongetBinaryExpressionStarts(binaryExpression,starts){
+functiongetStartsFromOneSide(side,starts){
+starts.push(side.loc.start);
+if(side.type==='BinaryExpression'){
+starts=getBinaryExpressionStarts(side,starts);
+}
+returnstarts;
+}
+
+starts=getStartsFromOneSide(binaryExpression.left,starts);
+starts=getStartsFromOneSide(binaryExpression.right,starts);
+returnstarts;
+}
+
+functioncheckExpressionAlignment(expression){
+if(!expression)
+return;
+
+varmsg='';
+
+switch(expression.type){
+case'BinaryExpression':
+varstarts=getBinaryExpressionStarts(expression,[]);
+varstartLine=starts[0].line;
+conststartColumn=starts[0].column;
+starts.forEach((loc)=>{
+if(loc.line>startLine){
+startLine=loc.line;
+if(loc.column!==startColumn){
+msg='Misaligned multiline assignment';
+}
+}
+});
+break;
+}
+returnmsg;
+}
+
+functiontestAssignment(context,node){
+constmsg=checkExpressionAlignment(node.right);
+if(msg)
+context.report(node,msg);
+}
+
+functiontestDeclaration(context,node){
+node.declarations.forEach((declaration)=>{
+constmsg=checkExpressionAlignment(declaration.init);
+if(msg)
+context.report(node,msg);
+});
+}
+
+module.exports=function(context){
+return{
+'AssignmentExpression': (node)=>testAssignment(context,node),
+'VariableDeclaration': (node)=>testDeclaration(context,node)
+};
+};