Add autofix for template-no-multiple-empty-lines

Author: johanrd

README.md

@@ -234,7 +234,7 @@ rules in templates can be disabled with eslint directives with mustache or html
 | [template-no-invalid-meta](docs/rules/template-no-invalid-meta.md)                                           | disallow invalid meta tags                                                   |    |    |    |
 | [template-no-log](docs/rules/template-no-log.md)                                                             | disallow {{log}} in templates                                                |    |    |    |
 | [template-no-model-argument-in-route-templates](docs/rules/template-no-model-argument-in-route-templates.md) | disallow @model argument in route templates                                  |    | 🔧 |    |
-| [template-no-multiple-empty-lines](docs/rules/template-no-multiple-empty-lines.md)                           | disallow multiple consecutive empty lines in templates                       |    |    |    |
+| [template-no-multiple-empty-lines](docs/rules/template-no-multiple-empty-lines.md)                           | disallow multiple consecutive empty lines in templates                       |    | 🔧 |    |
 | [template-no-mut-helper](docs/rules/template-no-mut-helper.md)                                               | disallow usage of (mut) helper                                               |    |    |    |
 | [template-no-negated-comparison](docs/rules/template-no-negated-comparison.md)                               | disallow negated comparisons in templates                                    |    |    |    |
 | [template-no-negated-condition](docs/rules/template-no-negated-condition.md)                                 | disallow negated conditions in if/unless                                     |    |    |    |

docs/rules/template-no-multiple-empty-lines.md

@@ -1,5 +1,7 @@
 # ember/template-no-multiple-empty-lines
 
+🔧 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
+
 <!-- end auto-generated rule header -->
 
 Disallows multiple consecutive empty lines in templates.

lib/rules/template-no-multiple-empty-lines.js

@@ -8,7 +8,7 @@ module.exports = {
       url: 'https://github.com/ember-cli/eslint-plugin-ember/tree/master/docs/rules/template-no-multiple-empty-lines.md',
       templateMode: 'both',
     },
-    fixable: null,
+    fixable: 'whitespace',
     schema: [
       {
         type: 'object',
@@ -40,6 +40,15 @@ module.exports = {
       Program(node) {
         const text = sourceCode.getText();
         const lines = text.split('\n');
+
+        // Precompute the character offset of the start of each line.
+        const lineOffsets = [];
+        let offset = 0;
+        for (const line of lines) {
+          lineOffsets.push(offset);
+          offset += line.length + 1; // +1 for the '\n'
+        }
+
         let emptyCount = 0;
         let firstEmptyLine = -1;
 
@@ -54,6 +63,12 @@ module.exports = {
               const startLine = firstEmptyLine + max + 1;
               const endLine = index;
 
+              // Remove the excess empty lines: keep `max` empty lines,
+              // remove everything from the start of the (max+1)-th empty
+              // line to the start of the next non-empty line.
+              const rangeStart = lineOffsets[firstEmptyLine + max];
+              const rangeEnd = lineOffsets[endLine];
+
               context.report({
                 loc: {
                   start: { line: startLine + 1, column: 0 },
@@ -64,6 +79,9 @@ module.exports = {
                   max,
                   pluralizedLines: max === 1 ? 'line' : 'lines',
                 },
+                fix(fixer) {
+                  return fixer.replaceTextRange([rangeStart, rangeEnd], '');
+                },
               });
             }
             emptyCount = 0;

tests/lib/rules/template-no-multiple-empty-lines.js

@@ -60,7 +60,11 @@ r
 
       <div>World</div>
     </template>`,
-      output: null,
+      output: `<template>
+      <div>Hello</div>
+
+      <div>World</div>
+    </template>`,
       errors: [
         {
           message: 'More than 1 blank line not allowed.',
@@ -75,7 +79,11 @@ r
 
       <div>Second</div>
     </template>`,
-      output: null,
+      output: `<template>
+      <div>First</div>
+
+      <div>Second</div>
+    </template>`,
       errors: [
         {
           message: 'More than 1 blank line not allowed.',
@@ -88,7 +96,9 @@ r
 
 
 <div>bar</div></template>`,
-      output: null,
+      output: `<template><div>foo</div>
+
+<div>bar</div></template>`,
       errors: [{ message: 'More than 1 blank line not allowed.' }],
     },
     {
@@ -98,7 +108,9 @@ r
 
 
 <div>bar</div></template>`,
-      output: null,
+      output: `<template><div>foo</div>
+
+<div>bar</div></template>`,
       errors: [{ message: 'More than 1 blank line not allowed.' }],
     },
   ],
@@ -142,7 +154,9 @@ hbsRuleTester.run('template-no-multiple-empty-lines', rule, {
 
 
 <div>bar</div>`,
-      output: null,
+      output: `<div>foo</div>
+
+<div>bar</div>`,
       errors: [{ message: 'More than 1 blank line not allowed.' }],
     },
     {
@@ -152,12 +166,14 @@ hbsRuleTester.run('template-no-multiple-empty-lines', rule, {
 
 
 <div>bar</div>`,
-      output: null,
+      output: `<div>foo</div>
+
+<div>bar</div>`,
       errors: [{ message: 'More than 1 blank line not allowed.' }],
     },
     {
       code: '<div>foo</div>\n\n\n\n\n<div>bar</div>',
-      output: null,
+      output: '<div>foo</div>\n\n\n\n<div>bar</div>',
       options: [{ max: 3 }],
       errors: [{ message: 'More than 3 blank lines not allowed.' }],
     },