[New] jsx-newline: Add prevent option

Fixes #2793. Closes #2927.

CHANGELOG.md

@@ -9,6 +9,7 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 * [`jsx-no-target-blank`]: add fixer ([#2862][] @Nokel81)
 * [`jsx-pascal-case`]: support minimatch `ignore` option ([#2906][] @bcherny)
 * [`jsx-pascal-case`]: support `allowNamespace` option ([#2917][] @kev-y-huang)
+* [`jsx-newline`]: Add prevent option ([#2935][] @jsphstls)
 
 ### Fixed
 * [`jsx-no-constructed-context-values`]: avoid a crash with `as X` TS code ([#2894][] @ljharb)
@@ -28,6 +29,7 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 * [Docs] added missing curly braces ([#2923][] @Muditxofficial)
 
 [#2943]: https://github.com/yannickcr/eslint-plugin-react/pull/2943
+[#2935]: https://github.com/yannickcr/eslint-plugin-react/pull/2935
 [#2930]: https://github.com/yannickcr/eslint-plugin-react/pull/2930
 [#2929]: https://github.com/yannickcr/eslint-plugin-react/pull/2929
 [#2925]: https://github.com/yannickcr/eslint-plugin-react/pull/2925

README.md

@@ -179,7 +179,7 @@ Enable the rules that you would like to use.
 | ✔ |  | [react/jsx-key](docs/rules/jsx-key.md) | Report missing `key` props in iterators/collection literals |
 |  |  | [react/jsx-max-depth](docs/rules/jsx-max-depth.md) | Validate JSX maximum depth |
 |  | 🔧 | [react/jsx-max-props-per-line](docs/rules/jsx-max-props-per-line.md) | Limit maximum of props on a single line in JSX |
-|  | 🔧 | [react/jsx-newline](docs/rules/jsx-newline.md) | Enforce a new line after jsx elements and expressions |
+|  | 🔧 | [react/jsx-newline](docs/rules/jsx-newline.md) | Require or prevent a new line after jsx elements and expressions |
 |  |  | [react/jsx-no-bind](docs/rules/jsx-no-bind.md) | Prevents usage of Function.prototype.bind and arrow functions in React component props |
 | ✔ |  | [react/jsx-no-comment-textnodes](docs/rules/jsx-no-comment-textnodes.md) | Comments inside children section of tag should be placed inside braces |
 |  |  | [react/jsx-no-constructed-context-values](docs/rules/jsx-no-constructed-context-values.md) | Prevents JSX context provider values from taking values that will cause needless rerenders. |

docs/rules/jsx-newline.md

@@ -1,12 +1,24 @@
-# Enforce a new line after jsx elements and expressions (react/jsx-newline)
+# Require or prevent a new line after jsx elements and expressions. (react/jsx-newline)
 
 **Fixable:** This rule is automatically fixable using the `--fix` flag on the command line.
 
 ## Rule Details
 
-This is a stylistic rule intended to make JSX code more readable by enforcing spaces between adjacent JSX elements and expressions.
+This is a stylistic rule intended to make JSX code more readable by requiring or preventing lines between adjacent JSX elements and expressions.
 
-Examples of **incorrect** code for this rule:
+## Rule Options
+```json
+...
+"react/jsx-new-line": [<enabled>, { "prevent": <boolean> }]
+...
+```
+
+* enabled: for enabling the rule. 0=off, 1=warn, 2=error. Defaults to 0.
+* prevent: optional boolean. If `true` prevents empty lines between adjacent JSX elements and expressions. Defaults to `false`.
+
+## Examples
+
+Examples of **incorrect** code for this rule, when configured with `{ "prevent": false }`:
 
 ```jsx
 <div>
@@ -33,7 +45,7 @@ Examples of **incorrect** code for this rule:
 </div>
 ```
 
-Examples of **correct** code for this rule:
+Examples of **correct** code for this rule, when configured with `{ "prevent": false }`:
 
 ```jsx
 <div>
@@ -60,6 +72,61 @@ Examples of **correct** code for this rule:
 </div>
 ```
 
+Examples of **incorrect** code for this rule, when configured with `{ "prevent": true }`:
+
+
+```jsx
+<div>
+  <Button>{data.label}</Button>
+
+  <List />
+
+  <Button>
+    <IconPreview />
+    Button 2
+
+    <span></span>
+  </Button>
+
+  {showSomething === true && <Something />}
+
+  <Button>Button 3</Button>
+
+  {showSomethingElse === true ? (
+    <SomethingElse />
+  ) : (
+    <ErrorMessage />
+  )}
+</div>
+```
+
+Examples of **correct** code for this rule, when configured with `{ "prevent": true }`:
+
+```jsx
+<div>
+  <Button>{data.label}</Button>
+  <List />
+</div>
+```
+
+```jsx
+<div>
+  <Button>{data.label}</Button>
+  {showSomething === true && <Something />}
+</div>
+```
+
+```jsx
+<div>
+  {showSomething === true && <Something />}
+  {showSomethingElse === true ? (
+    <SomethingElse />
+  ) : (
+    <ErrorMessage />
+  )}
+</div>
+```
+
 ## When Not To Use It
 
 You can turn this rule off if you are not concerned with spacing between your JSX elements and expressions.

lib/rules/jsx-newline.js

@@ -1,6 +1,7 @@
 /**
- * @fileoverview Enforce a new line after jsx elements and expressions.
+ * @fileoverview Require or prevent a new line after jsx elements and expressions.
  * @author Johnny Zabala
+ * @author Joseph Stiles
  */
 
 'use strict';
@@ -14,16 +15,29 @@ const docsUrl = require('../util/docsUrl');
 module.exports = {
   meta: {
     docs: {
-      description: 'Enforce a new line after jsx elements and expressions',
+      description: 'Require or prevent a new line after jsx elements and expressions.',
       category: 'Stylistic Issues',
       recommended: false,
       url: docsUrl('jsx-newline')
     },
     fixable: 'code',
 
     messages: {
-      newLine: 'JSX element should start in a new line'
-    }
+      require: 'JSX element should start in a new line',
+      prevent: 'JSX element should not start in a new line'
+    },
+    schema: [
+      {
+        type: 'object',
+        properties: {
+          prevent: {
+            default: false,
+            type: 'boolean'
+          }
+        },
+        additionalProperties: false
+      }
+    ]
   },
   create(context) {
     const jsxElementParents = new Set();
@@ -35,26 +49,44 @@ module.exports = {
             if (element.type === 'JSXElement' || element.type === 'JSXExpressionContainer') {
               const firstAdjacentSibling = elements[index + 1];
               const secondAdjacentSibling = elements[index + 2];
-              if (
-                firstAdjacentSibling
-                && secondAdjacentSibling
-                && (firstAdjacentSibling.type === 'Literal' || firstAdjacentSibling.type === 'JSXText')
-                // Check adjacent sibling has the proper amount of newlines
-                && !/\n\s*\n/.test(firstAdjacentSibling.value)
-              ) {
-                context.report({
-                  node: secondAdjacentSibling,
-                  messageId: 'newLine',
-                  fix(fixer) {
-                    return fixer.replaceText(
-                      firstAdjacentSibling,
-                      // double the last newline.
-                      sourceCode.getText(firstAdjacentSibling)
-                        .replace(/(\n)(?!.*\1)/g, '\n\n')
-                    );
-                  }
-                });
-              }
+
+              const hasSibling = firstAdjacentSibling
+              && secondAdjacentSibling
+              && (firstAdjacentSibling.type === 'Literal' || firstAdjacentSibling.type === 'JSXText');
+
+              if (!hasSibling) return;
+
+              // Check adjacent sibling has the proper amount of newlines
+              const isWithoutNewLine = !/\n\s*\n/.test(firstAdjacentSibling.value);
+
+              const prevent = !!(context.options[0] || {}).prevent;
+
+              if (isWithoutNewLine === prevent) return;
+
+              const messageId = prevent
+                ? 'prevent'
+                : 'require';
+
+              const regex = prevent
+                ? /(\n\n)(?!.*\1)/g
+                : /(\n)(?!.*\1)/g;
+
+              const replacement = prevent
+                ? '\n'
+                : '\n\n';
+
+              context.report({
+                node: secondAdjacentSibling,
+                messageId,
+                fix(fixer) {
+                  return fixer.replaceText(
+                    firstAdjacentSibling,
+                    // double or remove the last newline
+                    sourceCode.getText(firstAdjacentSibling)
+                      .replace(regex, replacement)
+                  );
+                }
+              });
             }
           });
         });