[New] jsx-pascal-case: add allowLeadingUnderscore option

Author: mwaddell

CHANGELOG.md

@@ -9,6 +9,7 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 * [`jsx-no-useless-fragments`]: add option to allow single expressions in fragments ([#3006][] @mattdarveniza)
 * add [`prefer-exact-props`] rule ([#1547][] @jomasti)
 * [`jsx-no-target-blank`]: add `forms` option ([#1617][] @jaaberg)
+* [`jsx-pascal-case`]: add `allowLeadingUnderscore` option ([#3039][] @pangaeatech)
 
 ### Fixed
 * component detection: use `estraverse` to improve component detection ([#2992][] @Wesitos)
@@ -25,6 +26,7 @@ This change log adheres to standards from [Keep a CHANGELOG](http://keepachangel
 * [Docs] [`require-default-props`]: fix small typo ([#2994][] @evsasse)
 * [Tests] add weekly scheduled smoke tests ([#2963][] @AriPerkkio)
 
+[#3039]: https://github.com/yannickcr/eslint-plugin-react/pull/3039
 [#3038]: https://github.com/yannickcr/eslint-plugin-react/pull/3038
 [#3036]: https://github.com/yannickcr/eslint-plugin-react/issues/3036
 [#3026]: https://github.com/yannickcr/eslint-plugin-react/pull/3026

docs/rules/jsx-pascal-case.md

@@ -40,12 +40,13 @@ Examples of **correct** code for this rule:
 
 ```js
 ...
-"react/jsx-pascal-case": [<enabled>, { allowAllCaps: <allowAllCaps>, allowNamespace: <allowNamespace>, ignore: <ignore> }]
+"react/jsx-pascal-case": [<enabled>, { allowAllCaps: <allowAllCaps>, allowNamespace: <allowNamespace>, allowLeadingUnderscore: <allowLeadingUnderscore>, ignore: <ignore> }]
 ...
 ```
 
 * `enabled`: for enabling the rule. 0=off, 1=warn, 2=error. Defaults to 0.
 * `allowAllCaps`: optional boolean set to `true` to allow components name in all caps (default to `false`).
+* `allowLeadingUnderscore`: optional boolean set to `true` to allow components name with that starts with an underscore (default to `false`).
 * `allowNamespace`: optional boolean set to `true` to ignore namespaced components (default to `false`).
 * `ignore`: optional string-array of component names to ignore during validation (supports [minimatch](https://github.com/isaacs/minimatch)-style globs).
 
@@ -67,6 +68,19 @@ Examples of **correct** code for this rule, when `allowNamespace` is `true`:
 <TestComponent.p />
 ```
 
+### `allowLeadingUnderscore`
+
+Examples of **correct** code for this rule, when `allowLeadingUnderscore` is `true`:
+
+```jsx
+<_AllowedComponent />
+<_AllowedComponent>
+  <div />
+</_AllowedComponent>
+```
+
+**WARNING:** Adding a leading underscore to the name of a component does **NOT** affect the visibilty or accessibility of that component.  Attempting to use leading underscores to enforce privacy of your components is an error.
+
 ## When Not To Use It
 
 If you are not using JSX.

lib/rules/jsx-pascal-case.js

@@ -90,6 +90,9 @@ module.exports = {
         allowAllCaps: {
           type: 'boolean'
         },
+        allowLeadingUnderscore: {
+          type: 'boolean'
+        },
         allowNamespace: {
           type: 'boolean'
         },
@@ -111,6 +114,7 @@ module.exports = {
   create(context) {
     const configuration = context.options[0] || {};
     const allowAllCaps = configuration.allowAllCaps || false;
+    const allowLeadingUnderscore = configuration.allowLeadingUnderscore || false;
     const allowNamespace = configuration.allowNamespace || false;
     const ignore = configuration.ignore || [];
 
@@ -132,10 +136,12 @@ module.exports = {
         do {
           const splitName = checkNames[index];
           if (splitName.length === 1) return undefined;
-          const isPascalCase = testPascalCase(splitName);
-          const isAllowedAllCaps = allowAllCaps && testAllCaps(splitName);
           const isIgnored = ignoreCheck(ignore, splitName);
 
+          const checkName = allowLeadingUnderscore && splitName.startsWith('_') ? splitName.slice(1) : splitName;
+          const isPascalCase = testPascalCase(checkName);
+          const isAllowedAllCaps = allowAllCaps && testAllCaps(checkName);
+
           if (!isPascalCase && !isAllowedAllCaps && !isIgnored) {
             context.report({
               node,

tests/lib/rules/jsx-pascal-case.js

@@ -93,6 +93,12 @@ ruleTester.run('jsx-pascal-case', rule, {
   }, {
     code: '<Styled.h1 />',
     options: [{allowNamespace: true}]
+  }, {
+    code: '<_TEST_COMPONENT />',
+    options: [{allowAllCaps: true, allowLeadingUnderscore: true}]
+  }, {
+    code: '<_TestComponent />',
+    options: [{allowLeadingUnderscore: true}]
   }],
 
   invalid: [{
@@ -127,13 +133,34 @@ ruleTester.run('jsx-pascal-case', rule, {
       messageId: 'usePascalOrSnakeCase',
       data: {name: 'TEST_COMPONENT_'}
     }]
+  }, {
+    code: '<TEST-COMPONENT />',
+    options: [{allowAllCaps: true}],
+    errors: [{
+      messageId: 'usePascalOrSnakeCase',
+      data: {name: 'TEST-COMPONENT'}
+    }]
   }, {
     code: '<__ />',
     options: [{allowAllCaps: true}],
     errors: [{
       messageId: 'usePascalOrSnakeCase',
       data: {name: '__'}
     }]
+  }, {
+    code: '<_div />',
+    options: [{allowLeadingUnderscore: true}],
+    errors: [{
+      messageId: 'usePascalCase',
+      data: {name: '_div'}
+    }]
+  }, {
+    code: '<__ />',
+    options: [{allowAllCaps: true, allowLeadingUnderscore: true}],
+    errors: [{
+      messageId: 'usePascalOrSnakeCase',
+      data: {name: '__'}
+    }]
   }, {
     code: '<$a />',
     errors: [{