[Fix] display-name, prop-types: when checking for a capitalized name, ignore underscores entirely

Fixes #3560

Author: ljharb

CHANGELOG.md

@@ -16,7 +16,9 @@ This change log adheres to standards from [Keep a CHANGELOG](https://keepachange
 * [`no-unknown-property`]: allow `onLoad` on `source` (@ljharb)
 * [`jsx-first-prop-new-line`]: ensure autofix preserves generics in component name ([#3546][] @ljharb)
 * [`no-unknown-property`]: allow `fill` prop on `<symbol>` ([#3555][] @stefanprobst)
+* [`display-name`], [`prop-types`]: when checking for a capitalized name, ignore underscores entirely ([#3560][] @ljharb)
 
+[#3560]: https://github.com/jsx-eslint/eslint-plugin-react/issues/3560
 [#3555]: https://github.com/jsx-eslint/eslint-plugin-react/pull/3555
 [#3548]: https://github.com/jsx-eslint/eslint-plugin-react/pull/3548
 [#3546]: https://github.com/jsx-eslint/eslint-plugin-react/issues/3546

lib/util/isFirstLetterCapitalized.js

@@ -6,10 +6,10 @@
  * @returns {Boolean} True if first letter is capitalized.
  */
 function isFirstLetterCapitalized(word) {
-  if (!word || word.charAt(0) === '_') {
+  if (!word) {
     return false;
   }
-  const firstLetter = word.charAt(0);
+  const firstLetter = word.replace(/^_+/, '').charAt(0);
   return firstLetter.toUpperCase() === firstLetter;
 }
 

tests/lib/rules/prop-types.js

@@ -8199,6 +8199,55 @@ ruleTester.run('prop-types', rule, {
           data: { name: 'foo' },
         },
       ],
+    },
+    {
+      code: `
+        function _EventsList({ prop_ }) {
+            return (
+                <div>
+                    {prop_.events.map((event) => (
+                        <Event key={event.id} eventId={event.id} />
+                    ))}
+                </div>
+            );
+        }
+
+        function $EventsList({ prop$ }) {
+          return (
+              <div>
+                  {prop$.events.map((event) => (
+                      <Event key={event.id} eventId={event.id} />
+                  ))}
+              </div>
+          );
+      }
+      `,
+      errors: [
+        {
+          messageId: 'missingPropType',
+          data: { name: 'prop_' },
+        },
+        {
+          messageId: 'missingPropType',
+          data: { name: 'prop_.events' },
+        },
+        {
+          messageId: 'missingPropType',
+          data: { name: 'prop_.events.map' },
+        },
+        {
+          messageId: 'missingPropType',
+          data: { name: 'prop$' },
+        },
+        {
+          messageId: 'missingPropType',
+          data: { name: 'prop$.events' },
+        },
+        {
+          messageId: 'missingPropType',
+          data: { name: 'prop$.events.map' },
+        },
+      ],
     }
   )),
 });

tests/util/isFirstLetterCapitalized.js

@@ -15,11 +15,15 @@ describe('isFirstLetterCapitalized', () => {
     assert.equal(isFirstLetterCapitalized('isCapitalized'), false);
     assert.equal(isFirstLetterCapitalized('lowercase'), false);
     assert.equal(isFirstLetterCapitalized('_startsWithUnderscore'), false);
-    assert.equal(isFirstLetterCapitalized('_StartsWithUnderscore'), false);
+    assert.equal(isFirstLetterCapitalized('__startsWithUnderscore'), false);
   });
 
-  it('should return true for capitalized string', () => {
+  it('should return true for capitalized string, with or without leading underscores', () => {
     assert.equal(isFirstLetterCapitalized('IsCapitalized'), true);
+    assert.equal(isFirstLetterCapitalized('_IsCapitalized'), true);
+    assert.equal(isFirstLetterCapitalized('__IsCapitalized'), true);
     assert.equal(isFirstLetterCapitalized('UPPERCASE'), true);
+    assert.equal(isFirstLetterCapitalized('_UPPERCASE'), true);
+    assert.equal(isFirstLetterCapitalized('__UPPERCASE'), true);
   });
 });