Improve "class-name-casing" to accept an options object with an "allo…

…wUnderscorePrefix" feature
typescript-eslint · Aug 3, 2019 · a58c9a8 · a58c9a8
1 parent 3351e8e
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diff --git a/packages/eslint-plugin/docs/rules/class-name-casing.md b/packages/eslint-plugin/docs/rules/class-name-casing.md
@@ -5,6 +5,17 @@ This rule enforces PascalCased names for classes and interfaces.
 ## Rule Details
 
 This rule aims to make it easy to differentiate classes from regular variables at a glance.
+The `_` prefix is sometimes used to designate a private declaration, so the rule also supports a name
+that might be `_Example` instead of `Example`.
+
+## Options
+
+This rule has an object option:
+
+- `"allowUnderscorePrefix": false`: (default) does not allow the name to have an underscore prefix
+- `"allowUnderscorePrefix": true`: allows the name to optionally have an underscore prefix
+
+## Examples
 
 Examples of **incorrect** code for this rule:
 
@@ -16,6 +27,8 @@ class Another_Invalid_Class_Name {}
 var bar = class invalidName {};
 
 interface someInterface {}
+
+class _InternalClass {}
 ```
 
 Examples of **correct** code for this rule:
@@ -28,6 +41,9 @@ export default class {}
 var foo = class {};
 
 interface SomeInterface {}
+
+/* eslint @typescript-eslint/class-name-casing: { "allowUnderscorePrefix": true } */
+class _InternalClass {}
 ```
 
 ## When Not To Use It

diff --git a/packages/eslint-plugin/src/rules/class-name-casing.ts b/packages/eslint-plugin/src/rules/class-name-casing.ts
@@ -4,7 +4,14 @@ import {
 } from '@typescript-eslint/experimental-utils';
 import * as util from '../util';
 
-export default util.createRule({
+type Options = [
+  {
+    allowUnderscorePrefix?: boolean;
+  },
+];
+type MessageIds = 'notPascalCased';
+
+export default util.createRule<Options, MessageIds>({
   name: 'class-name-casing',
   meta: {
     type: 'suggestion',
@@ -16,16 +23,31 @@ export default util.createRule({
     messages: {
       notPascalCased: "{{friendlyName}} '{{name}}' must be PascalCased.",
     },
-    schema: [],
+    schema: [
+      {
+        type: 'object',
+        properties: {
+          allowUnderscorePrefix: {
+            type: 'boolean',
+            default: false,
+          },
+        },
+        additionalProperties: false,
+      },
+    ],
   },
-  defaultOptions: [],
-  create(context) {
+  defaultOptions: [{ allowUnderscorePrefix: false }],
+  create(context, [options]) {
     /**
      * Determine if the identifier name is PascalCased
      * @param name The identifier name
      */
     function isPascalCase(name: string): boolean {
-      return /^[A-Z][0-9A-Za-z]*$/.test(name);
+      if (options.allowUnderscorePrefix) {
+        return /^_?[A-Z][0-9A-Za-z]*$/.test(name);
+      } else {
+        return /^[A-Z][0-9A-Za-z]*$/.test(name);
+      }
     }
 
     /**

diff --git a/packages/eslint-plugin/tests/rules/class-name-casing.test.ts b/packages/eslint-plugin/tests/rules/class-name-casing.test.ts
@@ -14,6 +14,10 @@ ruleTester.run('class-name-casing', rule, {
         sourceType: 'module',
       },
     },
+    {
+      code: 'class _NameWithUnderscore {}',
+      options: [{ allowUnderscorePrefix: true }],
+    },
     'var Foo = class {};',
     'interface SomeInterface {}',
     'class ClassNameWithDigit2 {}',
@@ -50,6 +54,20 @@ ruleTester.run('class-name-casing', rule, {
         },
       ],
     },
+    {
+      code: 'class _NameWithUnderscore {}',
+      errors: [
+        {
+          messageId: 'notPascalCased',
+          data: {
+            friendlyName: 'Class',
+            name: '_NameWithUnderscore',
+          },
+          line: 1,
+          column: 7,
+        },
+      ],
+    },
     {
       code: 'var foo = class {};',
       errors: [