feat: lint rule for camelCase file names

Author: mattzcarey

eslint-rules/fileNaming.mjs

@@ -0,0 +1,107 @@
+// @ts-check
+
+/**
+ * Custom ESLint rule to enforce camelCase file naming convention.
+ * @type {import('eslint').Rule.RuleModule}
+ */
+export const fileNamingRule = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'Enforce camelCase file naming convention',
+      recommended: true,
+    },
+    messages: {
+      invalidFileName:
+        "File name '{{fileName}}' should be camelCase. Suggested: '{{suggested}}'",
+    },
+    schema: [
+      {
+        type: 'object',
+        properties: {
+          ignore: {
+            type: 'array',
+            items: { type: 'string' },
+            description: 'Regex patterns for file names to ignore',
+          },
+        },
+        additionalProperties: false,
+      },
+    ],
+  },
+
+  create(context) {
+    return {
+      Program(node) {
+        const filename = context.filename || context.getFilename();
+        const options = context.options[0] || {};
+        const ignorePatterns = (options.ignore || []).map(
+          (/** @type {string} */ pattern) => new RegExp(pattern)
+        );
+
+        // Extract just the file name from the full path
+        const parts = filename.split('/');
+        const fileName = parts[parts.length - 1];
+
+        // Skip non-TypeScript files
+        if (!fileName.endsWith('.ts') && !fileName.endsWith('.tsx')) {
+          return;
+        }
+
+        // Check if file matches any ignore pattern
+        for (const pattern of ignorePatterns) {
+          if (pattern.test(fileName)) {
+            return;
+          }
+        }
+
+        // Get the base name (without extension)
+        // Handle test files: name.test.ts -> name
+        const baseName = fileName
+          .replace(/\.test\.ts$/, '')
+          .replace(/\.spec\.ts$/, '')
+          .replace(/\.test\.tsx$/, '')
+          .replace(/\.spec\.tsx$/, '')
+          .replace(/\.ts$/, '')
+          .replace(/\.tsx$/, '');
+
+        // Get the extension for suggestion
+        const extension = fileName.slice(baseName.length);
+
+        // Check if the base name follows camelCase
+        // camelCase: starts with lowercase letter, then letters/numbers only
+        const camelCaseRegex = /^[a-z][a-zA-Z0-9]*$/;
+
+        if (!camelCaseRegex.test(baseName)) {
+          const suggested = toCamelCase(baseName) + extension;
+
+          context.report({
+            node,
+            messageId: 'invalidFileName',
+            data: {
+              fileName,
+              suggested,
+            },
+          });
+        }
+      },
+    };
+  },
+};
+
+/**
+ * Convert a string to camelCase
+ * @param {string} str
+ * @returns {string}
+ */
+function toCamelCase(str) {
+  return str
+    .split(/[-_.\s]+/)
+    .map((word, index) => {
+      if (index === 0) {
+        return word.toLowerCase();
+      }
+      return word.charAt(0).toUpperCase() + word.slice(1).toLowerCase();
+    })
+    .join('');
+}

eslint.config.mjs

@@ -4,6 +4,14 @@ import eslint from '@eslint/js';
 import tseslint from 'typescript-eslint';
 import eslintConfigPrettier from 'eslint-config-prettier/flat';
 import nodePlugin from 'eslint-plugin-n';
+import { fileNamingRule } from './eslint-rules/fileNaming.mjs';
+
+// Local plugin for custom rules
+const localPlugin = {
+    rules: {
+        'file-naming': fileNamingRule,
+    },
+};
 
 export default tseslint.config(
     eslint.configs.recommended,
@@ -13,11 +21,18 @@ export default tseslint.config(
             reportUnusedDisableDirectives: false
         },
         plugins: {
-            n: nodePlugin
+            n: nodePlugin,
+            local: localPlugin
         },
         rules: {
             '@typescript-eslint/no-unused-vars': ['error', { argsIgnorePattern: '^_' }],
-            'n/prefer-node-protocol': 'error'
+            'n/prefer-node-protocol': 'error',
+            'local/file-naming': ['warn', {
+                ignore: [
+                    '^spec\\.types',
+                    '^types\\.'
+                ]
+            }]
         }
     },
     {