feat: improved errors when config can not be found

src/cli.ts

@@ -2,6 +2,8 @@ import process from 'node:process'
 import fs from 'node:fs/promises'
 import { existsSync } from 'node:fs'
 import { relative, resolve } from 'node:path'
+import { types } from 'node:util'
+
 import open from 'open'
 import { getPort } from 'get-port-please'
 import cac from 'cac'
@@ -40,6 +42,11 @@ cli
       globMatchedFiles: options.files,
     })
 
+    if (types.isNativeError(configs)) {
+      configs.prettyPrint()
+      process.exit(1)
+    }
+
     let baseURL = options.base
     if (!baseURL.endsWith('/'))
       baseURL += '/'

src/configs.ts

@@ -1,5 +1,6 @@
-import { dirname, relative, resolve } from 'node:path'
+import { basename, dirname, relative, resolve } from 'node:path'
 import process from 'node:process'
+import { types } from 'node:util'
 import { ConfigArray } from '@eslint/config-array'
 import { configArrayFindFiles } from '@voxpelli/config-array-find-files'
 import { bundleRequire } from 'bundle-require'
@@ -8,7 +9,7 @@ import c from 'picocolors'
 import { resolve as resolveModule } from 'mlly'
 import type { FlatConfigItem, MatchedFile, Payload, RuleInfo } from '../shared/types'
 import { isIgnoreOnlyConfig, matchFile } from '../shared/configs'
-import { MARK_CHECK, MARK_INFO, configFilenames } from './constants'
+import { MARK_CHECK, MARK_ERROR, MARK_INFO, configFilenames, legacyConfigFilenames } from './constants'
 
 export interface ReadConfigOptions extends ResolveConfigPathOptions {
   /**
@@ -40,6 +41,47 @@ export interface ResolveConfigPathOptions {
   userBasePath?: string
 }
 
+export class ConfigPathError extends Error {
+  override name = 'ConfigPathError' as const
+
+  constructor(
+    public basePath: string,
+    public configFilenames: string[],
+  ) {
+    super('Cannot find ESLint config file')
+  }
+
+  prettyPrint() {
+    console.error(MARK_ERROR, this.message, c.dim(`
+
+Looked in ${c.underline(this.basePath)} and parent folders for:
+
+ * ${this.configFilenames.join('\n * ')}`,
+    ))
+  }
+}
+
+export class ConfigPathLegacyError extends Error {
+  override name = 'ConfigPathLegacyError' as const
+
+  constructor(
+    public basePath: string,
+    public configFilename: string,
+  ) {
+    super('Found ESLint legacy config file')
+  }
+
+  prettyPrint() {
+    console.error(MARK_ERROR, this.message, c.dim(`
+
+Encountered unsupported legacy config ${c.underline(this.configFilename)} in ${c.underline(this.basePath)}
+
+\`@eslint/config-inspector\` only works with the new flat config format:
+https://eslint.org/docs/latest/use/configure/configuration-files-new`,
+    ))
+  }
+}
+
 /**
  * Search and read the ESLint config file.
  *
@@ -55,12 +97,27 @@ export async function resolveConfigPath(options: ResolveConfigPathOptions) {
   if (userBasePath)
     userBasePath = resolve(cwd, userBasePath)
 
-  const configPath = userConfigPath
-    ? resolve(cwd, userConfigPath)
-    : await findUp(configFilenames, { cwd: userBasePath || cwd })
+  const lookupBasePath = userBasePath || cwd
+
+  let configPath = userConfigPath && resolve(cwd, userConfigPath)
+
+  if (!configPath) {
+    configPath = await findUp(configFilenames, { cwd: lookupBasePath })
+  }
+
+  if (!configPath) {
+    const legacyConfigPath = await findUp(legacyConfigFilenames, { cwd: lookupBasePath })
 
-  if (!configPath)
-    throw new Error('Cannot find ESLint config file')
+    return legacyConfigPath
+      ? new ConfigPathLegacyError(
+        `${relative(cwd, dirname(legacyConfigPath))}/`,
+        basename(legacyConfigPath),
+      )
+      : new ConfigPathError(
+        `${relative(cwd, lookupBasePath)}/`,
+        configFilenames,
+      )
+  }
 
   const basePath = userBasePath || (
     userConfigPath
@@ -83,13 +140,19 @@ export async function resolveConfigPath(options: ResolveConfigPathOptions) {
  */
 export async function readConfig(
   options: ReadConfigOptions,
-): Promise<{ configs: FlatConfigItem[], payload: Payload, dependencies: string[] }> {
+): Promise<ConfigPathLegacyError | ConfigPathError | { configs: FlatConfigItem[], payload: Payload, dependencies: string[] }> {
   const {
     chdir = true,
     globMatchedFiles: globFiles = true,
   } = options
 
-  const { basePath, configPath } = await resolveConfigPath(options)
+  const resolvedConfigPath = await resolveConfigPath(options)
+
+  if (types.isNativeError(resolvedConfigPath)) {
+    return resolvedConfigPath
+  }
+
+  const { basePath, configPath } = resolvedConfigPath
   if (chdir && basePath !== process.cwd())
     process.chdir(basePath)
 

src/constants.ts

@@ -9,5 +9,14 @@ export const configFilenames = [
   'eslint.config.cts',
 ]
 
+export const legacyConfigFilenames = [
+  '.eslintrc.js',
+  '.eslintrc.cjs',
+  '.eslintrc.yaml',
+  '.eslintrc.yml',
+  '.eslintrc.json',
+]
+
 export const MARK_CHECK = c.green('✔')
 export const MARK_INFO = c.blue('ℹ')
+export const MARK_ERROR = c.red('✖')

src/ws.ts

@@ -1,3 +1,6 @@
+import process from 'node:process'
+import { types } from 'node:util'
+
 import chokidar from 'chokidar'
 import type { WebSocket } from 'ws'
 import { WebSocketServer } from 'ws'
@@ -27,7 +30,15 @@ export async function createWsServer(options: CreateWsServerOptions) {
     ws.on('close', () => wsClients.delete(ws))
   })
 
-  const { basePath } = await resolveConfigPath(options)
+  const resolvedConfigPath = await resolveConfigPath(options)
+
+  if (types.isNativeError(resolvedConfigPath)) {
+    resolvedConfigPath.prettyPrint()
+    process.exit(1)
+  }
+
+  const { basePath } = resolvedConfigPath
+
   const watcher = chokidar.watch([], {
     ignoreInitial: true,
     cwd: basePath,
@@ -51,6 +62,9 @@ export async function createWsServer(options: CreateWsServerOptions) {
       if (!payload) {
         return await readConfig(options)
           .then((res) => {
+            if (types.isNativeError(res)) {
+              throw res
+            }
             const _payload = payload = res.payload
             _payload.meta.wsPort = port
             watcher.add(res.dependencies)