npm install fails: TypeScript errors due to ESLint Linter.Config languageOptions index-signature typing (TS4111/TS2698/TS18046)

[apple-yagi]

What happened

Running npm install fails because prepare runs npm run build && husky, and tsc errors out.

Steps to reproduce

1. Clone this repo
2. npm install

Actual result

lib/config.ts:56:57 - error TS4111: Property 'ecmaVersion' comes from an index signature, so it must be accessed with ['ecmaVersion'].

56    ecmaVersion: configXoTypescript[0]?.languageOptions?.ecmaVersion,
                                                           ~~~~~~~~~~~

lib/config.ts:57:56 - error TS4111: Property 'sourceType' comes from an index signature, so it must be accessed with ['sourceType'].

57    sourceType: configXoTypescript[0]?.languageOptions?.sourceType,
                                                          ~~~~~~~~~~

lib/config.ts:59:5 - error TS2698: Spread types may only be created from object types.

59     ...configXoTypescript[0]?.languageOptions?.parserOptions,
       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

lib/config.ts:59:48 - error TS4111: Property 'parserOptions' comes from an index signature, so it must be accessed with ['parserOptions'].

59     ...configXoTypescript[0]?.languageOptions?.parserOptions,
                                                  ~~~~~~~~~~~~~

lib/config.ts:384:5 - error TS2698: Spread types may only be created from object types.

384     ...configXoTypescript[4]?.languageOptions?.parserOptions,
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

lib/config.ts:384:48 - error TS4111: Property 'parserOptions' comes from an index signature, so it must be accessed with ['parserOptions'].

384     ...configXoTypescript[4]?.languageOptions?.parserOptions,
                                                   ~~~~~~~~~~~~~

lib/utils.ts:92:32 - error TS4111: Property 'parser' comes from an index signature, so it must be accessed with ['parser'].

92    && !config.languageOptions?.parser
                                  ~~~~~~

lib/utils.ts:93:8 - error TS7053: Element implicitly has an 'any' type because expression of type '"project"' can't be used to index type '{}'.
  Property 'project' does not exist on type '{}'.

93    && !config.languageOptions?.parserOptions?.['project']
          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

lib/utils.ts:93:32 - error TS4111: Property 'parserOptions' comes from an index signature, so it must be accessed with ['parserOptions'].

93    && !config.languageOptions?.parserOptions?.['project']
                                  ~~~~~~~~~~~~~

lib/utils.ts:132:29 - error TS4111: Property 'parser' comes from an index signature, so it must be accessed with ['parser'].

132      config.languageOptions.parser = configXoTypescript[1]?.languageOptions?.parser;
                                ~~~~~~

lib/utils.ts:132:78 - error TS4111: Property 'parser' comes from an index signature, so it must be accessed with ['parser'].

132      config.languageOptions.parser = configXoTypescript[1]?.languageOptions?.parser;
                                                                                 ~~~~~~

lib/utils.ts:142:4 - error TS7053: Element implicitly has an 'any' type because expression of type '"project"' can't be used to index type '{}'.
  Property 'project' does not exist on type '{}'.

142    config.languageOptions?.parserOptions?.['project'] !== undefined
       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

lib/utils.ts:142:28 - error TS4111: Property 'parserOptions' comes from an index signature, so it must be accessed with ['parserOptions'].

142    config.languageOptions?.parserOptions?.['project'] !== undefined
                               ~~~~~~~~~~~~~

lib/utils.ts:143:7 - error TS7053: Element implicitly has an 'any' type because expression of type '"projectService"' can't be used to index type '{}'.
  Property 'projectService' does not exist on type '{}'.

143    || config.languageOptions?.parserOptions?.['projectService'] !== undefined
          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

lib/utils.ts:143:31 - error TS4111: Property 'parserOptions' comes from an index signature, so it must be accessed with ['parserOptions'].

143    || config.languageOptions?.parserOptions?.['projectService'] !== undefined
                                  ~~~~~~~~~~~~~

lib/utils.ts:144:7 - error TS7053: Element implicitly has an 'any' type because expression of type '"tsconfigRootDir"' can't be used to index type '{}'.
  Property 'tsconfigRootDir' does not exist on type '{}'.

144    || config.languageOptions?.parserOptions?.['tsconfigRootDir'] !== undefined
          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

lib/utils.ts:144:31 - error TS4111: Property 'parserOptions' comes from an index signature, so it must be accessed with ['parserOptions'].

144    || config.languageOptions?.parserOptions?.['tsconfigRootDir'] !== undefined
                                  ~~~~~~~~~~~~~

lib/xo.ts:287:26 - error TS4111: Property 'parserOptions' comes from an index signature, so it must be accessed with ['parserOptions'].

287   config.languageOptions.parserOptions ??= {};
                             ~~~~~~~~~~~~~

lib/xo.ts:288:3 - error TS18046: 'config.languageOptions.parserOptions' is of type 'unknown'.

288   config.languageOptions.parserOptions['projectService'] = false;
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

lib/xo.ts:288:26 - error TS4111: Property 'parserOptions' comes from an index signature, so it must be accessed with ['parserOptions'].

288   config.languageOptions.parserOptions['projectService'] = false;
                             ~~~~~~~~~~~~~

lib/xo.ts:289:3 - error TS18046: 'config.languageOptions.parserOptions' is of type 'unknown'.

289   config.languageOptions.parserOptions['project'] = fallbackTsConfigPath;
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

lib/xo.ts:289:26 - error TS4111: Property 'parserOptions' comes from an index signature, so it must be accessed with ['parserOptions'].

289   config.languageOptions.parserOptions['project'] = fallbackTsConfigPath;
                             ~~~~~~~~~~~~~

lib/xo.ts:290:3 - error TS18046: 'config.languageOptions.parserOptions' is of type 'unknown'.

290   config.languageOptions.parserOptions['tsconfigRootDir'] = this.linterOptions.cwd;
      ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

lib/xo.ts:290:26 - error TS4111: Property 'parserOptions' comes from an index signature, so it must be accessed with ['parserOptions'].

290   config.languageOptions.parserOptions['tsconfigRootDir'] = this.linterOptions.cwd;
                             ~~~~~~~~~~~~~

test/xo/files-matching.test.ts:494:5 - error TS2578: Unused '@ts-expect-error' directive.

494     // @ts-expect-error - This is a test, parserOptions.project just needs to be set
        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Found 25 errors in 4 files.

Errors  Files
     6  lib/config.ts:56
    11  lib/utils.ts:92
     7  lib/xo.ts:287
     1  test/xo/files-matching.test.ts:494

Expected result

npm install completes successfully.

Notes / suspicion

Looks like eslint’s Linter.Config.languageOptions is typed via an index signature (or unknown)
in the current ESLint type definitions, and @sindresorhus/tsconfig enables
noPropertyAccessFromIndexSignature, so dot access/spread is now rejected.