`prefer-immutable-types` crashes on Next.js `GetStaticPropsContext` type

[builtbyjavi]

Why the issue was filed?

Running ESLint with eslint-plugin-functional's rule functional/prefer-immutable-types on a Next.js page crashes ESLint with "ErrorType encountered." when the rule analyzes a parameter typed with Next's GetStaticPropsContext<T>. This occurs only in type-aware mode (parserOptions.project set); locally without type-aware linting on pages it does not crash, but in CI it does.

Expected behavior

The rule should not crash when encountering TypeScript's internal ErrorType during type analysis. It should safely treat unknown/unresolvable types as "Unknown" or skip and either report no violation or a normal diagnostic, without throwing.

Actual behavior

ESLint process exits with an error when linting the file:

ESLint: 8.56.0

Error: ErrorType encountered.
Occurred while linting /home/runner/_work/agora/agora/src/pages/dummyPage.tsx:8
Rule: "functional/prefer-immutable-types"
    at getTypeData (/home/runner/_work/agora/agora/node_modules/is-immutable-type/dist/index.cjs:118:15)
    at Object.getTypeImmutability (/home/runner/_work/agora/agora/node_modules/is-immutable-type/dist/index.cjs:378:22)
    at getTypeImmutabilityOfNode (/home/runner/_work/agora/agora/node_modules/eslint-plugin-functional/lib/classic.cjs:850:28)
    at /home/runner/_work/agora/agora/node_modules/eslint-plugin-functional/lib/classic.cjs:2774:30
    at Array.map (<anonymous>)
    at getParameterTypeViolations (/home/runner/_work/agora/agora/node_modules/eslint-plugin-functional/lib/classic.cjs:2739:10)
    at checkFunction$1 (/home/runner/_work/agora/agora/node_modules/eslint-plugin-functional/lib/classic.cjs:2891:12)

The crash occurs when the rule analyzes a function parameter typed with GetStaticPropsContext<PageParams>.

Steps to reproduce

Environment:

• Node: 22
• TypeScript: 5.7.2
• ESLint: 8.56.0
• @typescript-eslint/parser: 5.62.0
• eslint-plugin-functional: 6.6.0
• next: 12.3.4

ESLint config (from .eslintrc.js):

{
  settings: {
    parser: '@typescript-eslint/parser',
    parserOptions: {
      project: './tsconfig.json',
    },
  },
  rules: {
    'functional/prefer-immutable-types': [
      'error',
      {
        enforcement: 'ReadonlyShallow',
        ignoreInferredTypes: true,
        variables: {
          enforcement: 'None',
        },
        fixer: {
          ReadonlyShallow: [
            {
              pattern: '^([_$a-zA-Z\\xA0-\\uFFFF][_$a-zA-Z0-9\\xA0-\\uFFFF]*\\[\\])$',
              replace: 'readonly $1',
            },
            {
              pattern: '^(Array|Map|Set)<(.+)>$',
              replace: 'Readonly$1<$2>',
            },
            {
              pattern: '^(.+)$',
              replace: 'Readonly<$1>',
            },
          ],
        },
      },
    ],
  },
}

Note: wrapping the type with Readonly<> has no effect on the crash.
Minimal reproduction file:

import type { GetStaticPropsContext } from 'next';

type PageParams = {
  gameId: string;
  tournamentId: string;
};

export async function getStaticProps(
  props: GetStaticPropsContext<PageParams>
) {
  const { gameId, tournamentId } = props.params!;
  return { props: {} as const };
}

Run:

npx eslint --max-warnings=0 src/pages/dummyPage.tsx

[shaffy9633]

ran into the same thing!!