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fix(typescript-eslint): gracefully handle invalid flat config objects in config helper #11070

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Apr 21, 2025
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fix(typescript-eslint): gracefully handle invalid flat config objects in config helper #11070

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173 changes: 113 additions & 60 deletions packages/typescript-eslint/src/config-helper.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -92,70 +92,123 @@ export type ConfigArray = TSESLint.FlatConfig.ConfigArray;
export function config(
...configs: InfiniteDepthConfigWithExtends[]
): ConfigArray {
const flattened =
// @ts-expect-error -- intentionally an infinite type
configs.flat(Infinity) as ConfigWithExtends[];
return flattened.flatMap((configWithExtends, configIndex) => {
const { extends: extendsArr, ...config } = configWithExtends;
if (extendsArr == null || extendsArr.length === 0) {
return config;
}
const extendsArrFlattened = extendsArr.flat(
Infinity,
) as ConfigWithExtends[];

const undefinedExtensions = extendsArrFlattened.reduce<number[]>(
(acc, extension, extensionIndex) => {
const maybeExtension = extension as
| TSESLint.FlatConfig.Config
| undefined;
if (maybeExtension == null) {
acc.push(extensionIndex);
return configImpl(...configs);
}

// Implementation of the config function without assuming the runtime type of
// the input.
function configImpl(...configs: unknown[]): ConfigArray {
const flattened = configs.flat(Infinity);
return flattened.flatMap(
(
configWithExtends,
configIndex,
): TSESLint.FlatConfig.Config | TSESLint.FlatConfig.Config[] => {
if (
configWithExtends == null ||
typeof configWithExtends !== 'object' ||
!('extends' in configWithExtends)
) {
// Unless the object is a config object with extends key, just forward it
// along to eslint.
return configWithExtends as TSESLint.FlatConfig.Config;
}

const { extends: extendsArr, ..._config } = configWithExtends;
const config = _config as {
name?: unknown;
extends?: unknown;
files?: unknown;
ignores?: unknown;
};

if (extendsArr == null) {
// If the extends value is nullish, just forward along the rest of the
// config object to eslint.
return config as TSESLint.FlatConfig.Config;
}

const name = ((): string | undefined => {
if ('name' in configWithExtends && configWithExtends.name != null) {
if (typeof configWithExtends.name !== 'string') {
throw new Error(
`tseslint.config(): Config at index ${configIndex} has a 'name' property that is not a string.`,
);
}
return configWithExtends.name;
}
return acc;
},
[],
);
if (undefinedExtensions.length) {
const configName =
configWithExtends.name != null
? `, named "${configWithExtends.name}",`
: ' (anonymous)';
const extensionIndices = undefinedExtensions.join(', ');
throw new Error(
`Your config at index ${configIndex}${configName} contains undefined` +
` extensions at the following indices: ${extensionIndices}.`,
);
}

const configArray = [];

for (const extension of extendsArrFlattened) {
const name = [config.name, extension.name].filter(Boolean).join('__');
if (isPossiblyGlobalIgnores(extension)) {
// If it's a global ignores, then just pass it along
configArray.push({
...extension,
...(name && { name }),
});
} else {
configArray.push({
...extension,
...(config.files && { files: config.files }),
...(config.ignores && { ignores: config.ignores }),
...(name && { name }),
});
return undefined;
})();
const nameErrorPhrase =
name != null ? `, named "${name}",` : ' (anonymous)';

if (!Array.isArray(extendsArr)) {
throw new TypeError(
`tseslint.config(): Config at index ${configIndex}${nameErrorPhrase} has an 'extends' property that is not an array.`,
);
}
}

// If the base config could form a global ignores object, then we mustn't include
// it in the output. Otherwise, we must add it in order for it to have effect.
if (!isPossiblyGlobalIgnores(config)) {
configArray.push(config);
}
const extendsArrFlattened = (extendsArr as unknown[]).flat(Infinity);

const nonObjectExtensions = [];
for (const [extensionIndex, extension] of extendsArrFlattened.entries()) {
// special error message to be clear we don't support eslint's stringly typed extends.
// https://eslint.org/docs/latest/use/configure/configuration-files#extending-configurations
if (typeof extension === 'string') {
throw new Error(
`tseslint.config(): Config at index ${configIndex}${nameErrorPhrase} has an 'extends' array that contains a string (${JSON.stringify(extension)}) at index ${extensionIndex}.` +
" This is a feature of eslint's `defineConfig()` helper and is not supported by typescript-eslint." +
' Please provide a config object instead.',
);
}
if (extension == null || typeof extension !== 'object') {
nonObjectExtensions.push(extensionIndex);
}
}
if (nonObjectExtensions.length > 0) {
const extensionIndices = nonObjectExtensions.join(', ');
throw new Error(
`tseslint.config(): Config at index ${configIndex}${nameErrorPhrase} contains non-object` +
` extensions at the following indices: ${extensionIndices}.`,
);
}

const configArray = [];

for (const _extension of extendsArrFlattened) {
const extension = _extension as {
name?: unknown;
files?: unknown;
ignores?: unknown;
};
const resolvedConfigName = [name, extension.name]
.filter(Boolean)
.join('__');
if (isPossiblyGlobalIgnores(extension)) {
// If it's a global ignores, then just pass it along
configArray.push({
...extension,
...(resolvedConfigName !== '' ? { name: resolvedConfigName } : {}),
});
} else {
configArray.push({
...extension,
...(config.files ? { files: config.files } : {}),
...(config.ignores ? { ignores: config.ignores } : {}),
...(resolvedConfigName !== '' ? { name: resolvedConfigName } : {}),
});
}
}

// If the base config could form a global ignores object, then we mustn't include
// it in the output. Otherwise, we must add it in order for it to have effect.
if (!isPossiblyGlobalIgnores(config)) {
configArray.push(config);
}

return configArray;
});
return configArray as ConfigArray;
},
);
}

/**
Expand Down
92 changes: 75 additions & 17 deletions packages/typescript-eslint/tests/config-helper.test.ts
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Open in desktop
Original file line number Diff line number Diff line change
@@ -1,11 +1,11 @@
import type { TSESLint } from '@typescript-eslint/utils';

import plugin from '../src/index';
import tseslint from '../src/index';

describe('config helper', () => {
it('works without extends', () => {
expect(
plugin.config({
tseslint.config({
files: ['file'],
ignores: ['ignored'],
rules: { rule: 'error' },
Expand All @@ -21,7 +21,7 @@ describe('config helper', () => {

it('flattens extended configs', () => {
expect(
plugin.config({
tseslint.config({
extends: [{ rules: { rule1: 'error' } }, { rules: { rule2: 'error' } }],
rules: { rule: 'error' },
}),
Expand All @@ -34,7 +34,7 @@ describe('config helper', () => {

it('flattens extended configs with files and ignores', () => {
expect(
plugin.config({
tseslint.config({
extends: [{ rules: { rule1: 'error' } }, { rules: { rule2: 'error' } }],
files: ['common-file'],
ignores: ['common-ignored'],
Expand Down Expand Up @@ -63,7 +63,7 @@ describe('config helper', () => {
const extension: TSESLint.FlatConfig.Config = { rules: { rule1: 'error' } };

expect(() =>
plugin.config(
tseslint.config(
{
extends: [extension],
files: ['common-file'],
Expand All @@ -81,7 +81,7 @@ describe('config helper', () => {
},
),
).toThrow(
'Your config at index 1, named "my-config-2", contains undefined ' +
'tseslint.config(): Config at index 1, named "my-config-2", contains non-object ' +
'extensions at the following indices: 0, 2',
);
});
Expand All @@ -90,7 +90,7 @@ describe('config helper', () => {
const extension: TSESLint.FlatConfig.Config = { rules: { rule1: 'error' } };

expect(() =>
plugin.config(
tseslint.config(
{
extends: [extension],
files: ['common-file'],
Expand All @@ -107,14 +107,14 @@ describe('config helper', () => {
},
),
).toThrow(
'Your config at index 1 (anonymous) contains undefined extensions at ' +
'tseslint.config(): Config at index 1 (anonymous) contains non-object extensions at ' +
'the following indices: 0, 2',
);
});

it('flattens extended configs with config name', () => {
expect(
plugin.config({
tseslint.config({
extends: [{ rules: { rule1: 'error' } }, { rules: { rule2: 'error' } }],
files: ['common-file'],
ignores: ['common-ignored'],
Expand Down Expand Up @@ -145,7 +145,7 @@ describe('config helper', () => {

it('flattens extended configs with names if base config is unnamed', () => {
expect(
plugin.config({
tseslint.config({
extends: [
{ name: 'extension-1', rules: { rule1: 'error' } },
{ rules: { rule2: 'error' } },
Expand Down Expand Up @@ -176,7 +176,7 @@ describe('config helper', () => {

it('merges config items names', () => {
expect(
plugin.config({
tseslint.config({
extends: [
{ name: 'extension-1', rules: { rule1: 'error' } },
{ rules: { rule2: 'error' } },
Expand Down Expand Up @@ -210,7 +210,7 @@ describe('config helper', () => {

it('allows nested arrays in the config function', () => {
expect(
plugin.config(
tseslint.config(
{ rules: { rule1: 'error' } },
[{ rules: { rule2: 'error' } }],
[[{ rules: { rule3: 'error' } }]],
Expand All @@ -228,7 +228,7 @@ describe('config helper', () => {

it('allows nested arrays in extends', () => {
expect(
plugin.config({
tseslint.config({
extends: [
{ rules: { rule1: 'error' } },
[{ rules: { rule2: 'error' } }],
Expand All @@ -249,7 +249,7 @@ describe('config helper', () => {
});

it('does not create global ignores in extends', () => {
const configWithIgnores = plugin.config({
const configWithIgnores = tseslint.config({
extends: [{ rules: { rule1: 'error' } }, { rules: { rule2: 'error' } }],
ignores: ['ignored'],
});
Expand All @@ -265,7 +265,7 @@ describe('config helper', () => {
});

it('creates noop config in extends', () => {
const configWithMetadata = plugin.config({
const configWithMetadata = tseslint.config({
extends: [{ rules: { rule1: 'error' } }, { rules: { rule2: 'error' } }],
files: ['file'],
ignores: ['ignored'],
Expand Down Expand Up @@ -297,7 +297,7 @@ describe('config helper', () => {

it('does not create global ignores when extending empty configs', () => {
expect(
plugin.config({
tseslint.config({
extends: [{ rules: { rule1: 'error' } }, {}],
ignores: ['ignored'],
}),
Expand All @@ -310,10 +310,68 @@ describe('config helper', () => {

it('handles name field when global-ignoring in extension', () => {
expect(
plugin.config({
tseslint.config({
extends: [{ ignores: ['files/**/*'], name: 'global-ignore-stuff' }],
ignores: ['ignored'],
}),
).toEqual([{ ignores: ['files/**/*'], name: 'global-ignore-stuff' }]);
});

it('throws error when extends is not an array', () => {
expect(() =>
tseslint.config({
// @ts-expect-error purposely testing invalid values
extends: 42,
}),
).toThrow(
"tseslint.config(): Config at index 0 (anonymous) has an 'extends' property that is not an array.",
);
});

it.each([undefined, null, 'not a config object', 42])(
'passes invalid arguments through unchanged',
config => {
expect(
tseslint.config(
// @ts-expect-error purposely testing invalid values
config,
),
).toStrictEqual([config]);
},
);

it('gives a special error message for string extends', () => {
expect(() =>
tseslint.config({
// @ts-expect-error purposely testing invalid values
extends: ['some-string'],
}),
).toThrow(
'tseslint.config(): Config at index 0 (anonymous) has an \'extends\' array that contains a string ("some-string") at index 0. ' +
"This is a feature of eslint's `defineConfig()` helper and is not supported by typescript-eslint. " +
'Please provide a config object instead.',
);
});

it('strips nullish extends arrays from the config object', () => {
expect(
tseslint.config({
// @ts-expect-error purposely testing invalid values
extends: null,
files: ['files'],
}),
).toEqual([{ files: ['files'] }]);
});

it('complains when given an object with an invalid name', () => {
expect(() =>
tseslint.config({
extends: [],
// @ts-expect-error purposely testing invalid values
name: 42,
}),
).toThrow(
"tseslint.config(): Config at index 0 has a 'name' property that is not a string.",
);
});
});