import/no-cycle crashing with external ESM modules (TypeError: Cannot read properties of null)

[ernestostifano]

Minimum reproduction here (see README).

The Issue

(Please note that eslint-import-resolver-exports has been patched in this project to provide some logs)

1. Run yarn lint:ok
2. Linting is completed successfully
3. Run yarn lint:not-ok
4. Linting fails with the following error:

Oops! Something went wrong! :(

ESLint: 8.57.1

TypeError: Cannot read properties of null (reading '/Users/username/repositories/eslint-plugin-import-issue-1/src/not-ok.js')
Occurred while linting /Users/username/repositories/eslint-plugin-import-issue-1/src/not-ok.js:1
Rule: "import/no-cycle"
    at checkSourceValue (/Users/username/repositories/eslint-plugin-import-issue-1/node_modules/eslint-plugin-import/lib/rules/no-cycle.js:116:59)
    at checkSourceValue (/Users/username/repositories/eslint-plugin-import-issue-1/node_modules/eslint-module-utils/moduleVisitor.js:32:5)
    at checkSource (/Users/username/repositories/eslint-plugin-import-issue-1/node_modules/eslint-module-utils/moduleVisitor.js:38:5)
    at ruleErrorHandler (/Users/username/repositories/eslint-plugin-import-issue-1/node_modules/eslint/lib/linter/linter.js:1076:28)
    at /Users/username/repositories/eslint-plugin-import-issue-1/node_modules/eslint/lib/linter/safe-emitter.js:45:58
    at Array.forEach (<anonymous>)
    at Object.emit (/Users/username/repositories/eslint-plugin-import-issue-1/node_modules/eslint/lib/linter/safe-emitter.js:45:38)
    at NodeEventGenerator.applySelector (/Users/username/repositories/eslint-plugin-import-issue-1/node_modules/eslint/lib/linter/node-event-generator.js:297:26)
    at NodeEventGenerator.applySelectors (/Users/username/repositories/eslint-plugin-import-issue-1/node_modules/eslint/lib/linter/node-event-generator.js:326:22)
    at NodeEventGenerator.enterNode (/Users/username/repositories/eslint-plugin-import-issue-1/node_modules/eslint/lib/linter/node-event-generator.js:340:14)

The Details

• yarn lint:ok lints ./src/ok.js file with the following content:

import {default as inquirer} from 'inquirer';

• yarn lint:not-ok lints ./src/not-ok.js file with the following content:

import {default as figures} from 'figures';

• inquirer has the following relevant package.json fields:

{
    "type": "module",
    "exports": {
        "./package.json": "./package.json",
        ".": {
            "import": {
                "types": "./dist/esm/index.d.ts",
                "default": "./dist/esm/index.js"
            },
            "require": {
                "types": "./dist/commonjs/index.d.ts",
                "default": "./dist/commonjs/index.js"
            }
        }
    },
    "main": "./dist/commonjs/index.js",
    "module": "./dist/esm/index.js",
    "types": "./dist/commonjs/index.d.ts"
}

• figures has the following relevant package.json fields:

{
    "type": "module",
    "exports": {
        "types": "./index.d.ts",
        "default": "./index.js"
    }
}

• The important main difference is that inquirer is a hybrid package with both ESM and CJS entry points, whether figures is ESM only.
• Using the following settings, we make so that require condition is preferred over import condition:

{
    "import/resolver": {
        "exports": {
            "require": true
        }
    }
}

• So, inquirer is loaded in CJS format, while figures is loaded in ESM, which is what is making ESLint crash. In fact, if we go into the index.js of figures and remove all ESM import/export statements, the issue goes away.

• So, it would seem that ESM is supported in project files, but not inside node_modules files, but the strange things are:

  • If we remove eslint-import-resolver-exports from the settings, the issue goes away, even if the resolver is doing its job flawlessly (see logs). But we loose support for exports.
  • The issue seems to not be present when using eslint-import-resolver-typescript.
  • It is like if eslint-import-resolver-exports was missing something in the returned data or something.

Finally, the most strange thing to me is that if we tweak eslint-import-resolver-exports to skip external modules, or just figures in this case, the issue also goes away.

Also, the following makes the issue go away:

{
    "import/no-cycle": [
        "error",
        {
            "ignoreExternal": true
        }
    ]
}

(even if, as a side effect, ignoreExternal seems to increase linting time instead of reducing it as I would have expected)

So, is import/no-cycle really checking external modules? Or it is just working because the external files are not being resolved in most cases?

Is it an issue with eslint-import-resolver-exports?

I am available to work on this (I already adopted eslint-import-resolver-exports and will publish an updated version of it in the future).

[ljharb]

If the issue only occurs when eslint-import-resolver-exports is used, then yes, it's a bug on that resolver.