🐛 Unable to migrate ESLint configuration that extends @antfu/eslint-config

[Kamillaova]

Environment information

CLI:
  Version:                      1.9.4
  Color support:                true

Platform:
  CPU Architecture:             aarch64
  OS:                           macos

Environment:
  BIOME_LOG_PATH:               unset
  BIOME_LOG_PREFIX_NAME:        unset
  BIOME_CONFIG_PATH:            unset
  NO_COLOR:                     unset
  TERM:                         "xterm-256color"
  JS_RUNTIME_VERSION:           "v22.8.0"
  JS_RUNTIME_NAME:              "node"
  NODE_PACKAGE_MANAGER:         unset

Biome Configuration:
  Status:                       Loaded successfully
  Formatter disabled:           false
  Linter disabled:              false
  Organize imports disabled:    false
  VCS disabled:                 false

Workspace:
  Open Documents:               0

What happened?

1. git clome https://github.com/Kamillaova/biome-eslint-migration-error-mre
2. direnv allow # or skip
3. pnpm i --frozen-lockfile
4. biome migrate eslint --write # or node_modules/.bin/biome without direnv

./eslint.config.js:1:1 deserialize ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Incorrect type, expected an array, but received an object.

  > 1 │ {"_operations":[null],"_operationsOverrides":[],"_operationsResolved":[],"_renames":{"@eslint-react":"react","@eslint-react/dom":"react-dom","@eslint-react/hooks-extra":"react-hooks-extra","@eslint-react/naming-convention":"react-naming-convention","@stylistic":"style","@typescript-eslint":"ts","import-x":"import","n":"node","vitest":"test","yml":"yaml"},"_pluginsConflictsError":{}}
      │ ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    2 │


migrate ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━

  ✖ Migration has encountered an error: Could not deserialize the Eslint configuration file

Expected result

Successful migration

Code of Conduct

• I agree to follow Biome's Code of Conduct

[pnodet]

From what I can see the issue might be caused by the config returning a promise instead of an array

[ematipico]

Are there really cases where a configuration might be a promise?

[Kamillaova]

Are there really cases where a configuration might be a promise?

Probably, literally @antfu/eslint-config. And eslint works fine with this configuration.

[siketyan]

it seems using top-level await for resolving the config antfu/eslint-config#323

[ematipico]

That's very unfortunate, I'm not sure we can support this configuration with the current infrastructure. We rely on node and the result given by the executed eslint configuration file.

To support it, it means we need to ship a shim just to resolve the promise, very inconvenient. cc @Conaclos who worked on the feature

[Kamillaova]

Can you provide the command with which biome tries to evaluate the config?

[siketyan]

The config is loaded in

biome/crates/biome_cli/src/execute/migrate/node.rs

Line 7 in 5fa96f0

pub(crate) fn load_config(specifier: &str) -> Result<Resolution, CliDiagnostic> {

.

I noticed it's not a top-level await, just the default export is a Promise. It seems Biome already supports TLA, so export default await antfu(...) can be a workaround?

[siketyan]

Maybe we can support such a config by flattening the Promise?
#5255

[Kamillaova]

  ✖ Migration has encountered an error: `node` was invoked to resolve './eslint.config.js'. This invocation failed with the following error:
    [eval]:15
    } import('./eslint.config.js').then((c) => c.default).then((c) => console.log(JSON.stringify(uncycle(c))))
                                                                                       ^

    TypeError: Converting circular structure to JSON
        --> starting at object with constructor 'Object'
        |     property 'configs' -> object with constructor 'Object'
        |     property 'flat/base' -> object with constructor 'Array'
        |     ...
        |     property 'plugins' -> object with constructor 'Object'
        --- property 'jsonc' closes the circle
        at JSON.stringify (<anonymous>)
        at [eval]:15:84

    Node.js v22.8.0

:(

[pnodet]

I think another part of the issue is that the antfu config doesn't return an array of eslint config objects in a typical way, it returns a Promise that resolves to a FlatConfigComposer

import { FlatConfigComposer } from 'eslint-flat-config-utils';

[Kamillaova]

Idk, but I think this project might be useful for exploring how to most correctly convert a flat configuration into an object with settings of eslint, etc.

https://github.com/eslint/config-inspector

[pnodet]

for people running into this issue, I used eslint print-config to extract the resulting configs and passed it to biome migrate.

[Kamillaova]

@pnodet

Oops! Something went wrong! :(

ESLint: 9.17.0

No files matching the pattern "print-config" were found.
Please check for typing mistakes in the pattern.

[Conaclos]

for people running into this issue, I used eslint print-config to extract the resulting configs and passed it to biome migrate.

Note that eslint --print-config prints the resolved configuration for a given path. This can be ok if you apply the same config on all files. Usually this truncates the config. This is why we don't use it internally and invoke node ourselves.

Regarding the current issue, we could perhaps use await for awaiting any Promise or plain value.

[Kamillaova]

eslint --print-config

Value for 'print-config' of type 'path::String' required.
You're using eslint.config.js, some command line flags are no longer available. Please see https://eslint.org/docs/latest/use/command-line-interface for details.

[siketyan]

@Kamillaova Could you try eslint --print-config eslint.config.js?

[Kamillaova]

@siketyan https://gist.github.com/Kamillaova/ec468052555b88cf0f63850633888f26

[pnodet]

@Conaclos yes, this is a dirty workaround. Regarding the current issue there are two underlying problems: the fact that it can return a promise and the fact that the promise here is not an array but instead a FlatConfigComposer