🐛 Buggy side-effect caused by previous fix that made biome.json(c) un-ignore-able

[KemingHe]

Environment information

Platform:
  CPU Architecture:             x86_64
  OS:                           linux

Environment:
  BIOME_LOG_DIR:                unset
  NO_COLOR:                     unset
  TERM:                         "xterm-256color"
  JS_RUNTIME_VERSION:           "v22.2.0"
  JS_RUNTIME_NAME:              "node"
  NODE_PACKAGE_MANAGER:         "pnpm/9.1.2"

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

Workspace:
  Open Documents:               0

What happened?

To replicate the issue (after setting up the same env as mine):

1. In your biome.json, specify:

{
  "$schema": "https://biomejs.dev/schemas/1.7.3/schema.json",
  ...
  "json": {
      "formatter": {
        "trailingCommas": "all"
      }
    },
  ...
}

2. Run npx biome check --apply . (or yarn, or npmp, or predefined script in package.json);

3. biome.json will be formatted with trailing commas, which breaks the json standard for a root level config data file. To demonstrate, run npx biome check --apply . again and receive this error:

✖ Expected a property but instead found '}'.
  
    51 │     },
    52 │   },
  > 53 │ }
       │ ^
    54 │ 

4. Furthermore, merge fix: the file biome.json can't be ignored #1531 specified biome.json to be un-ignore-able, meaning that while the rest of the **/*.json files can be ignored or fine-grained controlled to add/not add commas (i.e. package.json), biome.json will always be incorrectly formatted.

Expected result

biome.json should be (by design, not by user choice) untouched by the trailing comma formatting option.

I would further suggest that user would not be able to specify to apply formatting to the file to avoid confusion.

In short:
Given the trailingCommas formatter for json is set to all
When running npx biome check --apply .
Then biome.json should not be affected

Code of Conduct

• I agree to follow Biome's Code of Conduct

[KemingHe]

For those come across here looking for a workaround, here's what you need to do:

"json": {
    "formatter": {
      "trailingCommas": "none"
    }
  },

And keep the discussion going so our wonderful maintainers can see this issue. ❤️

[dyc3]

I'd like to give this a shot.

[nhedger]

I'd like to give this a shot.

Thanks, assigned!