deno-fmt-ignore behavior in JSONC is unintuitive

[kidonng]

deno fmt doesn't like trailing commas in JSONC, which is mostly fine since we can just let it ignore them, but the behavior is unintuitive.

This works:

{
  // deno-fmt-ignore
  "tasks": {
    "foo": "echo bar",
  }
}

$ deno fmt --check
Checked 240 files

But this doesn't work, which places the comment to the desired location:

{
  "tasks": {
    // deno-fmt-ignore
    "foo": "echo bar",
  }
}

$ deno fmt --check

from /workspaces/lume/tests/assets/deno.jsonc:
4 | -    "foo": "echo bar",
4 | +    "foo": "echo bar"

error: Found 1 not formatted file in 240 files

This doesn't work either, though I'm not sure if other formatters support this comment style:

{
  "tasks": {
    "foo": "echo bar", // deno-fmt-ignore
  }
}

[dsherret]

The reason why this occurs is because the comma is controlled by the parent object and in this case the // deno-fmt-ignore only applies to "foo": "echo bar" and not "foo": "echo bar",.

I could update the behaviour to keep the trailing comma into account, but adding ignore comments to keep trailing commas seems kind of extreme to me. I've opened dprint/dprint-plugin-json#9

[kidonng]

the comma is controlled by the parent object

Ah, that explains it. Not very obvious when most of the time the ignore comment is next to the thing being ignored though.

adding ignore comments to keep trailing commas seems kind of extreme to me

This is a test file for JSONC parsing. I do agree real use cases are rare.