Tolerate trailing commas in jsonc format

[alexreg]

Would it be possible to add tolerance for trailing commas to the jsonc (JSON With Comments) format? Even as an optional setting that is off by default. While I can understand not adding support to the json (spec-compliant) format, there doesn't seem to be a good reason not to add it (either on automatically or configurable) to jsonc.

In case there's any doubt over what I mean, here's an example.

{
    "foo": 123,
    "bar": [
        "abc",
        "def",
        "ghi", // trailing comma: okay!
    ], // trailing comma: okay!
}

[aeschli]

We had that, but changed it back to warn about commas. See #43825

JSONC is not a standard, but there are several tools that use JSON with comment such as eslint and tsconfig.
However, some of fhem don't accept the trailing commas. The editor would not complain and users would only find out at runtime that there's a trailing comma.
After multiple complaints we changed the default to warn.

However, in our VSCode settings files, trailing commas are accepted. This knowledge comes in through the JSON schema of the settings files. If the schema says "allowTrailingCommas": true, then it's not warned.

I want to leave this as is is now. Do you have a schema for your file?

[alexreg]

Ah, I see, thanks for explaining. I think you're right... many "jsonc" parsers accept trailing commas, while many don't. The Python one that I'm using happily does (and indeed I chose it partly for that reason).

Indeed, I was the one (as far as I'm aware) who requested the allowTrailingCommas feature for settings files, and that's great. :-)

No, I don't have a JSON schema. Maybe a setting like allowTrailingCommas could be added to the [json] language section in VS Code settings? Ideally this would be configurable on a per-directory or even per-file basis, but I suppose that comes down to how VS Code workspace settings work in general. Perhaps support for that has recently been added?

[aeschli]

We don't have folder/file based settings. I think there's a feature request.
But adding a schema is easy. It can also be done in the user settings:

	"json.schemas": [{
		"fileMatch": ["foo.jsonc"],
		"schema": {
			"allowTrailingCommas": true
		}
	}]

[alexreg]

Oh, I thought you meant JSON Schema. That's great, thank you.

[aeschli]

"schema" is for user defined JSON schemas. allowTrailingCommas is just a (internal) VSCode extension of JSON schema.