Add option to ignore trailing commas

[aurelleb]

One of my use case for glaze is to load configuration files that can sometimes be hand edited, and a very common mistake when hand editing is to forget a trailing comma after rearranging an object.

It would be great if glz::opts could add an option to ignore such trailing commas

[stephenberry]

I understand the desire for this feature, but I'm wary of it, because it breaks the JSON specification. So, suddenly all your configuration files won't be able to load in tons of JSON libraries and won't pass JSON validators. I don't think breaking the specification is worth the slight benefit. Instead, I would recommend using a tool like VSCode to edit JSON files, so that it will syntax highlight your errors. Other editors will provide this feedback as well.

Also, trailing comma support would actually make parsing a little slower, because it adds another branch in parsing arrays.

If you want a more human friendly configuration format then I would recommend TOML, which Glaze also supports.

I'm open to hear your thoughts, feel free to comment below, but I'm going to close this issue for the reasons stated above.

[aurelleb]

Yeah, I understand the reasons behind the fact it's not a default, but like comments, I think it is something that you may still want under some circumstances.

As far as I know JSONC has the same shortcomings as this does, you can't parse it using non JSONC compliant parsers, and most parsers will reject it by default

That is why I think it could be an option that has to be explicitly specified.

I know about TOML, but it falls short when dealing with configuration files that have a lot of nesting, even with toml 1.1 multiline inline tables.

[stephenberry]

@aurelleb, I've moved this to discussions so more developers can find this and provide feedback.

Your argument about JSONC is good, but I feel it adds much more benefit than trailing commas, and it is supported as a standard by a number of tools.

You're correct about TOML and complex/nested structures. I do prefer JSON for configuration.

[aurelleb]

The JSONC spec has this really nice page about why it didn't add support for trailing commas: https://jsonc.org/trailingcommas

This page also indicates that trailing commas are supported by popular tools that are commonly configured with JSON, like vscode (although they discourage it). This is also supported by the Zed editor.

I think there is a huge intersection between using JSONC and also supporting trailing commas because both are designed to make JSON more suitable as an hand editable config language.

My use case is very similar to these two editors: my program is configured using a json file, which can be either hand edited or programatically modified through the GUI. If the file is hand edited and the user forgets a trailing comma, this error gets automatically fixed the next time it is reserialized (any config change).

That way, the impact on general compatibility with other parsers generally matter much less because the odds of the trailing commas being preserved are very low. Also, compatiblity with other parsers is generally less of a concern when it comes to config files that are tied to a specific applications, as they are very rarely used for other purposes than configuring said app.

This simply allow the user to quickly edit the config file without having to worry about this big annoyance that are trailing commas.

I honestly do think that this is a valid use case, but I can understand your focus on correctness. I simply think that providing a way to do it, when it is generally accepted for configuration, would be better than not having the option at all.

[stephenberry]

These are good points. I'll consider how much complexity this would add to the codebase, but I don't think it would be too much.