Formatter: Convert variable names to snake-case

[jfmengels]

Coming from other languages like Elm and JavaScript where the conventions are to have variables named in camel-case.

In Gleam, camel-case is forbidden and results in syntax errors, which I can very much understand as it should make for very consistent naming patterns.
My force of habit is strong, and I spend quite some time converting the camel-case names I write to snake-case, which is distracting from my goal at hand.

A suggestion I have that could make that easier, is have the formatter automatically convert names to snake-case.

For instance, the formatter could change the code like this

fn doSomething() { todo }
-->
fn do_something() { todo }

The compiler error already suggests this name change in the error message.

Same idea for references to consts/functions in expressions.

If this can be done reliably, then I can't think of many downsides (but I may not be familiar enough with the syntax).

One downside I can imagine is that if you've never written Gleam, and you don't ever see the error message that variables should be snake_case, then it will feel quite jarring to see a rename. Once you know it, I think it will be helpful though.

[jfmengels]

Alternatively, this could be an LSP code action. Requires more manual work from the user but it would be less surprising.

Some editors sometimes have a "Convert to snake_case" command which solves the problem, but it's not necessarily discoverable. Took me a few days to discover mine had that. An LSP code action would be a lot more discoverable.

[lpil]

Sounds good to me! I think we would only want to do this for definitions and not for referencing variables and functions. What do you think?

We'll need to make the parser permit uppercase names have the analyser emit an error if one is used in a definition.

[jfmengels]

I could see it used for both definitions and references, but I do imagine this being more surprising or annoying for references. I think it would be reasonable to start only with definitions, and at some point to have a branch where it also does it for references, and try to see how it feels.

Although it should probably be tried out by beginners, as seasoned Gleam developers will likely not write camelcase already (unless they also often work with camelcase languages).

[lpil]

For references it could "correct" to a value that type checks but isn't the value that the programmer intended to use. I'd like to not have anything that could make the programmer's code silently do the wrong thing.