Option for (no) semi

[pre63]

I implemented a prototype for a option to remove the semi. It removes all the semi if semi=true. It's a brute force approach and does not account for the cases where not having a semi is a breaking change.

I'd be ready to add documentation and test if you are interested in merging this pr.

Then the next step would be adding specific logic for the cases where an absent semi is breaking. But it's more a v2 thing.

[vjeux]

Thank you for this! We do want to allow an option to print code without a semi-colon. However, we cannot ship this one as is as it would output code that doesn't have the same semantic.

For example

console.log();
[1, 2, 3].forEach(a => a);

would be transformed into

console.log()
[1, 2, 3].forEach(a => a)

which throws

Uncaught TypeError: Cannot read property '3' of undefined

as it is evaluated as

console.log()[1, 2, 3].forEach(a => a)

If you are willing to make an implementation that produces correct code, I'd love to merge it (but beware, it's not easy!)

[pre63]

@vjeux I agree it's a problem. In your opinion what would be the best outcome for this code?

console.log();
[1, 2, 3].forEach(a => a)

or

console.log()
;[1, 2, 3].forEach(a => a)

[vjeux]

I've never written code without semi-colons so I'm not sure. Do you know if there's a conventional way? Good places to look would be the standard project and what the autofix rule of eslint does.

[pre63]

There are 3 main problems that I know of.

1. The one you described

console.log()
[1, 2, 3].forEach(a => a)

evaluated to

console.log()[1, 2, 3].forEach(a => a)

2. the self calling function

console.log('hello')
(function(){
  console.log('world') // throws
}())

3. the return undefined statement

return
  { hello:world' }

becomes

return;
  { hello:world' };

I'll give it a try.

I'll add the semi at the beginning of the line because I think it's easier and because it's part of the standard. Eslint rule can always be adapted.

[vjeux]

There are many more, some examples:

for (;;);
console.log()

#634 (comment)

class A {
  a = 1;
  [b] = 2;
}

#12 (comment)

class B {
  set;
  foo(x){}
}

[lydell]

As far as I know, leading semi-colon is the convention.

console.log()
;[1, 2, 3].forEach(a => a)

The idea is to clearly show that a semi-colon is actually required there. If you put it after console.log() it might look like a mistake. Also, if the console.log() is moved, you'll have to remember to move the semi-colon appropriately.

[pre63]

@lydell I agree

[jlongster]

@pre63 Thank your for this PR. This is a feature that I was planning to work on and I would like to take it because it requires a lot of special work and also forces us to figure out how to run tests with it and without, and stuff like that. It's such a large feature that I think it's going to be easiest if I implement it. Is that OK? We're also not 100% committed to this feature yet; we want to explore the complexity of it and see if it's simple enough. If it's too buggy/complex we're not going to do it.

Sorry for the work you already put into it. Almost all other bugs/features are open for the taking but this one is different. Is it OK if we close this while I work on another PR?

[vjeux]

I'm going to close it in order to make the queue smaller as @jlongster mentioned.