Control of semicolon behaviour

Motivation

I’m using astring as part of an atom plugin to help with code generation. It would be great to be able to control whether semicolons are emitted, so that I can match the current style directives of the current project. Right now, semicolons are implemented as a whole bunch of state.write(';') instances.

It would be awesome to have a config option to control semicolon emission. I’m thinking that you could replace all those writes with a semantic state.terminate(), which can check if it should print a semicolon or not.

The only alternative to control this is to basically fork the entire baseGenerator, so you can remove all those writes.

[davidbonnet]

This could be handled through a custom output stream, that removes semicolons:

const output = {
  code: '',
  write(code) {
    switch (code) {
      case ';':
        break
      case ');':
        this.code += ')'
        break
      case 'debugger;':
        this.code += 'debugger'
        break
      default:
        this.code += code
        break
    }
  },
}

const { code } = astring.generate(ast, { output })

console.log('Code without semicolons:', code)

There are however two known issues to this:

1. Not all semicolons can be removed, in particular, when the next expression starts with a parenthesis.
2. Using a custom output stream has some performance hits.

Thus, a more precise handling is required. This could be a first step towards version 2. Pull requests are welcome.

[Mouradif]

@KFlash did you check my PR above ?