DICTIONARIES.md

Dictionaries

Polyjuice uses JavaScript objects to find a proper translation for a given rule. The object has the rule name to be translated as key and variable options as its value.

Basically, there is a truth function that will be used to test the value of the rule to be translated, and then its output is going to be matched against a truth table of default values of the destination tool.

The truth function is currently default for all languages, and its implementation is as follows.

var fn = function(input) {
  if (typeof input === 'number') {
    return true
  }

  return input ? true : false
}

It tells that if the value of the rule is a number, then it is considered true otherwise it is true based on JavaScript existence test. An example of a truth table is shown below.

{
  "true": 2,
  "false": 0
}

Possible rule values

Function

module.exports = function(__current__, value) {
  return {
    'rule-in-eslint': [2, value]
  }
}

This format tells the interpreter that you will return an object containing all the key/value that should be used. It is useful when you either want to omit a rule or when you want to consider several rules. You must return an object, even if empty.

String

module.exports = 'rule-in-eslint'

This format tells the interpreter that those rules are equivalent. Therefore, using the truth function on the value it gets the corresponding default true/false value from the truth table (or copy it if a number). I.e. if rule-in-jshint': true is in the source file, 'rule-in-eslint': 2 will be generated.

Array

module.exports = ['rule-in-eslint-1', 'rule-in-eslint-2']

This will work just as above, applying it to every string in the array.

Object

module.exports = {
  name: 'rule-in-eslint',
  truthy: function(__current__, value) {
    if (__current__) {
      return [2, __current__, value]
    }

    return [2, value]
  },
  falsy: [2, 'never']
}

Attributes

name

The attribute name is mandatory. It is the name in the target language.

eval

The attribute eval, if given, should be always a function and works much like using a function directly; However you do not need to provide the target as an object.

truthy

The attribute truthy, if function, is a shorthand for eval. It is called after the truth function decides the value is considered true. It can also be a string, an array, or any other value that can be directly applied.

falsy

The attribute falsy, if function, is a shorthand for eval. It is called after the truth function decides the value is considered false. It can also be a string, an array, or any other value that can be directly applied.

target

When converting from ESLint, the object must contain the target library it is converting to. ESLint conversions return an object whose keys are the targets read when transpiling a file. For instance:

'rule-in-eslint': {
  target: 'jshint',
  name: 'rule-in-jshint',
  truthy: true
}

FCFS Policy

Polyjuice has a FCFS policy for transpiling. Therefore, all transpiling functions have two arguments: __current__ and value. The first is the current value for the rule being assessed; It is useful when there is overlapping rules. The latter is the actual value of the rule being assessed in the moment. Bear in mind that the function priority is eval > test > truthy/falsy.