Adding mapping between enum keys and values

[rickyp-uber]

Currently for enum generation keys and values are just unions and there is no way to put this data back together. This change will create a map object to allow referencing of one value to the other.

[CLAassistant]

All committers have signed the CLA.

[koulmomo]

You should add a test

[koulmomo]

don't bump package version, that will happen after the pull request is landed and a new version is released.

[rickyp-uber]

Unit test added

[rickyp-uber]

@keithkml mind taking a look?

[keithkml]

Hmmm, this kinda defeats the purpose of the type name suffix, which will lead to linting errors. Actually it looks like the previous change which added xxxKeys broke it too, but I didn't notice. Easy solution is to move the Map and Keys suffix into the call to transformName

[rickyp-uber]

Example Input:

typedef MyEnum EnumTypedef

enum MyEnum {
  OK = 1
  ERROR = 2
}

struct MyStruct {
  1: MyEnum f_MyEnum
  2: EnumTypedef f_EnumTypedef
}

Output

// @flow

// Generated by thrift2flow at Mon Jun 18 2018 15:14:45 GMT-0700 (PDT)

export type EnumTypedefType = $Keys<typeof MyEnumType>;

export const MyEnumType = {
  OK: 1,
  ERROR: 2
};

export type MyStructType = {|
  f_MyEnum: $Keys<typeof MyEnumType>,
  f_EnumTypedef: EnumTypedefType
|};

[rickyp-uber]

Note this also resolves the eslint error
https://github.com/gajus/eslint-plugin-flowtype#eslint-plugin-flowtype-rules-type-id-match

[keithkml]

I think this code would look a lot nicer (and this diff would be a lot smaller :) ) if you just stored this as a field, or even just declared a getter function for this value.