Trailing commas for type parameters in Flow with --trailing-comma=es5

[suchipi]

I'm not sure if this is the correct behavior or not, but I just moved from trailingComma: "all" to trailingComma: "es5" in our codebase at work, and was surprised to see these ones disappear.

Prettier 1.9.2
Playground link

--trailing-comma es5

Input:

type FooThisNameIsVeryLongSoThatItBreaksToTheNextLine = Something<FirstParam, SecondParam>;

Output:

type FooThisNameIsVeryLongSoThatItBreaksToTheNextLine = Something<
  FirstParam,
  SecondParam
>;

Prettier 1.9.2
Playground link

--trailing-comma all

Input:

type FooThisNameIsVeryLongSoThatItBreaksToTheNextLine = Something<FirstParam, SecondParam>;

Output:

type FooThisNameIsVeryLongSoThatItBreaksToTheNextLine = Something<
  FirstParam,
  SecondParam,
>;

This affects both flow and typescript.

Seeing as type parameters aren't valid ES5 anyway, should we maybe include trailing commas there even when using trailingComma: "es5"?

[suchipi]

Related: #3662 #3313

[duailibe]

Following that logic we could consider that "es5" == "all" since it's valid in TS anyway, not ES 😂

[suchipi]

Yeah I guess that's kinda weird... I'm looking at it from the flow perspective, though.

[vjeux]

@suchipi looks like an oversight to me. Feel free to fix it :)

[azz]

From memory, older versions of TS don't support trailing commas here, I think it was intentional. Might want to double check

[fisker]

Fixed by #14085