[TypeScript]: Comment is not printed ("Please report this error!")

Prettier 1.19.1 Playground link

--parser babel

Input:

const a: T</* comment*/> = 1;

Output:

Error: Comment "comment" was not printed. Please report this error!
    at https://prettier.io/lib/standalone.js:15543:15
    at Array.forEach (<anonymous>)
    at ensureAllCommentsPrinted (https://prettier.io/lib/standalone.js:15541:17)
    at coreFormat (https://prettier.io/lib/standalone.js:15592:5)
    at format (https://prettier.io/lib/standalone.js:15832:75)
    at formatWithCursor (https://prettier.io/lib/standalone.js:15848:14)
    at https://prettier.io/lib/standalone.js:31794:17
    at Object.format (https://prettier.io/lib/standalone.js:31802:14)
    at formatCode (https://prettier.io/worker.js:234:21)
    at handleMessage (https://prettier.io/worker.js:185:18)

Expected behavior:

It to not error, and to print the comment.

[Skalman]

@thorn0, I had assumed that this was the policy of Prettier, since Prettier does not format code with syntax errors.

Sorry for derailing the discussion. 😄

[G-Rath]

@Skalman I would say so - typically two bugs are less likely than one 😉

TS will parse and deal with anything,

True, which is because its robust and why prettier hasn’t dropped it in favor of babel 🙂

Generally, it’s better for user experience to be as robust and supporting as possible; while it wouldn’t be “wrong” to have prettier error, in doing so it means that a file with this code can never be formatted by prettier.

That’s actually one of the differences between eslint & typescript: eslint takes the erroring route bailing out at the first non-spec compliant or syntactically invalid character it runs into - the result is that ESLint just won’t lint your files if they have such code in them.

Meanwhile TypeScript strives to try and tell you as much about your code as possible, and so presses on when it encouters code that would make eslint error.

Neither is right or wrong - they’re serving different purposes, but I think for prettier in cases like these where the price of adding support is relatively cheap, it’s worth accepting them as a bug in prettier rather than hard failing 🙂

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The above is mostly IMO - I don’t speak for the prettier team, nor the eslint or typescript teams, but thats what I feel gives the best UX 🤷‍♂