Previous node ignored if prettier-ignore is the last line

[imranolas]

Prettier 1.7.4
Playground link

Input:

Promise.resolve().then().then();

// prettier-ignore

Output:

Promise.resolve().then().then();

// prettier-ignore

Prettier 1.7.4
Playground link

Input:

Promise.resolve().then().then();

// prettier-ignore

Promise.resolve().then().then();

Output:

Promise.resolve()
  .then()
  .then();

// prettier-ignore

Promise.resolve().then().then();

When the // prettier-ignore comment is the last line, it ignores the previous node.

Expected behavior:

The first line should be formatted in both examples.

[azz]

This is likely due to the way comments with in prettier. They are attached to AST nodes, and in this case there's nothing after the comment so it is added as a dangling comment of the previous statement.

We could probably fix it by checking that the start index of the comment is less than the start index of the AST node.

I'm curious what caused you to find this issue? Was it just by observation, or is it causing a real issue?

[imranolas]

Granted it's very much an edge case. I actually found it whilst attempting to recreate another issue with prettier-ignore.

[duailibe]

@azz There's a case where we expect a prettier-ignore in a line after the node:

prettier/tests/ignore/ignore.js

Lines 59 to 60 in b53a426

	f( 1 )
	// prettier-ignore

So I guess that's intentional?

[azz]

Found it - looks like it is:

#671 (comment)

[azz]

Going to close this as there could be cases where people are relying on the lack of a leading check, and fixing this would break them for no good reason.