Fix comments handling for for-statements that body is expression statements

[sosukesuzuki]

Description

Fixes #9812

Checklist

• I’ve added tests to confirm my change works.
• (If the change is user-facing) I’ve added my changes to changelog_unreleased/*/XXXX.md file following changelog_unreleased/TEMPLATE.md.
• I’ve read the contributing guidelines.

✨Try the playground for this PR✨

[fisker]

Excluding ExpressionStatement seems a good way, but should we do something about BlockStatement and EmptyStatement?

Prettier pr-9829
Playground link

--parser babel

Input:

for (const p of ['fullName', 'organ', 'position', 'rank'])
// @ts-expect-error
{form.setValue(`${prefix}.data.${p}`, response[p])}

for (const p of ['fullName', 'organ', 'position', 'rank'])
// @ts-expect-error
{}

for (const p of ['fullName', 'organ', 'position', 'rank'])
// @ts-expect-error
;

Output:

// @ts-expect-error
for (const p of ["fullName", "organ", "position", "rank"]) {
  form.setValue(`${prefix}.data.${p}`, response[p]);
}

// @ts-expect-error
for (const p of ["fullName", "organ", "position", "rank"]) {
}

for (const p of ["fullName", "organ", "position", "rank"]);
// @ts-expect-error

[sosukesuzuki]

@fisker Yes, but it's inconsistent with if, for and switch. I'll create another PR to make them consistent after this is merged.

Prettier 2.2.1
Playground link

--parser babel

Input:

if (foo) {
  // foo
}

// foo
for (;;) {}

switch (
  bar
  // foo
) {
}

Output:

if (foo) {
  // foo
}

// foo
for (;;) {}

switch (
  bar
  // foo
) {
}

[thorn0]

Did you try not to special-case ExpressionStatement and instead check that the following node isn't the body of the loop?

This handleForComments function was added in #901 to solve #886.

Extending its effect to ForStatement nodes doesn't seem to be a good idea:

Prettier pr-9829
Playground link

--parser babel

Input:

for (
  a = 1;
  // this condition is tricky:
  a === b || a === c;
  a++
) {
  console.log()
}

Output:

// this condition is tricky:
for (a = 1; a === b || a === c; a++) {
  console.log();
}

Would be good to find a way to remove this function and find a better solution for #886 as the current one can change the order of comments:

Prettier 2.2.1
Playground link

--parser babel

Input:

for (/*a*/a
/*b*/
of b) break

Output:

/*b*/
for (/*a*/ a of b) break;

[thorn0]

These issues related to comments are really hard. Fixing individual edge cases we seem to be never sure we don't break other edge cases at the same time.