Multiline comment formatting not idempotent

[jhaber]

I'm seeing an issue with multiline comments getting extra indentation each time they get run through prettier-java

Input:

public class Example {
  
  public void method() {
    /*
      multiline comment
     */
  }
}

Output: (after running prettier ~5 times)

public class Example {

  public void method() {
    /*
                multiline comment
   */
  }
}

Each run of prettier seems to indent the comment a little more.

The issue doesn't manifest if each line of the comment is prefixed with an asterisk (although the formatting in this case still looks a little bit off), for example:

Input:

public class Example {

  public void method() {
    /*
     * multiline comment
     */
  }
}

Output:

public class Example {

  public void method() {
    /*
   * multiline comment
   */
  }
}

[jhaber]

I also tried running on #278 and got the same result

[clementdessoude]

Thank you for reporting this. It certainly comes from

prettier-java/packages/prettier-plugin-java/src/printers/prettier-builder.js

Lines 64 to 78 in 7a1873f

	function formatComment(comment) {
	const res = [];
	comment.image.split("\n").forEach(l => {
	if (l.match(/(\s+)(\*)(.*)/gm) && !l.match(/(\/)(\*)(.*)(\*)(\/)/gm)) {
	res.push(" " + l.trim());
	} else {
	res.push(l);
	}
	res.push(hardLineWithoutBreakParent);
	});
	if (res[res.length - 1] === hardLineWithoutBreakParent) {
	res.pop();
	}
	return res;
	}

which I didn't change in #278

[jhaber]

Thanks for investigating. I was curious how the javascript version handles comments and found this documentation:
https://prettier.io/docs/en/rationale.html#comments

When it comes to the contents of comments, Prettier can’t do much really. Comments can contain everything from prose to commented out code and ASCII diagrams. Since they can contain anything, Prettier can’t know how to format or wrap them. So they are left as-is. The only exception to this are JSDoc-style comments (block comments where every line starts with a *), which Prettier can fix the indentation of.

This matches some javascript testing I did. All of these:

/*
            * comment
      */

/*
* comment
*/

             /*
   * comment
      */

Were updated to:

/*
 * comment
 */

But if any line inside the comment didn't start with an asterisk, then the contents of the comment (and close comment tag) were left untouched. For example this was was not updated by prettier:

/*
      * line 1
              line 2
             */

However it does still seem to remove leading whitespace from the open comment tag, so this was updated to look like the previous example:

            /*
      * line 1
              line 2
             */

[jhaber]

To be clear I don't think it's imperative that the behavior is matched exactly, just thought this was an interesting datapoint

[clementdessoude]

Good insight ! That matches what I am thinking after taking a quick look at this issue