[Observation] #84145: comment after annotation causing invalid macro expansion

[ZevEisenberg]

Resolves #84145.

Before

This code would fail to compile:

@Observable
final class MyClass {
  @MainActor // some comment here
  var it = 0
}

This is because the comment after @MainActor was ending up as a prefix on the same line as the generated _it variable in the expanded code.

After

The code compiles because the _it variable is moved to a new line instead of at the end of the line with the comment.

[bnbarham]

Thanks for putting this up @ZevEisenberg!

[bnbarham]

IMO we'd actually want a newline on the modifiers if there are any, then a space on the var/let if there is, and a newline otherwise. Also need trivia on the added attribute, as otherwise it'll still be added after the comment.

[ZevEisenberg]

Is there a way you'd recommend making a test case to confirm what the output looks like? Right now I'm just relying on a test that confirms that the output compiles, but not what it actually looks like.

[bnbarham]

You can use -dump-macro-expansions. There should be a few tests that do that today

[jamieQ]

@bnbarham i discussed with Zev, and i'll try to push this forward here: #84833 – i took a stab at incorporating your feedback and adding some filecheck tests of (a portion of) the macro output. would appreciate any further input!

[ZevEisenberg]

Closed in favor of #84833, which has merged.