notramo (Oct 09 2026 at 12:35): notramo (Oct 09 2026 at 12:35):What is the cause of the insane amount of comment deletion bugs? Is it caused by the lexer or parser architecture?
notramo (Oct 09 2026 at 12:36):Is it not fuzzed? Or is it impossible to track the amount of comments before and after formatting?
Anton (Oct 09 2026 at 12:46):We have fuzzing but it may not be set up to check deleted comments. Feel free to make an issue for that.
notramo (Oct 09 2026 at 12:49):Why does it happen often with comments but not with other lexemes?
notramo (Oct 09 2026 at 12:56):I opened these:
https://github.com/roc-lang/roc/issues/12145
https://github.com/roc-lang/roc/issues/12146
Anton (Oct 09 2026 at 13:51):Comments do not affect the execution of the program so that may be one of the reasons why they are handled differently.
Anton (Oct 09 2026 at 13:55):Comments can also be in between a ton of different elements which probably leaves a lot of edge cases.
Luke Boswell (Oct 09 2026 at 17:04):Aren't comments also special in that we dont tokenize them, we do something different and keep them out of the AST. I'd have to look at it again, but I thought we dont include them to keep compilation leaner.
notramo (Oct 09 2026 at 17:09):Does the Roc parser construct a CST? Formatters should work from CST, it's simpler and less error-prone.
Luke Boswell (Oct 09 2026 at 17:13):I'm not so familiar with a CST specifically or how Roc's AST would differ from that. The choice to do it this way was made for performance reasons, at the cost of a more complicated formatter If I remember correctly. I know we experimented with a lot of different ways of doing things over the years.
I would assume @Anthony Bullard or @Joshua Warner would have more background here for you.
notramo (Oct 09 2026 at 17:21):I'm not so familiar with a CST specifically or how Roc's AST would differ from that.
Some parsers construct a Concrete Syntax Tree after tokenization, which is then lowered to an AST. It's sometimes used by tools that provide autoformatting and LSP support. I'm not familiar with the Roc compiler at all, so that's why I asked whether it has CST, or directly parse to an AST.
Last updated: Oct 15 2026 at 17:56 UTC