[anodized-fmt] bug: should preserve comments

[mkovaxx]

At the moment, anodized-fmt relies on syn to parse and manipulate the spec attributes. The problem is that syn's parser treats comments as whitespace, so they're not represented in the input that the spec parser works with.

[mkovaxx]

Here's a potential approach: leptosfmt seems to implement a way to preserve comments:
leptosfmt/formatter/src/collect_comments.rs

[mkovaxx]

On a second look, the leptosfmt approach seems less applicable to anodized-fmt than I thought.

The core issue is that comment preservation needs a CST (concrete syntax tree) as opposed to an AST (abstract syntax tree). A CST preserves all information originally present in the source text, even if that information is ignored by transformation passes. Rust tokenization treats comments as whitespace, so they're missing from an AST. Building anodized-fmt on top of a CST-based structure seems like a better approach. The ra_ap_syntax and ra_ap_parser crates (on which rust-analyzer is based) seem like good shoulders for anodized-fmt to stand on.

Let's get there by taking small incremental steps. :)

[mkovaxx]

Another potential source of inspiration might be rust-reorder by @linustan. It uses syn paired with a way of tracking comments.