# Objective
When reviewing #18263, I noticed that `BevyManifest` internally stores a
`DocumentMut`, a mutable TOML document, instead of an `ImDocument`, an
immutable one. The process of creating a `DocumentMut` first involves
creating a `ImDocument` and then cloning all the referenced spans of
text into their own allocations (internally referred to as `despan` in
`toml_edit`). As such, using a `DocumentMut` without mutation is
strictly additional overhead.
In addition, I noticed that the filesystem operations associated with
reading a manifest and parsing it were written to be completed _while_ a
write-lock was held on `MANIFESTS`. This likely doesn't translate into a
performance or deadlock issue as the manifest files are generally small
and can be read quickly, but it is generally considered a bad practice.
## Solution
- Switched to `ImDocument<Box<str>>` instead of `DocumentMut`
- Re-ordered operations in `BevyManifest::shared` to minimise time spent
holding open the write-lock on `MANIFESTS`
## Testing
- CI
---
## Notes
I wasn't able to measure a meaningful performance difference with this
PR, so this is purely a code quality change and not one for performance.
---------
Co-authored-by: Carter Anderson <mcanders1@gmail.com>
dc7cb2a3e1