RUST-2019 Formatter for `Bson` ignores pretty printing `{:#}`

[mahmoud-moursy]

Versions/Environment

1. What version of Rust are you using?

rustc 1.82.0-nightly (506052d49 2024-08-16)

2. What operating system are you using?

Linux

3. What versions of the driver and its dependencies are you using? (Run
   cargo pkgid mongodb & cargo pkgid bson)

• bson: registry+https://github.com/rust-lang/crates.io-index#bson@2.11.0
• mongodb: N/A

4. What version of MongoDB are you using? (Check with the MongoDB shell using db.version())
   N/A
5. What is your MongoDB topology (standalone, replica set, sharded cluster, serverless)?
   N/A

Describe the bug

A clear and concise description of what the bug is.

BE SPECIFIC:

• What is the expected behavior and what is actually happening?
  Expected behaviour:

Bson formatting outputs the following:

{
  "key": "Hello world!"
}

What actually happens:

Bson formatting outputs the following:

{ "key": "Hello world!" }

• Do you have any ideas on why this may be happening that could give us a
  clue in the right direction?

If you implemented Display manually, then you need to manually check if the user passed in pretty-printing
as a parameter and then change your formatting based on that.

You can check it using formatter.alternate() in your Display implementation.

• Did this issue arise out of nowhere, or after an update (of the driver,
  server, and/or Rust)?
  The issue has likely existed for as long as the crate has.
• Are there multiple ways of triggering this bug (perhaps more than one
  function produce a crash)?
  Nope. Only one, specifically. Formatting with {:#?} produces correctly-formatted output.
• If you know how to reproduce this bug, please include a code snippet here:

let my_hashmap = HashMap::from([
  ("hello", "world!")
]);

let bson_document = bson::to_document(&my_hashmap);

// Incorrect formatting:
println!("{bson_document:#}");

// This, however, is correctly formatted:
println!("{bson_document:#?}");
// It is probably correctly formatted because the derive(Debug) implementation was used.

Thank you.

[abr-egn]

Thank you for the well-written ticket!

You're quite right that we're not respecting that flag currently; I've filed RUST-2019 to track that. This won't be high priority in our plan for this quarter but we'd certainly welcome a contribution to add it 🙂