Comments aren't preserved when modifying an existing stanrdard toml table with cargo add

[epage]

Problem

cargo add can modify existing entries, like adding more features. When using a standard table (as opposed to an inline table, see #10849), comments get deleted.

Steps

Note: steps are using this is a test case in cargo and these crates don't normally exist

With Cargo.toml:

[workspace]

[package]
name = "cargo-list-test-fixture"
version = "0.0.0"

[dependencies.your-face]
version="99999.0.0"  # Hello world
features=["eyes"]  # Goodbye moon

run

$ cargo add your-face -F features nose

and you'll get

[workspace]

[package]
name = "cargo-list-test-fixture"
version = "0.0.0"

[dependencies.your-face]
version = "99999.0.0"
features = ["eyes"]

Possible Solution(s)

There are two problems

• We drop the existing formatting
• We explicitly call table.fmt() which deletes all decor

The reason for the latter is so the trailing space in inline tables is removed when an item is no longer the last.

Notes

No response

Version

No response

[marcospb19]

@epage would the solution be to just remove the table.fmt() call and manually traverse toml_edit items to remove trailing spaces?

[weihanglo]

@marcospb19 I am not sure if this is that easy but definitely something people can experiment