add rustfmt.toml

[pgherveou]

Copying the fmt from polkadot-sdk, without a sane configuration, rustfmt preserve local style which can produce a lot of unnecessary formatting diff

[xermicus]

without a sane configuration it's hard to not produce a lot of diff when running cargo fmt locally

But this means you configured your system away from the standard configuration? FWIW I never had any issues with formatting in any Rust codebase except when working with the polkadot-sdk. Can you elaborate a bit more why this is required?

[pgherveou]

take this PR #179 that I rebased on top of this one
without the .rustmft.toml, run cargo fmt does not fix all the formatting diff.

see this PR #181 where I removed the .rustfmt.toml, it creates a lot of formatting diff that should not be in the PR even though I ran cargo fmt and CI is passing

[xermicus]

I see, very unexpected to me that cargo fmt --all does, well, not format all.

Really don't get it. Running the formatter on main creates no changes. In your PR branch it re-formats (otherwise untouched) files. Not sure what's going on and why. Just ape it in.

[pgherveou]

yeah by default rustfmt preserve local style which is not great when multiple people work on a project with different version config of rustfmt