Automatically add crate to workspace with cargo new

[czipperz]

I think it would make sense if there was a flag to cargo new such as --workspace that would add the new crate to the workspace. There is already workspace detection:

~/rust-comp master $ cargo new --lib abc
warning: compiling this new crate may not work due to invalid workspace configuration

current package believes it's in a workspace when it's not:
current:   /home/czipperz/rust-comp/abc/Cargo.toml
workspace: /home/czipperz/rust-comp/Cargo.toml

this may be fixable by adding `abc` to the `workspace.members` array of the manifest located at: /home/czipperz/rust-comp/Cargo.toml
Alternatively, to keep it out of the workspace, add the package to the `workspace.exclude` array, or add an empty `[workspace]` table to the package's manifest.
Created library `abc` package

So it probably wouldn't be too hard to have a way to automate the step of

adding abc to the workspace.members array

[Centril]

This should be filed over at https://github.com/rust-lang/cargo/issues/.

[czipperz]

Brilliant it's already in motion over there rust-lang/cargo#6378