std::process::Command should probably implement Display

[matklad]

At the moment, Command does not implement Display. However, it's often useful to display Command for the end user, the most common case being that the command failed, and you want to display an error message. If cmd.to_string() returned something like cargo --metadata --manifest-path ./foo/Cargo.toml, that would be sweet.

It's also instructive to compare it with Paths. Path deliberately doesn't implement display directly, and the reason for that (I think) is not to make people thing about non-text path when displaing paths, but to make it harder to miss-use string formatting for path operations. IE, we don't want to people doing

let path = PathBuf::from(format!("{}/{}", base, name))

, as that doesn't handle bag-of-bytes paths.

For Command, I don't think to_string() can be missused in a similar manner, so adding Display seems like a clear win to me.

[the8472]

There's some misuse potential if someone tries to copy-paste and manually reexecute the output, which may not work if arguments contain whitespaces or are (similar to paths) bags of bytes.

[RalfJung]

If cmd.to_string() returned something like cargo --metadata --manifest-path ./foo/Cargo.toml, that would be sweet.

As @the8472 indicated, arguments should be properly escaped when needed to make this unambiguous.