"rustup add target ..." could warn user that they meant "rustup target add ..."

[gmatht]

Problem you are trying to solve

The following error message isn't as helpful as it could be:

$ rustup add target x86_64-unknown-linux-gnux32
error: unrecognized subcommand 'x86_64-unknown-linux-gnux32'

Usage: rustup target <COMMAND>

For more information, try '--help'.

Solution you'd like

I think it would be more useful if we added: Did you mean "rustup target add x86_64-unknown-linux-gnux32"?.

Notes

"add target" is the more natural language way of writing the command, so I feel we should help users who make this mistake.

[djc]

It is a bit of a strange error. Experimenting:

djc-2021 ~ $ rustup add -h
error: invalid value 'add' for '[+toolchain]': error: "add" is not a valid subcommand, so it was interpreted as a toolchain name, but it is also invalid. To override the toolchain using the 'rustup +toolchain' syntax, make sure to prefix the toolchain override with a '+'

For more information, try '--help'.
djc-2021 ~ $ rustup add target x86_64-unknown-linux-gnux32
error: unrecognized subcommand 'x86_64-unknown-linux-gnux32'

Usage: rustup target <COMMAND>

For more information, try '--help'.
djc-2021 ~ $ rustup add target
Modify a toolchain's supported targets

Usage: rustup target <COMMAND>

Commands:
  list    List installed and available targets
  add     Add a target to a Rust toolchain
  remove  Remove a target from a Rust toolchain
  help    Print this message or the help of the given subcommand(s)

Options:
  -h, --help  Print help

Maybe our attempts to extract a toolchain throw it off? Or maybe clap could/should be improved here?

[rami3l]

It is a bit of a strange error. Experimenting:

djc-2021 ~ $ rustup add -h
error: invalid value 'add' for '[+toolchain]': error: "add" is not a valid subcommand, so it was interpreted as a toolchain name, but it is also invalid. To override the toolchain using the 'rustup +toolchain' syntax, make sure to prefix the toolchain override with a '+'

For more information, try '--help'.
djc-2021 ~ $ rustup add target x86_64-unknown-linux-gnux32
error: unrecognized subcommand 'x86_64-unknown-linux-gnux32'

Usage: rustup target <COMMAND>

For more information, try '--help'.
djc-2021 ~ $ rustup add target
Modify a toolchain's supported targets

Usage: rustup target <COMMAND>

Commands:
  list    List installed and available targets
  add     Add a target to a Rust toolchain
  remove  Remove a target from a Rust toolchain
  help    Print this message or the help of the given subcommand(s)

Options:
  -h, --help  Print help

Maybe our attempts to extract a toolchain throw it off? Or maybe clap could/should be improved here?

@djc This is the +toolchain shorthand breaking clap, as usual. Similar to #3156.