How to install a Rust target for a specific rustup toolchain?

Question

I am using rustc and cargo on my 64-bit Windows machine to compile a 32-bit application. This work fine when using the stable toolchain, but when I try to use the beta toolchain it fails.

The beta toolchain was successfully installed with rustup install beta. In the project folder there is a .cargo/config file containing the following lines:

[build]
target = "i686-pc-windows-msvc"

[target.i686-pc-windows-msvc]
rustflags = ["-Ctarget-feature=+crt-static"]

When running cargo +beta build the following error occurs:

error[E0463]: can't find crate for `core`
  |
  = note: the `i686-pc-windows-msvc` target may not be installed

I have tried running rustup target add i686-pc-windows-msvc to fix the issue but it didn't help; rustup target list even displays it as "installed". Possibly this command only adds the target for stable, and I couldn't find out how to specify the beta toolchain.

How can I add another (non-default) target for the beta toolchain?

Answer 1

Read the help for rustup target add:

$ rustup target add --help
rustup-target-add
Add a target to a Rust toolchain

USAGE:
    rustup target add [OPTIONS] <target>...

FLAGS:
    -h, --help    Prints help information

OPTIONS:
        --toolchain <toolchain>    Toolchain name, such as 'stable', 'nightly', or '1.8.0'. For more information see
                                   `rustup help toolchain`

Thus you want:

rustup target add i686-pc-windows-msvc --toolchain beta

I believe it will add the target to the "current" toolchain by default, so you could also do:

rustup override set beta               # in your project directory
rustup target add i686-pc-windows-msvc #
cargo build                            # no more +beta

---

rustup target list even displays it as "installed"

Read the help for rustup target list:

$ rustup target list --help
rustup-target-list
List installed and available targets

USAGE:
    rustup target list [OPTIONS]

FLAGS:
    -h, --help    Prints help information

OPTIONS:
        --toolchain <toolchain>    Toolchain name, such as 'stable', 'nightly', or '1.8.0'. For more information see
                                   `rustup help toolchain`

Thus you want:

rustup target list --toolchain beta