Support reading rust-toolchain file from another directory

[alsuren]

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• Is this related to the actions-rs Actions?
  If you think it's a problem related to Github Actions in general, use GitHub Community forum instead: https://github.community
• You've read the Contributing section about feature requests: https://github.com/actions-rs/.github/blob/master/CONTRIBUTING.md#feature-requests
• Is this something you can debug and fix? Send a pull request! Bug fixes and documentation fixes are welcome.
  • I think we found the bit of the code where you search for rust-toolchain file. Would like some input on naming/semantics of our with option though.

Motivation

Our github actions workflow requires us to have two repos checked out, so we use the checkout action like this:

        uses: actions/checkout@v2
        with:
          path: futurenhs-platform

so we have this work-around to make actions-rs/toolchain pick up our rust-toolchain file:

      - name: Make toolchain version available in current directory
        run: cp futurenhs-platform/rust-toolchain .

in https://github.com/FutureNHS/futurenhs-platform/pull/231/commits/8602258bb2ff07740ddc8522247d86d3fb50b7e4 I have a work-around to copy rust-toolchain from our repo checkout into the current working directory.

Workflow example

      - uses: actions/checkout@v2
        with:
          path: futurenhs-platform
      - name: Make toolchain version available in current directory
        run: cp futurenhs-platform/rust-toolchain .
      - uses: actions-rs/toolchain@v1
        with:
          toolchain-path: futurenhs-platform/rust-toolchain

(or possibly just path: futurenhs-platform?)

we thought about using working-directory: futurenhs-platform but this would have to be in a with block (it can only be top-level for run actions)

[lukepighetti]

I am also running into this issue. I have a monorepo and want to put rust-toolchain.toml in each projects folder, but actions-rs/toolchain@v1 doesn't recognize this as a valid location, even if the GitHub Actions working directory is set to the project folder