Allow overriding the toolchain file

README.md

@@ -42,7 +42,9 @@ jobs:
 ## Inputs
 
 All inputs are optional.
-If a [toolchain file](https://rust-lang.github.io/rustup/overrides.html#the-toolchain-file) (i.e., `rust-toolchain` or `rust-toolchain.toml`) is found in the root of the repository, its `toolchain` value takes precedence.
+If a [toolchain file](https://rust-lang.github.io/rustup/overrides.html#the-toolchain-file) (i.e., `rust-toolchain` or `rust-toolchain.toml`) is found in the root of the repository and no `toolchain` value is provided, all items specified in the toolchain file will be installed.
+If a `toolchain` value is provided, the toolchain file will be ignored.
+If no `toolchain` value or toolchain file is present, it will default to `stable`.
 First, all items specified in the toolchain file are installed.
 Afterward, the `components` and `target` specified via inputs are installed in addition to the items from the toolchain file.
 

action.yml

@@ -15,7 +15,6 @@ inputs:
   toolchain:
     description: "Rust toolchain specification -- see https://rust-lang.github.io/rustup/concepts/toolchains.html#toolchain-specification"
     required: false
-    default: "stable"
   target:
     description: "Target triple to install for this toolchain"
     required: false
@@ -107,9 +106,9 @@ runs:
         fi
       if: runner.os != 'Windows'
       shell: bash
-    - name: rustup toolchain install ${{inputs.toolchain}}
+    - name: rustup toolchain install ${{inputs.toolchain || 'stable'}}
       run: |
-        if [[ -f "rust-toolchain" || -f "rust-toolchain.toml" ]]
+        if [[ -z "$toolchain" && ( -f "rust-toolchain" || -f "rust-toolchain.toml" ) ]]
         then
           # Install the toolchain as specified in the file
           # Might break at some point: https://github.com/rust-lang/rustup/issues/1397
@@ -121,10 +120,15 @@ runs:
             rustup target add ${targets//,/ }
           fi
         else
-          rustup toolchain install ${{inputs.toolchain}}${{steps.flags.outputs.targets}}${{steps.flags.outputs.components}} --profile minimal${{steps.flags.outputs.downgrade}} --no-self-update
-          rustup default ${{inputs.toolchain}}
+          if [[ -z "$toolchain" ]]
+          then
+            toolchain=stable
+          fi
+          rustup toolchain install $toolchain${{steps.flags.outputs.targets}}${{steps.flags.outputs.components}} --profile minimal${{steps.flags.outputs.downgrade}} --no-self-update
+          rustup default $toolchain
         fi
       env:
+        toolchain: ${{inputs.toolchain}}
         targets: ${{inputs.target}}
         components: ${{inputs.components}}
       shell: bash