Default to ${{ runner.arch }} instead of to x64 (#114)

* If the user does not specify the `arch` input, default to `${{ runner.arch }}` (instead of defaulting to `x64`)

* Add a CI workflow that tests the default arch (i.e. tests what happens when the user does not specify the `arch` input)

.github/workflows/example-builds-defaultarch.yml

@@ -0,0 +1,33 @@
+name: Example builds (default arch)
+
+on:
+  push:
+    branches: ['main', 'master', 'releases/*']
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  test:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        julia-version: ['1']
+        os: [ubuntu-latest, macOS-latest, windows-latest]
+
+    steps:
+      - uses: actions/checkout@v1.0.0
+
+      - name: "Install dependencies"
+        run: |
+          npm install --legacy-peer-deps
+          npm run build
+          npm run pack
+
+      - name: "Set up Julia"
+        id: setup-julia
+        uses: ./
+        with:
+          version: ${{ matrix.julia-version }}
+      - run: julia --version
+      - run: julia --compile=min -O0 -e 'import InteractiveUtils; InteractiveUtils.versioninfo()'

README.md

@@ -46,7 +46,7 @@ This action sets up a Julia environment for use in actions by downloading a spec
     #
     # Note: you can use X64, X86, and ARM64 as synonyms for x64, x86, and aarch64, respectively.
     #
-    # Default: x64
+    # Defaults to the architecture of the runner executing the job.
     arch: ''
 
     # Set the display setting for printing InteractiveUtils.versioninfo() after installing.
@@ -129,7 +129,7 @@ jobs:
       matrix:
         julia-version: ['1.0', '1.2.0', '^1.3.0-rc1']
         os: [ubuntu-latest, windows-latest, macOS-latest]
-    
+
     steps:
       - uses: actions/checkout@v1.0.0
       - name: "Set up Julia"
@@ -155,7 +155,7 @@ jobs:
         exclude:
           - os: macOS-latest
             julia-arch: x86
-    
+
     steps:
       - uses: actions/checkout@v1.0.0
       - name: "Set up Julia"
@@ -182,7 +182,7 @@ jobs:
           - os: windows-latest
             julia-version: ['1.0.4']
             julia-arch: x86
-    
+
     steps:
       - uses: actions/checkout@v1.0.0
       - name: "Set up Julia"

action.yml

@@ -6,9 +6,9 @@ inputs:
     description: 'The Julia version to download (if necessary) and use. Example: 1.0.4'
     default: '1'
   arch:
-    description: 'Architecture of the Julia binaries. Defaults to x64.'
+    description: 'Architecture of the Julia binaries. Defaults to the architecture of the runner executing the job.'
     required: false
-    default: 'x64'
+    default: '${{ runner.arch }}'
   show-versioninfo:
     description: 'Display InteractiveUtils.versioninfo() after installing'
     required: false