Support installing just in mulitple operating systems.

This follows the official just instructions for [installing pre-built
binaries](https://github.com/casey/just#pre-built-binaries).

However, the current version of https://just.systems/install.sh doesn't
quite work in windows. I have fixed that and [proposed the changes
upstream](casey/just#1474), and include a copy
of the fixed script in this repo for now.

As part of this, have added tests for this action, which runs on
multiple OSs, in order to test the cross platfoem installation

Also, allow installing a specific version of just.

.github/workflows/test.yaml

@@ -0,0 +1,32 @@
+name: self test
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+
+jobs:
+  test:
+    strategy:
+      matrix:
+        os: 
+          - ubuntu-20.04
+          - ubuntu-22.04
+          - windows-2019
+          - windows-2022
+          - macOS-12
+          - macOS-11
+    runs-on: ${{ matrix.os }}
+
+    steps:
+    - uses: actions/checkout@v3
+      with:
+        fetch-depth: 0
+    - name: self test
+      uses: ./
+      with:
+        install-just: true
+    - name: test just works
+      shell: bash
+      run: just test

action.yml

@@ -8,6 +8,9 @@ inputs:
   install-just:
     description: 'If true, this installs Just'
     required: false
+  just-version:
+    description: 'Specific version of just to install'
+    default: 1.9.0
 
 runs:
   using: 'composite'
@@ -24,7 +27,8 @@ runs:
         cache-dependency-path: requirements.*.txt
     - name: Install just
       if: ${{ inputs.install-just }}
+      shell: bash
       run: |
-        curl -L https://github.com/casey/just/releases/download/1.9.0/just-1.9.0-x86_64-unknown-linux-musl.tar.gz \
-         | tar -xzf - --directory /usr/local/bin just
-      shell: bash
+        mkdir -p "$HOME/bin"
+        bash install-just.sh --to "$HOME/bin" --tag "${{ inputs.just-version }}"
+        echo "$HOME/bin" >> $GITHUB_PATH

install-just.sh

@@ -0,0 +1,167 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+if [ ! -z ${GITHUB_ACTIONS-} ]; then
+  set -x
+fi
+
+help() {
+  cat <<'EOF'
+Install a binary release of a just hosted on GitHub
+
+USAGE:
+    install [options]
+
+FLAGS:
+    -h, --help      Display this message
+    -f, --force     Force overwriting an existing binary
+
+OPTIONS:
+    --tag TAG       Tag (version) of the crate to install, defaults to latest release
+    --to LOCATION   Where to install the binary [default: ~/.cargo/bin]
+    --target TARGET
+EOF
+}
+
+git=casey/just
+crate=just
+url=https://github.com/casey/just
+releases=$url/releases
+
+say() {
+  echo "install: $@"
+}
+
+say_err() {
+  say "$@" >&2
+}
+
+err() {
+  if [ ! -z ${td-} ]; then
+    rm -rf $td
+  fi
+
+  say_err "error: $@"
+  exit 1
+}
+
+need() {
+  if ! command -v $1 > /dev/null 2>&1; then
+    err "need $1 (command not found)"
+  fi
+}
+
+force=false
+while test $# -gt 0; do
+  case $1 in
+    --force | -f)
+      force=true
+      ;;
+    --help | -h)
+      help
+      exit 0
+      ;;
+    --tag)
+      tag=$2
+      shift
+      ;;
+    --target)
+      target=$2
+      shift
+      ;;
+    --to)
+      dest=$2
+      shift
+      ;;
+    *)
+      ;;
+  esac
+  shift
+done
+
+# Dependencies
+need curl
+need install
+need mkdir
+need mktemp
+need tar
+
+# Optional dependencies
+if [ -z ${tag-} ]; then
+    need grep
+    need cut
+fi
+
+if [ -z ${target-} ]; then
+    need cut
+fi
+
+if [ -z ${dest-} ]; then
+  dest="$HOME/.cargo/bin"
+fi
+
+if [ -z ${tag-} ]; then
+  tag=$(curl --proto =https --tlsv1.2 -sSf https://api.github.com/repos/casey/just/releases/latest |
+    grep tag_name |
+    cut -d'"' -f4
+  )
+fi
+
+if [ -z ${target-} ]; then
+  # bash compiled with MINGW (e.g. git-bash, used in github windows runnners),
+  # unhelpfully includes a version suffix in `uname -s` output, so handle that.
+  # e.g. MINGW64_NT-10-0.19044
+  kernel=$(uname -s | cut -d- -f1)
+  uname_target="`uname -m`-$kernel"
+
+  case $uname_target in
+    aarch64-Linux)     target=aarch64-unknown-linux-musl;;
+    arm64-Darwin)      target=aarch64-apple-darwin;;
+    x86_64-Darwin)     target=x86_64-apple-darwin;;
+    x86_64-Linux)      target=x86_64-unknown-linux-musl;;
+    x86_64-Windows_NT) target=x86_64-pc-windows-msvc;;
+    x86_64-MINGW64_NT) target=x86_64-pc-windows-msvc;;
+    *)
+      err 'Could not determine target from output of `uname -m`-`uname -s`, please use `--target`:' $uname_target
+    ;;
+  esac
+fi
+
+# windows archives are zips, not tarballs
+case $target in
+    x86_64-pc-windows-msvc) extension=zip; need unzip;;
+    *)                      extension=tar.gz;;
+esac
+
+archive="$releases/download/$tag/$crate-$tag-$target.$extension"
+
+say_err "Repository:  $url"
+say_err "Crate:       $crate"
+say_err "Tag:         $tag"
+say_err "Target:      $target"
+say_err "Destination: $dest"
+say_err "Archive:     $archive"
+
+td=$(mktemp -d || mktemp -d -t tmp)
+
+if [ "$extension" = "zip" ]; then
+    # unzip on windows cannot always handle stdin, so download first.
+    curl --proto =https --tlsv1.2 -sSfL $archive > $td/just.zip
+    unzip -d $td $td/just.zip
+else
+    curl --proto =https --tlsv1.2 -sSfL $archive | tar -C $td -xz
+fi
+
+for f in $(ls $td); do
+  test -x $td/$f || continue
+
+  if [ -e "$dest/$f" ] && [ $force = false ]; then
+    err "$f already exists in $dest"
+  else
+    mkdir -p $dest
+    install -m 755 $td/$f $dest
+  fi
+done
+
+rm -rf $td

justfile

@@ -0,0 +1,3 @@
+# test just file
+test:
+   echo ok