allow alternative URIs for flox installable (#18)

Co-authored-by: Zach Mitchell, PhD <zmitchell@fastmail.com>

.github/workflows/test-prerelease.yml

@@ -0,0 +1,21 @@
+name: "install-flox-action test pre-release"
+on:
+  workflow_dispatch:
+  pull_request:
+  push:
+    branches:
+      - "main"
+
+jobs:
+  install-flox-pre-release:
+    strategy:
+      matrix:
+        os: ["ubuntu-latest"] # macos not yet populated
+    runs-on: "${{ matrix.os }}"
+    steps:
+      - uses: "actions/checkout@v3"
+      - name: "Install flox pre-release"
+        uses: "./"
+        with:
+          cache-key: "install-flox-action-test"
+          flox-installable-uri: "github:flox/floxpkgs#flox-prerelease.fromCatalog"

README.md

@@ -126,6 +126,42 @@ jobs:
         flox nix copy --to "$FLOX_SUBSTITUTER" -v nixpkgs#hello
 ```
 
+## Use an alternative `flox` executable
+
+You can override the default (latest stable release) executable for `flox`
+by providing explicit URIs for either an alternative `floxpkgs` 
+[flake](https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-flake.html#url-like-syntax)
+or `flox`
+[installable URI](https://nixos.org/manual/nix/stable/command-ref/new-cli/nix.html#installables).
+
+For example to use `flox` from a particular `floxpkgs` revision you could set
+
+```yml
+# ...<SNIP>...
+jobs:
+# ...<SNIP>...
+    - name: Install flox
+      uses: flox/install-flox-action@v1
+      with:
+        floxpkgs-uri: "github:flox/floxpkgs/7df34f186e0a93cc45f8d08c85705c2e18f2ef10"
+```
+
+Alternatively you can provide an installable URI for an alternative `flox`
+package (useful for working on development builds) with the following:
+
+```yml
+# ...<SNIP>...
+jobs:
+# ...<SNIP>...
+    - name: Install flox
+      uses: flox/install-flox-action@v1
+      with:
+        # For a local checkout:
+        flox-installable-uri: ".#flox"
+        # For the pre-release:
+        #flox-installable-uri: "github:flox/floxpkgs#flox-prerelease.fromCatalog"
+```
+
 ## 📫 Have a question? Want to chat? Ran into a problem?
 
 We are happy to welcome you to our [Discourse forum][discourse] and answer your

action.yml

@@ -31,6 +31,17 @@ inputs:
     description: "AWS access key to upload"
   aws-secret-access-key:
     description: "AWS secret key to upload"
+  floxpkgs-uri:
+    description: |
+      URI to use when resolving `flox` executable.
+      Ignored if `flox-installable-uri` is given.
+    default: "github:flox/floxpkgs"
+  flox-installable-uri:
+    required: false
+    description: |
+      Absolute installable URI to `flox` executable.
+      Takes precedence over `floxpkgs-uri` setting.
+
 
 runs:
   using: "composite"
@@ -74,6 +85,9 @@ runs:
 
     - name: "Install flox"
       shell: "bash"
+      env:
+        FLOXPKGS_URI: "${{ inputs.floxpkgs-uri }}"
+        FLOX_INSTALLABLE_URI: "${{ inputs.flox-installable-uri }}"
       run: "${{ github.action_path }}/install-flox.sh"
 
     - name: "Setup substituter"

install-flox.sh

@@ -2,20 +2,25 @@
 set -euo pipefail
 
 if ! type -p nix &>/dev/null ; then
-  echo "Aborting: Nix is not installed, please configure nix using https://github.com/marketplace/actions/install-nix"
+  printf '%s' "Aborting: Nix is not installed, please configure nix using "  \
+              "https://github.com/marketplace/actions/install-nix"
   exit
 fi
 
-# GitHub command to put the following log messages into a group which is collapsed by default
+# GitHub command to put the following log messages into a group which is
+# collapsed by default
 echo "::group::Installing Flox"
 
+: "${FLOXPKGS_URI:=github:flox/floxpkgs}"
+: "${FLOX_INSTALLABLE_URI:=$FLOXPKGS_URI#flox.fromCatalog}"
+
 nix profile install --impure \
       --experimental-features "nix-command flakes" \
       --accept-flake-config \
-      'github:flox/floxpkgs#flox.fromCatalog'
+      "$FLOX_INSTALLABLE_URI"
 
 # Check it runs
-$HOME/.nix-profile/bin/flox --version
+"$HOME/.nix-profile/bin/flox" --version
 
 # This might already be set e.g. if Nix was installed using install-nix-action.
 # If Nix was already installed through other means (e.g. on a hosted runner)