Updated README instruction

.github/workflows/buildpack-bun.yml

@@ -0,0 +1,13 @@
+name: buildpack-bun
+
+on: push
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Run Buildpack Compile
+      run:  ./bin/compile . . .

README.md

@@ -2,8 +2,15 @@
 
 Heroku buildpack for Bun.js
 
-Largely copied from https://github.com/chibat/heroku-buildpack-deno
+You can optionally control the specific version by setting the `BUN_VERSION` environment-level variable to an explicit version e.g. 1.0.16
+<img width="956" alt="Screenshot 2024-01-09 at 3 16 03 pm" src="https://github.com/callumfrance/heroku-buildpack-bun/assets/13757101/257737dc-7f04-4fae-9cc5-30ed69b30aa6">
 
-Pin a certain Bun version with a `runtime.bun.txt` or `runtime.txt` with e.g. `v0.5.9` in it.
+## How do I use this?
+This is a third party heroku buildpack, so you will need to follow [the instructions provided by Heroku](https://devcenter.heroku.com/articles/buildpacks#using-a-third-party-buildpack) to enable it for your app.
+You will need to assign the buildpack via the `heroku buildpacks:set` command.
 
-Be aware that Heroku doesn't use a new enough version of the Linux kernel to support `io_uring`, which is needed for `Bun.write()`. Use `node:fs.writeFile()` instead.
+If your app's entrypoint is at `src/index.ts`, here's an example `Procfile` you could potentially use:
+
+```Procfile
+web: bun install --frozen-lockfile && bun src/index.ts
+```

bin/compile

@@ -2,20 +2,48 @@
 # bin/compile <build-dir> <cache-dir> <env-dir>
 # $HOME: /app
 
-set -e
+set -o errexit
+set -o pipefail
+set -o nounset
+unset GIT_DIR
+
+function topic() {
+    echo "-----> $*..."
+}
+
+function indent() {
+    c='s/^/       /'
+    case $(uname) in
+    Darwin) sed -l "$c" ;;
+    *) sed -u "$c" ;;
+    esac
+}
 
 BUILD_DIR=${1:-.}
 CACHE_DIR=${2:-}
 ENV_DIR=${3:-}
 
+# determine version to install
+if [ -f $ENV_DIR/BUN_VERSION ]; then
+    PROVIDED_VERSION_NUMBER=$(cat $ENV_DIR/BUN_VERSION)
+    VERSION="-s bun-v$PROVIDED_VERSION_NUMBER"
+    topic "Using bun v${PROVIDED_VERSION_NUMBER} (set by the env var 'BUN_VERSION')"
+else
+    VERSION=""
+    topic "Defaulting to latest version of bun"
+fi
+indent "Version $VERSION"
+
 # install bun
 export BUN_INSTALL=$BUILD_DIR/.bun
-curl -fsSL https://bun.sh/install | bash
+curl -fsSL https://bun.sh/install | bash $VERSION
 
 # set environment variables
 export PATH=$BUN_INSTALL/bin:$PATH
 PROFILE_PATH="$BUILD_DIR/.profile.d/bun.sh"
 mkdir -p $(dirname $PROFILE_PATH)
-echo 'export PATH="$HOME/.bun/bin:$PATH"' >> $PROFILE_PATH
+echo 'export PATH="$HOME/.bun/bin:$PATH"' >>$PROFILE_PATH
+
+bun --version
 
-set +e
+indent "Created"