feat: add support for specifying stack builders for builder-cnb

docs/deployment/methods/cloud-native-buildpacks.md

@@ -2,6 +2,9 @@
 
 > New as of 0.22.0
 
+```
+buildpacks:stack-set <app> <stack>           # Sets the stack of an app
+```
 Cloud Native Buildpacks are an evolution over the Buildpacks technology provided by the Herokuish builder. See the [herokuish buildpacks documentation](/docs/deployment/methods/herokuish.md) for more information on how to clear buildpack build cache for an application.
 
 > Warning: This functionality uses the `pack` cli from the [Cloud Native Buildpacks](https://buildpacks.io) project to build apps. As the integration is experimental in Dokku, it is likely to change over time.
@@ -22,10 +25,8 @@ Builds will proceed with the `pack` cli for the app from then on.
 
 As this functionality is highly experimental, there are a number of caveats. Please note that not all issuesare listed below.
 
-- The `heroku/buildpacks:latest` CNB builder is currently enforced. Specifying specific builders is not currently possible.
-  - A future release will allow modifying the chosen builder.
 - Specifying specific buildpacks is not currently possible.
-  - A future release will add support for the `buildpacks` plugin.
+  - A future release will add support for specifying buildpacks via the `buildpacks` plugin.
 - There is currently no way to specify extra arguments for `pack` cli invocations.
   - A future release will add support for injecting extra arguments during the build process.
 - The default process type is `web`.
@@ -33,3 +34,31 @@ As this functionality is highly experimental, there are a number of caveats. Ple
   - A future version will add integration with the `repo` plugin.
 - `pack` is not currently included with Dokku, nor is it added as a package dependency.
   - A future version will include it as a package dependency.
+
+### Customizing the Buildpack stack builder
+
+> New as of 0.23.0
+
+The default stack builder in use by CNB buildpacks in Dokku is based on `heroku/buildpacks`. Users may desire to switch the stack builder to a custom version, either to update the operating system or to customize packages included with the stack builder. This can be performed via the `buildpacks:stack-set` command.
+
+```shell
+dokku buildpacks:stack-set node-js-app paketobuildpacks/build:base-cnb
+```
+
+The specified stack builder can also be unset by omitting the name of the stack builder when calling `buildpacks:stack-set`.
+
+```shell
+dokku buildpacks:stack-set node-js-app
+```
+
+A change in the stack builder value will execute the `post-stack-set` trigger.
+
+Finally, stack builders can be set or unset globally as a fallback. This will take precedence over a globally set `DOKKU_CNB_STACK` environment variable (`heroku/buildpacks` by default).
+
+```shell
+# set globally
+dokku buildpacks:stack-set --global paketobuildpacks/build:base-cnb
+
+# unset globally
+dokku buildpacks:stack-set --global
+```

docs/deployment/methods/herokuish-buildpacks.md

@@ -124,25 +124,25 @@ The `buildpacks:clear` command can be used to clear all configured buildpacks fo
 dokku buildpacks:clear node-js-app
 ```
 
-### Customizing the Buildpack stack
+### Customizing the Buildpack stack builder
 
 > New as of 0.23.0
 
-The default stack in use by Herokuish buildpacks in Dokku is based on `gliderlabs/herokuish`. Typically, this is installed via an OS package which pulls the requisite Docker image. Users may desire to switch the stack to a custom version, either to update the stack operating system or to customize packages included with the stack. This can be performed via teh `buildpacks:stack-set` command.
+The default stack builder in use by Herokuish buildpacks in Dokku is based on `gliderlabs/herokuish:latest`. Typically, this is installed via an OS package which pulls the requisite Docker image. Users may desire to switch the stack builder to a custom version, either to update the operating system or to customize packages included with the stack builder. This can be performed via the `buildpacks:stack-set` command.
 
 ```shell
 dokku buildpacks:stack-set node-js-app gliderlabs/herokuish:latest
 ```
 
-The specified stack can also be unset by omitting the name of the stack when calling `buildpacks:stack-set`.
+The specified stack builder can also be unset by omitting the name of the stack builder when calling `buildpacks:stack-set`.
 
 ```shell
 dokku buildpacks:stack-set node-js-app
 ```
 
-A change in the stack value will execute the `post-stack-set` trigger.
+A change in the stack builder value will execute the `post-stack-set` trigger.
 
-Finally, stacks can be set or unset globally as a fallback. This will take precedence over a globally set `DOKKU_IMAGE` environment variable (`gliderlabs/herokuish:latest` by default).
+Finally, stack builders can be set or unset globally as a fallback. This will take precedence over a globally set `DOKKU_IMAGE` environment variable (`gliderlabs/herokuish:latest` by default).
 
 ```shell
 # set globally

dokku

@@ -42,6 +42,7 @@ DOKKU_DISTRO=$(
 export DOCKER_BIN=${DOCKER_BIN:="docker"}
 
 export DOKKU_IMAGE=${DOKKU_IMAGE:="gliderlabs/herokuish:latest"}
+export DOKKU_CNB_BUILDER=${DOKKU_CNB_BUILDER:="heroku/buildpacks"}
 export DOKKU_LIB_ROOT=${DOKKU_LIB_PATH:="/var/lib/dokku"}
 
 export PLUGIN_PATH=${PLUGIN_PATH:="$DOKKU_LIB_ROOT/plugins"}

plugins/builder-cnb/builder-build

@@ -13,7 +13,13 @@ trigger-builder-cnb-builder-build() {
     return
   fi
 
-  dokku_log_info1 "Building $APP from cnb (experimental)..."
+
+  local stack="$(plugn trigger buildpack-stack-name "$APP")"
+  if [[ -z "$stack" ]]; then
+    DOKKU_CNB_STACK="$stack"
+  fi
+
+  dokku_log_info1 "Building $APP from cnb stack $DOKKU_CNB_STACK (experimental)..."
 
   if ! command -v "pack" &>/dev/null; then
     dokku_log_fail "Missing pack, install it"
@@ -30,7 +36,7 @@ trigger-builder-cnb-builder-build() {
 
   plugn trigger pre-build-cnb "$APP" "$SOURCECODE_WORK_DIR"
 
-  pack build "$IMAGE" --builder heroku/buildpacks --path "$SOURCECODE_WORK_DIR" --default-process web
+  pack build "$IMAGE" --builder "$DOKKU_CNB_BUILDER" --path "$SOURCECODE_WORK_DIR" --default-process web
 
   echo "FROM $IMAGE" | suppress_output "$DOCKER_BIN" image build --label=com.dokku.image-stage=build --label=org.label-schema.schema-version=1.0 --label=org.label-schema.vendor=dokku --label=com.dokku.app-name=$APP --label=dokku -t "$IMAGE" -
 

plugins/builder-herokuish/builder-build

@@ -20,7 +20,6 @@ trigger-builder-herokuish-builder-build() {
     dokku_log_info1 "Building $APP from herokuish"
   fi
 
-
   local IMAGE=$(get_app_image_name "$APP")
   local DOKKU_APP_CACHE_DIR="$DOKKU_ROOT/$APP/cache"
   local DOKKU_APP_HOST_CACHE_DIR="$DOKKU_HOST_ROOT/$APP/cache"