feat: add a Railpack builder to Dokku

Closes #7615

tests/unit/builder-railpack.bats

@@ -0,0 +1,52 @@
+#!/usr/bin/env bats
+
+load test_helper
+
+setup_file() {
+  install_railpack
+}
+
+setup() {
+  create_app
+}
+
+teardown() {
+  destroy_app
+}
+
+@test "(builder-railpack:set)" {
+  run /bin/bash -c "dokku config:set $TEST_APP SECRET_KEY=fjdkslafjdk"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run /bin/bash -c "dokku builder:set $TEST_APP selected railpack"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run deploy_app python dokku@$DOKKU_DOMAIN:$TEST_APP inject_requirements_txt
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+  assert_output_contains 'load build definition from Dockerfile'
+  assert_output_contains "SECRET_KEY: fjdkslafjdk"
+
+  run /bin/bash -c "dokku builder-railpack:set $TEST_APP railpackjson-path nonexistent.json"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run /bin/bash -c "dokku ps:rebuild $TEST_APP"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+  assert_output_contains 'load build definition from Dockerfile'
+}
+
+inject_requirements_txt() {
+  local APP="$1"
+  local APP_REPO_DIR="$2"
+  [[ -z "$APP" ]] && local APP="$TEST_APP"
+  echo "flask" >>"$APP_REPO_DIR/requirements.txt"
+}

tests/unit/report.bats

@@ -103,6 +103,7 @@ teardown() {
     builder-herokuish
     builder-lambda
     builder-nixpacks
+    builder-railpack
     builder-pack
     buildpacks
     caddy

tests/unit/test_helper.bash

@@ -660,6 +660,12 @@ install_nixpacks() {
   fi
 }
 
+install_railpack() {
+  if ! command -v "railpack" &>/dev/null; then
+    curl -sSL https://railpack.com/install.sh | FORCE=1 bash
+  fi
+}
+
 install_k3s() {
   run /bin/bash -c "dokku proxy:set --global k3s"
   echo "output: $output"