feat: add support for nixpacks as a builder

Closes #5338

tests/unit/builder-nixpacks.bats

@@ -0,0 +1,52 @@
+#!/usr/bin/env bats
+
+load test_helper
+
+setup_file() {
+  install_nixpacks
+}
+
+setup() {
+  create_app
+}
+
+teardown() {
+  destroy_app
+}
+
+@test "(builder-nixpacks: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 nixpacks"
+  echo "output: $output"
+  echo "status: $status"
+  assert_success
+
+  run deploy_app python dokku@dokku.me:$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-nixpacks:set $TEST_APP nixpackstoml-path nonexistent.toml"
+  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/test_helper.bash

@@ -601,6 +601,13 @@ detach_delete_network() {
   delete_network "$NETWORK_NAME"
 }
 
+convert_to_dockerfile() {
+  local APP="$1"
+  local APP_REPO_DIR="$2"
+  [[ -z "$APP" ]] && local APP="$TEST_APP"
+  mv "$APP_REPO_DIR/dockerfile.Dockerfile" "$APP_REPO_DIR/Dockerfile"
+}
+
 install_pack() {
   if ! command -v "pack" &>/dev/null; then
     add-apt-repository --yes ppa:cncf-buildpacks/pack-cli
@@ -609,9 +616,8 @@ install_pack() {
   fi
 }
 
-convert_to_dockerfile() {
-  local APP="$1"
-  local APP_REPO_DIR="$2"
-  [[ -z "$APP" ]] && local APP="$TEST_APP"
-  mv "$APP_REPO_DIR/dockerfile.Dockerfile" "$APP_REPO_DIR/Dockerfile"
+install_nixpacks() {
+  if ! command -v "nixpacks" &>/dev/null; then
+    curl -sSL https://nixpacks.com/install.sh | FORCE=1 bash
+  fi
 }