feat: Introduce a build dev command

which will build a "dirty" image using the working directory.

This command is different from `build push` in two important ways:

- the image tags will have a suffix of `-dirty`
- the export action is "docker", pushing to the local docker image store

The command also supports the `--output` option just added to `build
push` to override that default.

This command is intended to allow developers to quickly iterate on a
docker image built from their local working directory while avoiding
any confusion with a pristine image built from a git clone, and
keeping those images on the local dev system by default.

lib/kamal/cli/build.rb

@@ -109,6 +109,28 @@ def details
     end
   end
 
+  desc "dev", "Build using the working directory, tag it as dirty, and push to local image store."
+  option :output, type: :string, default: "docker", banner: "export_type", desc: "Exported type for the build result, and may be any exported type supported by 'buildx --output'."
+  def dev
+    cli = self
+
+    ensure_docker_installed
+
+    uncommitted_changes = Kamal::Git.uncommitted_changes
+    if uncommitted_changes.present?
+      say "WARNING: building with uncommitted changes:\n #{uncommitted_changes}", :yellow
+    end
+
+    with_env(KAMAL.config.builder.secrets) do
+      run_locally do
+        build = KAMAL.builder.push(cli.options[:output], tag_as_dirty: true)
+        KAMAL.with_verbosity(:debug) do
+          execute(*build)
+        end
+      end
+    end
+  end
+
   private
     def connect_to_remote_host(remote_host)
       remote_uri = URI.parse(remote_host)

lib/kamal/commands/builder.rb

@@ -1,7 +1,7 @@
 require "active_support/core_ext/string/filters"
 
 class Kamal::Commands::Builder < Kamal::Commands::Base
-  delegate :create, :remove, :push, :clean, :pull, :info, :inspect_builder, :validate_image, :first_mirror, to: :target
+  delegate :create, :remove, :dev, :push, :clean, :pull, :info, :inspect_builder, :validate_image, :first_mirror, to: :target
   delegate :local?, :remote?, :cloud?, to: "config.builder"
 
   include Clone

lib/kamal/commands/builder/base.rb

@@ -13,11 +13,12 @@ def clean
     docker :image, :rm, "--force", config.absolute_image
   end
 
-  def push(export_action = "registry")
+  def push(export_action = "registry", tag_as_dirty: false)
     docker :buildx, :build,
       "--output=type=#{export_action}",
       *platform_options(arches),
       *([ "--builder", builder_name ] unless docker_driver?),
+      *build_tag_options(tag_as_dirty: tag_as_dirty),
       *build_options,
       build_context
   end
@@ -37,7 +38,7 @@ def inspect_builder
   end
 
   def build_options
-    [ *build_tags, *build_cache, *build_labels, *build_args, *build_secrets, *build_dockerfile, *build_target, *build_ssh, *builder_provenance, *builder_sbom ]
+    [ *build_cache, *build_labels, *build_args, *build_secrets, *build_dockerfile, *build_target, *build_ssh, *builder_provenance, *builder_sbom ]
   end
 
   def build_context
@@ -58,8 +59,14 @@ def first_mirror
   end
 
   private
-    def build_tags
-      [ "-t", config.absolute_image, "-t", config.latest_image ]
+    def build_tag_names(tag_as_dirty: false)
+      tag_names = [ config.absolute_image, config.latest_image ]
+      tag_names.map! { |t| "#{t}-dirty" } if tag_as_dirty
+      tag_names
+    end
+
+    def build_tag_options(tag_as_dirty: false)
+      build_tag_names(tag_as_dirty: tag_as_dirty).flat_map { |name| [ "-t", name ] }
     end
 
     def build_cache

test/cli/build_test.rb

@@ -298,6 +298,30 @@ class CliBuildTest < CliTestCase
     end
   end
 
+  test "dev" do
+    with_build_directory do |build_directory|
+      Kamal::Commands::Hook.any_instance.stubs(:hook_exists?).returns(true)
+
+      run_command("dev", "--verbose").tap do |output|
+        assert_no_match(/Cloning repo into build directory/, output)
+        assert_match(/docker --version && docker buildx version/, output)
+        assert_match(/docker buildx build --output=type=docker --platform linux\/amd64 --builder kamal-local-docker-container -t dhh\/app:999-dirty -t dhh\/app:latest-dirty --label service="app" --file Dockerfile \. as .*@localhost/, output)
+      end
+    end
+  end
+
+  test "dev --output=local" do
+    with_build_directory do |build_directory|
+      Kamal::Commands::Hook.any_instance.stubs(:hook_exists?).returns(true)
+
+      run_command("dev", "--output=local", "--verbose").tap do |output|
+        assert_no_match(/Cloning repo into build directory/, output)
+        assert_match(/docker --version && docker buildx version/, output)
+        assert_match(/docker buildx build --output=type=local --platform linux\/amd64 --builder kamal-local-docker-container -t dhh\/app:999-dirty -t dhh\/app:latest-dirty --label service="app" --file Dockerfile \. as .*@localhost/, output)
+      end
+    end
+  end
+
   private
     def run_command(*command, fixture: :with_accessories)
       stdouted { Kamal::Cli::Build.start([ *command, "-c", "test/fixtures/deploy_#{fixture}.yml" ]) }