Handle corrupt git clones

When cloning the git repo:
1. Try to clone
2. If there's already a build directory reset it
3. Check the clone is valid

If anything goes wrong during that process:
1. Delete the clone directory
2. Clone it again
3. Check the clone is valid

Raise any errors after that

lib/kamal/cli/build.rb

@@ -23,7 +23,9 @@ class Kamal::Cli::Build < Kamal::Cli::Base
         say "Building from a local git clone, so ignoring these uncommitted changes:\n #{uncommitted_changes}", :yellow
       end
 
-      prepare_clone
+      run_locally do
+        Clone.new(self).prepare
+      end
     elsif uncommitted_changes.present?
       say "Building with uncommitted changes:\n #{uncommitted_changes}", :yellow
     end
@@ -126,23 +128,4 @@ class Kamal::Cli::Build < Kamal::Cli::Base
         end
       end
     end
-
-    def prepare_clone
-      run_locally do
-        begin
-          info "Cloning repo into build directory `#{KAMAL.config.builder.build_directory}`..."
-
-          execute *KAMAL.builder.create_clone_directory
-          execute *KAMAL.builder.clone
-        rescue SSHKit::Command::Failed => e
-          if e.message =~ /already exists and is not an empty directory/
-            info "Resetting local clone as `#{KAMAL.config.builder.build_directory}` already exists..."
-
-            KAMAL.builder.clone_reset_steps.each { |step| execute *step }
-          else
-            raise
-          end
-        end
-      end
-    end
 end

lib/kamal/cli/build/clone.rb

@@ -0,0 +1,61 @@
+require "uri"
+
+class Kamal::Cli::Build::Clone
+  attr_reader :sshkit
+  delegate :info, :error, :execute, :capture_with_info, to: :sshkit
+
+  def initialize(sshkit)
+    @sshkit = sshkit
+  end
+
+  def prepare
+    begin
+      clone_repo
+    rescue SSHKit::Command::Failed => e
+      if e.message =~ /already exists and is not an empty directory/
+        reset
+      else
+        raise Kamal::Cli::Build::BuildError, "Failed to clone repo: #{e.message}"
+      end
+    end
+
+    validate!
+  rescue Kamal::Cli::Build::BuildError => e
+    error "Error preparing clone: #{e.message}, deleting and retrying..."
+
+    FileUtils.rm_rf KAMAL.config.builder.clone_directory
+    clone_repo
+    validate!
+  end
+
+  private
+    def clone_repo
+      info "Cloning repo into build directory `#{KAMAL.config.builder.build_directory}`..."
+
+      FileUtils.mkdir_p KAMAL.config.builder.clone_directory
+      execute *KAMAL.builder.clone
+    end
+
+    def reset
+      info "Resetting local clone as `#{KAMAL.config.builder.build_directory}` already exists..."
+
+      KAMAL.builder.clone_reset_steps.each { |step| execute *step }
+    rescue SSHKit::Command::Failed => e
+      raise Kamal::Cli::Build::BuildError, "Failed to clone repo: #{e.message}"
+    end
+
+    def validate!
+      status = capture_with_info(*KAMAL.builder.clone_status).strip
+
+      unless status.empty?
+        raise Kamal::Cli::Build::BuildError, "Clone in #{KAMAL.config.builder.build_directory} is dirty, #{status}"
+      end
+
+      revision = capture_with_info(*KAMAL.builder.clone_revision).strip
+      if revision != Kamal::Git.revision
+        raise Kamal::Cli::Build::BuildError, "Clone in #{KAMAL.config.builder.build_directory} is not on the correct revision, expected `#{Kamal::Git.revision}` but got `#{revision}`"
+      end
+    rescue SSHKit::Command::Failed => e
+      raise Kamal::Cli::Build::BuildError, "Failed to validate clone: #{e.message}"
+    end
+end

lib/kamal/commands/builder.rb

@@ -2,7 +2,8 @@ require "active_support/core_ext/string/filters"
 
 class Kamal::Commands::Builder < Kamal::Commands::Base
   delegate :create, :remove, :push, :clean, :pull, :info, :validate_image, to: :target
-  delegate :clone_directory, :build_directory, to: :"config.builder"
+
+  include Clone
 
   def name
     target.class.to_s.remove("Kamal::Commands::Builder::").underscore.inquiry
@@ -54,23 +55,6 @@ class Kamal::Commands::Builder < Kamal::Commands::Base
     end
   end
 
-  def create_clone_directory
-    make_directory clone_directory
-  end
-
-  def clone
-    git :clone, Kamal::Git.root, path: clone_directory
-  end
-
-  def clone_reset_steps
-    [
-      git(:remote, "set-url", :origin, Kamal::Git.root, path: build_directory),
-      git(:fetch, :origin, path: build_directory),
-      git(:reset, "--hard", Kamal::Git.revision, path: build_directory),
-      git(:clean, "-fdx", path: build_directory)
-    ]
-  end
-
   private
     def ensure_local_docker_installed
       docker "--version"

lib/kamal/commands/builder/clone.rb

@@ -0,0 +1,28 @@
+module Kamal::Commands::Builder::Clone
+  extend ActiveSupport::Concern
+
+  included do
+    delegate :clone_directory, :build_directory, to: :"config.builder"
+  end
+
+  def clone
+    git :clone, Kamal::Git.root, path: clone_directory
+  end
+
+  def clone_reset_steps
+    [
+      git(:remote, "set-url", :origin, Kamal::Git.root, path: build_directory),
+      git(:fetch, :origin, path: build_directory),
+      git(:reset, "--hard", Kamal::Git.revision, path: build_directory),
+      git(:clean, "-fdx", path: build_directory)
+    ]
+  end
+
+  def clone_status
+    git :status, "--porcelain", path: build_directory
+  end
+
+  def clone_revision
+    git :"rev-parse", :HEAD, path: build_directory
+  end
+end