Escape strings for the shell

Whitespaces in strings were interpreted by the shell as new words.
Escaping them ensures the shell sees the string as a single value.

lib/kamal/commands/builder/base.rb

@@ -1,3 +1,5 @@
+require "shellwords"
+
 class Kamal::Commands::Builder::Base < Kamal::Commands::Base
   class BuilderError < StandardError; end
 
@@ -44,7 +46,7 @@ class Kamal::Commands::Builder::Base < Kamal::Commands::Base
   end
 
   def build_context
-    config.builder.context
+    Shellwords.escape(config.builder.context)
   end
 
   def validate_image
@@ -92,7 +94,7 @@ class Kamal::Commands::Builder::Base < Kamal::Commands::Base
 
     def build_dockerfile
       if Pathname.new(File.expand_path(dockerfile)).exist?
-        argumentize "--file", dockerfile
+        argumentize "--file", Shellwords.escape(dockerfile)
       else
         raise BuilderError, "Missing #{dockerfile}"
       end

lib/kamal/docker.rb

@@ -1,5 +1,6 @@
 require "tempfile"
 require "open3"
+require "shellwords"
 
 module Kamal::Docker
   extend self
@@ -15,7 +16,7 @@ module Kamal::Docker
       DOCKERFILE
       dockerfile.close
 
-      cmd = "docker buildx build -t=#{BUILD_CHECK_TAG} -f=#{dockerfile.path} ."
+      cmd = "docker buildx build -t=#{BUILD_CHECK_TAG} -f=#{Shellwords.escape(dockerfile.path)} ."
       system(cmd) || raise("failed to build check image")
     end