Add aliases to Kamal

Aliases are defined in the configuration file under the `aliases` key.

The configuration is a map of alias name to command. When we run the
command the we just do a literal replacement of the alias with the
string.

So if we have:

```yaml
aliases:
  console: app exec -r console -i --reuse "rails console"
```

Then running `kamal console -r workers` will run the command

```sh
$ kamal app exec -r console -i --reuse "rails console" -r workers
```

Because of the order Thor parses the arguments, this allows us to
override the role from the alias command.

There might be cases where we need to munge the command a bit more but
that would involve getting into Thor command parsing internals,
which are complicated and possibly subject to change.

There's a chance that your aliases could conflict with future built-in
commands, but there's not likely to be many of those and if it happens
you'll get a validation error when you upgrade.

Thanks to @dhnaranjo for the idea!

lib/kamal/cli/alias/command.rb

@@ -0,0 +1,9 @@
+class Kamal::Cli::Alias::Command < Thor::DynamicCommand
+  def run(instance, args = [])
+    if (_alias = KAMAL.config.aliases[name])
+      Kamal::Cli::Main.start(Shellwords.split(_alias.command) + ARGV[1..-1])
+    else
+      super
+    end
+  end
+end

lib/kamal/cli/base.rb

@@ -6,7 +6,8 @@ module Kamal::Cli
   class Base < Thor
     include SSHKit::DSL
 
-    def self.exit_on_failure?() true end
+    def self.exit_on_failure?() false end
+    def self.dynamic_command_class() Kamal::Cli::Alias::Command end
 
     class_option :verbose, type: :boolean, aliases: "-v", desc: "Detailed logging"
     class_option :quiet, type: :boolean, aliases: "-q", desc: "Minimal logging"
@@ -22,8 +23,14 @@ module Kamal::Cli
 
     class_option :skip_hooks, aliases: "-H", type: :boolean, default: false, desc: "Don't run hooks"
 
-    def initialize(*)
-      super
+    def initialize(args = [], local_options = {}, config = {})
+      if config[:current_command].is_a?(Kamal::Cli::Alias::Command)
+        # When Thor generates a dynamic command, it doesn't attempt to parse the arguments.
+        # For our purposes, it means the arguments are passed in args rather than local_options.
+        super([], args, config)
+      else
+        super
+      end
       @original_env = ENV.to_h.dup
       load_env
       initialize_commander(options_with_subcommand_class_options)

lib/kamal/commander.rb

@@ -27,7 +27,11 @@ class Kamal::Commander
 
   def specific_primary!
     @specifics = nil
-    self.specific_hosts = [ config.primary_host ]
+    if specific_roles.present?
+      self.specific_hosts = [ specific_roles.first.primary_host ]
+    else
+      self.specific_hosts = [ config.primary_host ]
+    end
   end
 
   def specific_roles=(role_names)
@@ -113,6 +117,10 @@ class Kamal::Commander
     @traefik ||= Kamal::Commands::Traefik.new(config)
   end
 
+  def alias(name)
+    config.aliases[name]
+  end
+
 
   def with_verbosity(level)
     old_level = self.verbosity

lib/kamal/configuration.rb

@@ -11,7 +11,7 @@ class Kamal::Configuration
   delegate :argumentize, :optionize, to: Kamal::Utils
 
   attr_reader :destination, :raw_config
-  attr_reader :accessories, :boot, :builder, :env, :healthcheck, :logging, :traefik, :servers, :ssh, :sshkit, :registry
+  attr_reader :accessories, :aliases, :boot, :builder, :env, :healthcheck, :logging, :traefik, :servers, :ssh, :sshkit, :registry
 
   include Validation
 
@@ -54,6 +54,7 @@ class Kamal::Configuration
     @registry = Registry.new(config: self)
 
     @accessories = @raw_config.accessories&.keys&.collect { |name| Accessory.new(name, config: self) } || []
+    @aliases = @raw_config.aliases&.keys&.to_h { |name| [ name, Alias.new(name, config: self) ] } || {}
     @boot = Boot.new(config: self)
     @builder = Builder.new(config: self)
     @env = Env.new(config: @raw_config.env || {})

lib/kamal/configuration/alias.rb

@@ -0,0 +1,15 @@
+class Kamal::Configuration::Alias
+  include Kamal::Configuration::Validation
+
+  attr_reader :name, :command
+
+  def initialize(name, config:)
+    @name, @command = name.inquiry, config.raw_config["aliases"][name]
+
+    validate! \
+      command,
+      example: validation_yml["aliases"]["uname"],
+      context: "aliases/#{name}",
+      with: Kamal::Configuration::Validator::Alias
+  end
+end

lib/kamal/configuration/docs/alias.yml

@@ -0,0 +1,26 @@
+# Aliases
+#
+# Aliases are shortcuts for Kamal commands.
+#
+# For example, for a Rails app, you might open a console with:
+#
+# ```shell
+# kamal app exec -i -r console "rails console"
+# ```
+#
+# By defining an alias, like this:
+aliases:
+  console: app exec -r console -i "rails console"
+# You can now open the console with:
+# ```shell
+# kamal console
+# ```
+
+# Configuring aliases
+#
+# Aliases are defined in the root config under the alias key
+#
+# Each alias is named and can only contain lowercase letters, numbers, dashes and underscores.
+
+aliases:
+  uname: app exec -p -q -r web "uname -a"

lib/kamal/configuration/docs/configuration.yml

@@ -166,3 +166,9 @@ healthcheck:
 # Docker logging configuration, see kamal docs logging
 logging:
   ...
+
+# Aliases
+#
+# Alias configuration, see kamal docs alias
+aliases:
+  ...

lib/kamal/configuration/validator.rb

@@ -13,32 +13,34 @@ class Kamal::Configuration::Validator
 
   private
     def validate_against_example!(validation_config, example)
-      validate_type! validation_config, Hash
+      validate_type! validation_config, example.class
 
-      check_unknown_keys! validation_config, example
+      if example.class == Hash
+        check_unknown_keys! validation_config, example
 
-      validation_config.each do |key, value|
-        next if extension?(key)
-        with_context(key) do
-          example_value = example[key]
+        validation_config.each do |key, value|
+          next if extension?(key)
+          with_context(key) do
+            example_value = example[key]
 
-          if example_value == "..."
-            validate_type! value, *(Array if key == :servers), Hash
-          elsif key == "hosts"
-            validate_servers! value
-          elsif example_value.is_a?(Array)
-            validate_array_of! value, example_value.first.class
-          elsif example_value.is_a?(Hash)
-            case key.to_s
-            when "options", "args"
-              validate_type! value, Hash
-            when "labels"
-              validate_hash_of! value, example_value.first[1].class
+            if example_value == "..."
+              validate_type! value, *(Array if key == :servers), Hash
+            elsif key == "hosts"
+              validate_servers! value
+            elsif example_value.is_a?(Array)
+              validate_array_of! value, example_value.first.class
+            elsif example_value.is_a?(Hash)
+              case key.to_s
+              when "options", "args"
+                validate_type! value, Hash
+              when "labels"
+                validate_hash_of! value, example_value.first[1].class
+              else
+                validate_against_example! value, example_value
+              end
             else
-              validate_against_example! value, example_value
+              validate_type! value, example_value.class
             end
-          else
-            validate_type! value, example_value.class
           end
         end
       end

lib/kamal/configuration/validator/alias.rb

@@ -0,0 +1,15 @@
+class Kamal::Configuration::Validator::Alias < Kamal::Configuration::Validator
+  def validate!
+    super
+
+    name = context.delete_prefix("aliases/")
+
+    if name !~ /\A[a-z0-9_-]+\z/
+      error "Invalid alias name: '#{name}'. Must only contain lowercase letters, alphanumeric, hyphens and underscores."
+    end
+
+    if Kamal::Cli::Main.commands.include?(name)
+      error "Alias '#{name}' conflicts with a built-in command."
+    end
+  end
+end