(GH-1350) Allow plugin_hooks to contain references

Previously, the value of `plugin_hooks` had to be static with all
hooks and parameters being defined in the config file. We now allow
these hooks and parameters to be looked up using plugins, which is
helpful if an external source is responsible for controlling the Puppet
version to use or if the Puppet install method requires the knowledge of
some secret.

Author: nicklewis

documentation/bolt_configuration_options.md

@@ -232,3 +232,14 @@ plugin_hooks:
       master: 'puppet.example.com'
       cacert_content: <CERT>
 ```
+
+You can also configure `plugin_hooks` using `_plugin` references:
+
+```yaml
+plugin_hooks:
+  puppet_library:
+    plugin: puppet_agent
+    version:
+      _plugin: prompt
+      message: "Which version of Puppet do you want to install?"
+```

lib/bolt/inventory.rb

@@ -234,7 +234,7 @@ def update_target(target)
       set_facts(target.name, data['facts']) unless @target_facts[target.name]
       data['features']&.each { |feature| set_feature(target, feature) } unless @target_features[target.name]
       unless @target_plugin_hooks[target.name]
-        set_plugin_hooks(target.name, @config.plugin_hooks.merge(data['plugin_hooks'] || {}))
+        set_plugin_hooks(target.name, (@plugins&.default_plugin_hooks || {}).merge(data['plugin_hooks'] || {}))
       end
 
       # Use Config object to ensure config section is treated consistently with config file

lib/bolt/inventory/target.rb

@@ -80,7 +80,7 @@ def set_feature(feature, value = true)
       def plugin_hooks
         # Merge plugin_hooks from the config file with any defined by the group
         # or assigned dynamically to the target
-        @inventory.config.plugin_hooks.merge(group_cache['plugin_hooks']).merge(@plugin_hooks)
+        @inventory.plugins.default_plugin_hooks.merge(group_cache['plugin_hooks']).merge(@plugin_hooks)
       end
 
       def set_config(key_or_key_path, value)

lib/bolt/plugin.rb

@@ -39,9 +39,10 @@ def initialize(plugin_name, hook)
     end
 
     class PluginContext
-      def initialize(config, pal)
+      def initialize(config, pal, plugins)
         @pal = pal
         @config = config
+        @plugins = plugins
       end
 
       def serial_executor
@@ -50,7 +51,7 @@ def serial_executor
       private :serial_executor
 
       def empty_inventory
-        @empty_inventory ||= Bolt::Inventory.new({}, @config)
+        @empty_inventory ||= Bolt::Inventory::Inventory2.new({}, @config, plugins: @plugins)
       end
       private :empty_inventory
 
@@ -131,25 +132,29 @@ def self.setup(config, pal, pdb_client, analytics)
         plugins.by_name(plugin)
       end
 
+      plugins.default_plugin_hooks = plugins.resolve_references(config.plugin_hooks)
+
       plugins
     end
 
     RUBY_PLUGINS = %w[install_agent task pkcs7 prompt].freeze
     BUILTIN_PLUGINS = %w[task terraform pkcs7 prompt vault aws_inventory puppetdb azure_inventory].freeze
 
     attr_reader :pal, :plugin_context
+    attr_accessor :default_plugin_hooks
 
     private_class_method :new
 
     def initialize(config, pal, analytics)
       @config = config
       @analytics = analytics
-      @plugin_context = PluginContext.new(config, pal)
+      @plugin_context = PluginContext.new(config, pal, self)
       @plugins = {}
       @pal = pal
       @unknown = Set.new
       @resolution_stack = []
       @unresolved_plugin_configs = config.plugins.dup
+      @default_plugin_hooks = {}
     end
 
     def modules

spec/bolt/inventory_spec.rb

@@ -759,7 +759,7 @@ def common_data(transport)
       }] }
     }
 
-    let(:inventory) { Bolt::Inventory.new(data) }
+    let(:inventory) { Bolt::Inventory.new(data, plugins: plugins) }
     let(:target) { get_target(inventory, 'foo') }
     let(:expected_data) {
       { 'name' => 'foo',

spec/bolt/plugin_spec.rb

@@ -61,4 +61,16 @@ def identity(value)
       expect { plugins }.to raise_error(/Configuration for plugin 'pkcs7' depends on the plugin itself/)
     end
   end
+
+  context 'loading plugin_hooks' do
+    it 'evaluates plugin references in the plugin_hooks configuration' do
+      config_data['plugin_hooks'] = {
+        'puppet_library' => {
+          'plugin' => 'my_hook',
+          'param' => identity('foobar')
+        }
+      }
+      expect(plugins.default_plugin_hooks['puppet_library']).to eq('plugin' => 'my_hook', 'param' => 'foobar')
+    end
+  end
 end