Flatten YAML configuration as per review comments

Author: guillaume-d

README.md

@@ -683,21 +683,26 @@ with Overcommit without writing any Ruby code in a similar way as
 
 These special line-aware command hooks behave and are configured the same way
 as the Git ones, except only file arguments get passed to them.
-Also they must have the `ad_hoc` option, so that, using the command output:
+Also to enable the feature, they must use at least one of the following options,
+so that, using the command output:
 - differentiating between warnings and errors becomes possible
 - modified lines can be detected and acted upon as defined by
   the `problem_on_unmodified_line`, `requires_files`, `include` and `exclude`
   [hook options](#hook-options)
 
 **Warning**: Only the command's standard output stream is considered for now,
 *not* its standard error stream.
+If you do not need to change the default values for any other option,
+then the `extract_messages_from` option has to be specified.
+Its value does not matter for now, but it should be set to `stdout`
+to avoid problems in the future.
 
 To differentiate between warning and error messages,
-the `warning_message_type_pattern` suboption may be specified:
+the `warning_message_type_pattern` option may be specified:
 the `type` field of the `message_pattern` regexp below must then include
 the `warning_message_type_pattern` option's text.
 
-The `message_pattern` suboption specifies the format of the command's messages.
+The `message_pattern` option specifies the format of the command's messages.
 It is a optional [(Ruby) regexp][RubyRE], which if present must at least define
 a `file` [named capture group][RubyRENCG].
 The only other allowed ones are `line` and `type`, which when specified
@@ -714,9 +719,8 @@ PreCommit:
   CustomScript:
     enabled: true
     command: './bin/custom-script'
-    ad_hoc:
-      message_pattern: !ruby/regexp /^(?<file>[^:]+):(?<line>[0-9]+):(?<type>[^ ]+)/
-      warning_message_type_pattern: warning
+    message_pattern: !ruby/regexp /^(?<file>[^:]+):(?<line>[0-9]+):(?<type>[^ ]+)/
+    warning_message_type_pattern: warning
 ```
 
 **Tip**: To get the syntax of the regexps right, a Ruby interpreter like `irb`

lib/overcommit/hook_loader/base.rb

@@ -26,21 +26,34 @@ def load_hooks
     AD_HOC_HOOK_DEFAULT_MESSAGE_PATTERN =
       /^(?<file>(?:\w:)?[^:]+):(?<line>\d+):[^ ]* (?<type>[^ ]+)/.freeze
 
-    def create_line_aware_command_hook_class(hook_base)
+    def is_hook_line_aware(hook_config)
+      hook_config['extract_messages_from'] ||
+        hook_config['message_pattern'] ||
+        hook_config['warning_message_type_pattern']
+    end
+
+    def create_line_aware_command_hook_class(hook_base) # rubocop:disable Metrics/MethodLength
       Class.new(hook_base) do
+        def line_aware_config
+          {
+            message_pattern: @config['message_pattern'],
+            warning_message_type_pattern: @config['warning_message_type_pattern']
+          }
+        end
+
         def run
           result = execute(command, args: applicable_files)
 
           return :pass if result.success?
 
-          extract_messages(@config['ad_hoc'], result)
+          extract_messages(line_aware_config, result)
         end
 
-        def extract_messages(ad_hoc_config, result)
-          warning_message_type_pattern = ad_hoc_config['warning_message_type_pattern']
+        def extract_messages(line_aware_config, result)
+          warning_message_type_pattern = line_aware_config[:warning_message_type_pattern]
           Overcommit::Utils::MessagesUtils.extract_messages(
             result.stdout.split("\n"),
-            ad_hoc_config['message_pattern'] ||
+            line_aware_config[:message_pattern] ||
               AD_HOC_HOOK_DEFAULT_MESSAGE_PATTERN,
             Overcommit::Utils::MessagesUtils.create_type_categorizer(
               warning_message_type_pattern

lib/overcommit/hook_loader/plugin_hook_loader.rb

@@ -95,7 +95,7 @@ def create_ad_hoc_hook(hook_name)
 
       hook_config = @config.for_hook(hook_name, @context.hook_class_name)
       hook_class =
-        if hook_config['ad_hoc']
+        if is_hook_line_aware(hook_config)
           create_line_aware_command_hook_class(hook_base)
         else
           create_git_hook_class(hook_base)

spec/overcommit/hook_loader/plugin_hook_loader_spec.rb

@@ -73,24 +73,22 @@
           FooLint:
             enabled: true
             command: ["foo", "lint"]
-            ad_hoc:
-              message_pattern: !ruby/regexp /^(?<file>[^:]+):(?<line>[0-9]+):(?<type>[^ ]+)/
-              warning_message_type_pattern: warning
+            message_pattern: !ruby/regexp /^(?<file>[^:]+):(?<line>[0-9]+):(?<type>[^ ]+)/
+            warning_message_type_pattern: warning
             flags:
             - "--format=emacs"
             include: '**/*.foo'
           FooLintDefault:
             enabled: true
             command: ["foo", "lint"]
-            ad_hoc:
-              warning_message_type_pattern: warning
+            warning_message_type_pattern: warning
             flags:
             - "--format=emacs"
             include: '**/*.foo'
           FooLintDefaultNoWarnings:
             enabled: true
             command: ["foo", "lint"]
-            ad_hoc:
+            extract_messages_from: stdout
             flags:
             - "--format=emacs"
             include: '**/*.foo'