Allow plugins to have a default application path.

This is very handy in Unix world as most applications have standard
installation paths and standard command-line names. Hence, we can now
use those plugins without altering the site.yaml file at all.

hyde/ext/plugins/less.py

@@ -15,6 +15,8 @@ class LessCSSPlugin(CLTransformer):
     The plugin class for less css
     """
 
+    default_app_path = "lessc"
+
     def __init__(self, site):
         super(LessCSSPlugin, self).__init__(site)
 

hyde/ext/plugins/uglify.py

@@ -11,6 +11,8 @@ class UglifyPlugin(CLTransformer):
     The plugin class for Uglify JS
     """
 
+    default_app_path = "uglifyjs"
+
     def __init__(self, site):
         super(UglifyPlugin, self).__init__(site)
 
@@ -68,4 +70,4 @@ class UglifyPlugin(CLTransformer):
 
         self.call_app(args)
         out = target.read_all()
-        return out
+        return out

hyde/plugin.py

@@ -220,6 +220,14 @@ class CLTransformer(Plugin):
 
         return {}
 
+    @property
+    def default_app_path(self):
+        """
+        Default command line application path. Can be overridden
+        by specifying it in config.
+        """
+        return self.plugin_name
+
     @property
     def executable_not_found_message(self):
         """
@@ -253,15 +261,15 @@ class CLTransformer(Plugin):
         try:
             app_path = getattr(self.settings, 'app')
         except AttributeError:
-            raise self.template.exception_class(
-                    self.executable_not_found_message)
+            app_path = self.default_app_path
 
         # Honour the PATH environment variable.
-        if not os.path.isabs(app_path):
+        if app_path is not None and not os.path.isabs(app_path):
             app_path = discover_executable(app_path)
-            if app_path is None:
-                raise self.template.exception_class(
-                        self.executable_not_found_message)
+
+        if app_path is None:
+            raise self.template.exception_class(
+                    self.executable_not_found_message)
 
         app = File(app_path)