Reviewers: mp+171779_code.launchpad.net,

Message:
Please take a look.

Description:
charm: allow empty string as default value

The current solution is incompatible to pyjuju,
where empty strings as default values are allowed.
Added this as an exceptional case to the charm
config.

https://code.launchpad.net/~themue/juju-core/032-config-default-empty-string/+merge/171779

(do not edit description out of merge proposal)


Please review this at https://codereview.appspot.com/10682043/

Affected files:
   A [revision details]
   M charm/config.go
   M charm/config_test.go


Index: [revision details]
=== added file '[revision details]'
--- [revision details]	2012-01-01 00:00:00 +0000
+++ [revision details]	2012-01-01 00:00:00 +0000
@@ -0,0 +1,2 @@
+Old revision: tarmac-20130627084404-bq6fxhiknqub7hna
+New revision: <email address hidden>

Index: charm/config.go
=== modified file 'charm/config.go'
--- charm/config.go	2013-06-11 14:55:46 +0000
+++ charm/config.go	2013-06-27 11:50:08 +0000
@@ -110,10 +110,13 @@
  		default:
  			return nil, fmt.Errorf("invalid config: option %q has unknown type %q",  
name, option.Type)
  		}
-		def := option.Default
-		if option.Default, err = option.validate(name, def); err != nil {
-			option.error(&err, name, def)
-			return nil, fmt.Errorf("invalid config default: %v", err)
+		if !(option.Type == "string" && option.Default == "") {
+			// Empty default string is an exceptional case due to compatability  
reasons.
+			def := option.Default
+			if option.Default, err = option.validate(name, def); err != nil {
+				option.error(&err, name, def)
+				return nil, fmt.Errorf("invalid config default: %v", err)
+			}
  		}
  		config.Options[name] = option
  	}


Index: charm/config_test.go
=== modified file 'charm/config_test.go'
--- charm/config_test.go	2013-06-17 13:12:56 +0000
+++ charm/config_test.go	2013-06-27 11:50:08 +0000
@@ -26,6 +26,9 @@
      default: My Title
      description: A descriptive title used for the service.
      type: string
+  subtitle:
+    default: ""
+    description: An optional subtitle used for the service.
    outlook:
      description: No default outlook.
      # type defaults to string in python
@@ -53,6 +56,11 @@
  			Description: "A descriptive title used for the service.",
  			Type:        "string",
  		},
+		"subtitle": {
+			Default:     "",
+			Description: "An optional subtitle used for the service.",
+			Type:        "string",
+		},
  		"username": {
  			Default:     "admin001",
  			Description: "The name of the initial account (given admin  
permissions).",
@@ -80,6 +88,7 @@
  func (s *ConfigSuite) TestDefaultSettings(c *C) {
  	c.Assert(s.config.DefaultSettings(), DeepEquals, charm.Settings{
  		"title":              "My Title",
+		"subtitle":           "",
  		"username":           "admin001",
  		"outlook":            nil,
  		"skill-level":        nil,
@@ -91,6 +100,7 @@
  func (s *ConfigSuite) TestFilterSettings(c *C) {
  	settings := s.config.FilterSettings(charm.Settings{
  		"title":              "something valid",
+		"subtitle":           "",
  		"username":           nil,
  		"unknown":            "whatever",
  		"outlook":            "",
@@ -100,6 +110,7 @@
  	})
  	c.Assert(settings, DeepEquals, charm.Settings{
  		"title":    "something valid",
+		"subtitle": nil,
  		"username": nil,
  		"outlook":  nil,
  	})
@@ -376,6 +387,7 @@

  	assertDefault("boolean", "true", true)
  	assertDefault("string", "golden grahams", "golden grahams")
+	assertDefault("string", `""`, "")
  	assertDefault("float", "2.2e11", 2.2e11)
  	assertDefault("int", "99", int64(99))