Fix the code and update tests that verify the new code works

Signed-off-by: Milos Gajdos <milosthegajdos@gmail.com>

configuration/parser.go

@@ -172,10 +172,18 @@ func (p *Parser) overwriteFields(v reflect.Value, fullpath string, path []string
 			panic("non-numeric index: " + path[0])
 		}
 
-		if idx >= v.Len() {
+		if idx > v.Len() {
-			panic("Undefined index: " + path[0])
+			panic("undefined index: " + path[0])
 		}
 
+		// if there is no element or the current slice length
+		// is the same as the indexed variable create a new element,
+		// append it and then set it to the passed in env var value.
+		if v.Len() == 0 || idx == v.Len() {
+			typ := v.Type().Elem()
+			elem := reflect.New(typ).Elem()
+			v.Set(reflect.Append(v, elem))
+		}
 		return p.overwriteFields(v.Index(idx), fullpath, path[1:], payload)
 	case reflect.Interface:
 		if v.NumMethod() == 0 {

configuration/parser_test.go

@@ -10,19 +10,37 @@ import (
 type localConfiguration struct {
 	Version       Version `yaml:"version"`
 	Log           *Log    `yaml:"log"`
+	Notifications []Notif `yaml:"notifications,omitempty"`
 }
 
 type Log struct {
 	Formatter string `yaml:"formatter,omitempty"`
 }
 
+type Notif struct {
+	Name string `yaml:"name"`
+}
+
 var expectedConfig = localConfiguration{
 	Version: "0.1",
 	Log: &Log{
 		Formatter: "json",
 	},
+	Notifications: []Notif{
+		{Name: "foo"},
+		{Name: "bar"},
+		{Name: "car"},
+	},
 }
 
+const testConfig = `version: "0.1"
+log:
+  formatter: "text"
+notifications:
+  - name: "foo"
+  - name: "bar"
+  - name: "car"`
+
 type ParserSuite struct{}
 
 var _ = check.Suite(new(ParserSuite))
@@ -43,17 +61,32 @@ func (suite *ParserSuite) TestParserOverwriteIninitializedPoiner(c *check.C) {
 		},
 	})
 
-	err := p.Parse([]byte(`{version: "0.1", log: {formatter: "text"}}`), &config)
+	err := p.Parse([]byte(testConfig), &config)
 	c.Assert(err, check.IsNil)
 	c.Assert(config, check.DeepEquals, expectedConfig)
 }
 
+const testConfig2 = `version: "0.1"
+log:
+  formatter: "text"
+notifications:
+  - name: "val1"
+  - name: "val2"
+  - name: "car"`
+
 func (suite *ParserSuite) TestParseOverwriteUnininitializedPoiner(c *check.C) {
 	config := localConfiguration{}
 
 	os.Setenv("REGISTRY_LOG_FORMATTER", "json")
 	defer os.Unsetenv("REGISTRY_LOG_FORMATTER")
 
+	// override only first two notificationsvalues
+	// in the tetConfig: leave the last value unchanged.
+	os.Setenv("REGISTRY_NOTIFICATIONS_0_NAME", "foo")
+	defer os.Unsetenv("REGISTRY_NOTIFICATIONS_0_NAME")
+	os.Setenv("REGISTRY_NOTIFICATIONS_1_NAME", "bar")
+	defer os.Unsetenv("REGISTRY_NOTIFICATIONS_1_NAME")
+
 	p := NewParser("registry", []VersionedParseInfo{
 		{
 			Version: "0.1",
@@ -64,7 +97,7 @@ func (suite *ParserSuite) TestParseOverwriteUnininitializedPoiner(c *check.C) {
 		},
 	})
 
-	err := p.Parse([]byte(`{version: "0.1"}`), &config)
+	err := p.Parse([]byte(testConfig2), &config)
 	c.Assert(err, check.IsNil)
 	c.Assert(config, check.DeepEquals, expectedConfig)
 }