Single configuration file extensions

The application configuration file loader supported multiple file types
with multiple file extensions, e.g. `yml` and `yaml` for YAML encoded
data. This could lead to priority problems when merging multiple loaded
configuration states when there are multiple YAML files with different
supported file extension in the same directory. There were no rules how
to decide which extension takes precedence over another extension
causing unexpected merged configurations.

To prevent such problems each file type now only supports a single
official file extension. The currently supported encodings are JSON (1)
and YAML (2) where the following file extension are only supported:

1. JSON
  - before: `*.json`
  - after: `*.json`
2. YAML
  - before: `*.yml, *.yaml`
  - after: `*.yml`

Note that this won't affect the precedences of different file types!
YAML files still take precedence over JSON files since YAML is a
superset of JSON and JSON is also valid YAML.

References:
  (1) https://www.json.org
  (2) https://yaml.org

Epic GH-33
Resolves GH-67

pkg/config/constants.go

@@ -53,28 +53,16 @@ func init() {
 func genConfigPaths() []*file.File {
 	var files []*file.File
 
-	// Include user-level dot-file configurations from the user's home directory.
+	// Include the user-level dotfile configuration from user's home directory.
 	home, err := homedir.Dir()
 	if err == nil {
-		for _, ext := range encoder.ExtensionsJson {
-			files = append(files, file.NewFile(filepath.Join(home, fmt.Sprintf(".%s.%s", ProjectName, ext))))
-		}
-		// Since YAML is a superset of JSON, YAML files take precedence over pure JSON based configurations.
-		for _, ext := range encoder.ExtensionsYaml {
-			files = append(files, file.NewFile(filepath.Join(home, fmt.Sprintf(".%s.%s", ProjectName, ext))))
-		}
+		files = append(files, file.NewFile(filepath.Join(home, fmt.Sprintf(".%s.%s", ProjectName, encoder.ExtensionsYaml))))
 	}
 
-	// Files placed in the current working directory take precedence over user-level configurations.
+	// A file placed in the current working directory takes precedence over the user-level configuration.
 	pwd, err := os.Getwd()
 	if err == nil {
-		for _, ext := range encoder.ExtensionsJson {
-			files = append(files, file.NewFile(filepath.Join(pwd, fmt.Sprintf("%s.%s", ProjectName, ext))))
-		}
-		// Since YAML is a superset of JSON, YAML files take precedence over pure JSON based configurations.
-		for _, ext := range encoder.ExtensionsYaml {
-			files = append(files, file.NewFile(filepath.Join(pwd, fmt.Sprintf("%s.%s", ProjectName, ext))))
-		}
+		files = append(files, file.NewFile(filepath.Join(pwd, fmt.Sprintf("%s.%s", ProjectName, encoder.ExtensionsYaml))))
 	}
 
 	return files

pkg/config/encoder/constants.go

@@ -19,12 +19,11 @@ import (
 var (
 	// ExtensionMapping maps supported file extensions to their compatible encoders.
 	ExtensionMapping = map[string]Encoder{
-		"json": json.NewJsonEncoder(),
-		"yaml": yaml.NewYamlEncoder(),
-		"yml":  yaml.NewYamlEncoder(),
+		ExtensionsJson: json.NewJsonEncoder(),
+		ExtensionsYaml: yaml.NewYamlEncoder(),
 	}
-	// ExtensionsJson stores all supported extensions for files containing JSON data.
-	ExtensionsJson = []string{"json"}
-	// ExtensionsYaml stores all supported extensions for files containing YAML data.
-	ExtensionsYaml = []string{"yaml", "yml"}
+	// ExtensionsJson is the supported extension for files containing JSON data.
+	ExtensionsJson = "json"
+	// ExtensionsYaml is the supported extension for files containing YAML data.
+	ExtensionsYaml = "yml"
 )