Refactor to support proper types; add tests

altsrc/default_input_source.go

@@ -1,6 +1,8 @@
 package altsrc
 
-// defaultInputSource creates a default InputSourceContext.
-func defaultInputSource() (InputSourceContext, error) {
+import "github.com/urfave/cli/v2"
+
+// defaultInputSource creates a default cli.InputSourceContext.
+func defaultInputSource() (cli.InputSourceContext, error) {
 	return &MapInputSource{file: "", valueMap: map[interface{}]interface{}{}}, nil
 }

altsrc/detect_input_source.go

@@ -3,22 +3,23 @@ package altsrc
 import (
 	"fmt"
 	"path/filepath"
+	"sort"
 
 	"github.com/urfave/cli/v2"
 )
 
 // defaultSources is a read-only map, making it concurrency-safe
-var defaultSources = map[string]func(string) func(*cli.Context) (InputSourceContext, error){
+var defaultSources = map[string]func(string) func(*cli.Context) (cli.InputSourceContext, error){
 	".conf": NewTomlSourceFromFlagFunc,
 	".json": NewJSONSourceFromFlagFunc,
 	".toml": NewTomlSourceFromFlagFunc,
 	".yaml": NewYamlSourceFromFlagFunc,
 	".yml":  NewYamlSourceFromFlagFunc,
 }
 
-// DetectNewSourceFromFlagFunc creates a new InputSourceContext from a provided flag name and source context.
-func DetectNewSourceFromFlagFunc(flagFileName string) func(*cli.Context) (InputSourceContext, error) {
-	return func(cCtx *cli.Context) (InputSourceContext, error) {
+// DetectNewSourceFromFlagFunc creates a new cli.InputSourceContext from a provided flag name and source context.
+func DetectNewSourceFromFlagFunc(flagFileName string) func(*cli.Context) (cli.InputSourceContext, error) {
+	return func(cCtx *cli.Context) (cli.InputSourceContext, error) {
 		detectableSources := cCtx.App.GetDetectableSources()
 
 		if fileFullPath := cCtx.String(flagFileName); fileFullPath != "" {
@@ -28,17 +29,7 @@ func DetectNewSourceFromFlagFunc(flagFileName string) func(*cli.Context) (InputS
 
 			// Check if the App contains a handler for this extension first, allowing it to override the defaults
 			if handler, ok := detectableSources[fileExt]; ok {
-				source, err := handler(flagFileName)(cCtx)
-				if err != nil {
-					return nil, err
-				}
-
-				switch source := source.(type) {
-				case InputSourceContext:
-					return source, nil
-				default:
-					typeError = fmt.Errorf("Unable to parse config file. The type handler for %s is incorrectly implemented.", fileExt)
-				}
+				return handler(flagFileName)(cCtx)
 			}
 
 			// Fall back to the default sources implemented by the library itself
@@ -57,17 +48,10 @@ func DetectNewSourceFromFlagFunc(flagFileName string) func(*cli.Context) (InputS
 	}
 }
 
-func detectableExtensions(detectableSources map[string]func(string) func(*cli.Context) (interface{}, error)) []string {
-	detectLen := len(detectableSources)
-	defaultLen := len(defaultSources)
-
-	largerLen := defaultLen
-	if detectLen > defaultLen {
-		largerLen = detectLen
-	}
-
-	// The App might override some file extensions, so set size to fit the larger of the two lists, with capacity for both in case it's needed
-	extensions := make([]string, largerLen, detectLen+defaultLen)
+func detectableExtensions(detectableSources map[string]func(string) func(*cli.Context) (cli.InputSourceContext, error)) []string {
+	// We don't preallocate because this generates empty space in the output
+	// It's less efficient, but this is for error messaging only at the moment
+	var extensions []string
 
 	for ext := range detectableSources {
 		extensions = append(extensions, ext)
@@ -79,5 +63,7 @@ func detectableExtensions(detectableSources map[string]func(string) func(*cli.Co
 		}
 	}
 
+	sort.Strings(extensions)
+
 	return extensions
 }