Switch to an extensions model

- Move things back to `altsrc`
- Add support for extensions to `App`
- Implement `DetectableSourcesAppExtension` to hold `detectableSources`
- Refactor code and tests for the revised setup, including making the
  extension only needed for adding additional handlers

altsrc/default_input_source.go

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

altsrc/detect_input_source.go

@@ -9,25 +9,29 @@ import (
 )
 
 // defaultSources is a read-only map, making it concurrency-safe
-var defaultSources = map[string]func(string) func(*cli.Context) (cli.InputSourceContext, error){
+var defaultSources = map[string]func(string) func(*cli.Context) (InputSourceContext, error){
 	".conf": NewTomlSourceFromFlagFunc,
 	".json": NewJSONSourceFromFlagFunc,
 	".toml": NewTomlSourceFromFlagFunc,
 	".yaml": NewYamlSourceFromFlagFunc,
 	".yml":  NewYamlSourceFromFlagFunc,
 }
 
-// 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()
-
+// 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) {
 		if fileFullPath := cCtx.String(flagFileName); fileFullPath != "" {
+			detectableSources := make(map[string]func(string) func(*cli.Context) (InputSourceContext, error))
 			fileExt := filepath.Ext(fileFullPath)
 
 			// Check if the App contains a handler for this extension first, allowing it to override the defaults
-			if handler, ok := detectableSources[fileExt]; ok {
-				return handler(flagFileName)(cCtx)
+			detectExt, isType := cCtx.App.GetExtension("DetectableSources").(DetectableSourcesAppExtension)
+			if isType {
+				detectableSources = detectExt.getDetectableSources()
+
+				if handler, ok := detectableSources[fileExt]; ok {
+					return handler(flagFileName)(cCtx)
+				}
 			}
 
 			// Fall back to the default sources implemented by the library itself
@@ -42,7 +46,7 @@ func DetectNewSourceFromFlagFunc(flagFileName string) func(*cli.Context) (cli.In
 	}
 }
 
-func detectableExtensions(detectableSources map[string]func(string) func(*cli.Context) (cli.InputSourceContext, error)) []string {
+func detectableExtensions(detectableSources map[string]func(string) func(*cli.Context) (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

altsrc/detect_input_source_test.go

@@ -10,7 +10,7 @@ import (
 )
 
 func TestDetectsConfCorrectly(t *testing.T) {
-	app := &cli.App{}
+	app := cli.NewApp()
 	set := flag.NewFlagSet("test", 0)
 	_ = os.WriteFile("current.conf", []byte("test = 15"), 0666)
 	defer os.Remove("current.conf")
@@ -40,7 +40,7 @@ func TestDetectsConfCorrectly(t *testing.T) {
 }
 
 func TestDetectsJsonCorrectly(t *testing.T) {
-	app := &cli.App{}
+	app := cli.NewApp()
 	set := flag.NewFlagSet("test", 0)
 	_ = os.WriteFile("current.json", []byte("{\"test\":15}"), 0666)
 	defer os.Remove("current.json")
@@ -70,7 +70,7 @@ func TestDetectsJsonCorrectly(t *testing.T) {
 }
 
 func TestDetectsTomlCorrectly(t *testing.T) {
-	app := &cli.App{}
+	app := cli.NewApp()
 	set := flag.NewFlagSet("test", 0)
 	_ = os.WriteFile("current.toml", []byte("test = 15"), 0666)
 	defer os.Remove("current.toml")
@@ -100,7 +100,7 @@ func TestDetectsTomlCorrectly(t *testing.T) {
 }
 
 func TestDetectsYamlCorrectly(t *testing.T) {
-	app := &cli.App{}
+	app := cli.NewApp()
 	set := flag.NewFlagSet("test", 0)
 	_ = os.WriteFile("current.yaml", []byte("test: 15"), 0666)
 	defer os.Remove("current.yaml")
@@ -130,7 +130,7 @@ func TestDetectsYamlCorrectly(t *testing.T) {
 }
 
 func TestDetectsYmlCorrectly(t *testing.T) {
-	app := &cli.App{}
+	app := cli.NewApp()
 	set := flag.NewFlagSet("test", 0)
 	_ = os.WriteFile("current.yml", []byte("test: 15"), 0666)
 	defer os.Remove("current.yml")
@@ -160,8 +160,9 @@ func TestDetectsYmlCorrectly(t *testing.T) {
 }
 
 func TestHandlesCustomTypeCorrectly(t *testing.T) {
-	app := &cli.App{}
-	app.RegisterDetectableSource(".custom", NewYamlSourceFromFlagFunc)
+	app := cli.NewApp()
+	app.AddExtension(NewDetectableSourcesAppExtension())
+	app.GetExtension("DetectableSources").(DetectableSourcesAppExtension).RegisterDetectableSource(".custom", NewYamlSourceFromFlagFunc)
 	set := flag.NewFlagSet("test", 0)
 	_ = os.WriteFile("current.custom", []byte("test: 15"), 0666)
 	defer os.Remove("current.custom")
@@ -191,8 +192,9 @@ func TestHandlesCustomTypeCorrectly(t *testing.T) {
 }
 
 func TestAllowsOverrides(t *testing.T) {
-	app := &cli.App{}
-	app.RegisterDetectableSource(".conf", NewYamlSourceFromFlagFunc)
+	app := cli.NewApp()
+	app.AddExtension(NewDetectableSourcesAppExtension())
+	app.GetExtension("DetectableSources").(DetectableSourcesAppExtension).RegisterDetectableSource(".conf", NewYamlSourceFromFlagFunc)
 	set := flag.NewFlagSet("test", 0)
 	_ = os.WriteFile("current.conf", []byte("test: 15"), 0666)
 	defer os.Remove("current.conf")
@@ -222,7 +224,7 @@ func TestAllowsOverrides(t *testing.T) {
 }
 
 func TestFailsOnUnrocegnized(t *testing.T) {
-	app := &cli.App{}
+	app := cli.NewApp()
 	set := flag.NewFlagSet("test", 0)
 	_ = os.WriteFile("current.fake", []byte("test: 15"), 0666)
 	defer os.Remove("current.fake")
@@ -252,7 +254,7 @@ func TestFailsOnUnrocegnized(t *testing.T) {
 }
 
 func TestSilentNoOpWithoutFlag(t *testing.T) {
-	app := &cli.App{}
+	app := cli.NewApp()
 	set := flag.NewFlagSet("test", 0)
 	_ = os.WriteFile("current.conf", []byte("test = 15"), 0666)
 	defer os.Remove("current.conf")
@@ -284,7 +286,7 @@ func TestSilentNoOpWithoutFlag(t *testing.T) {
 func TestLoadDefaultConfig(t *testing.T) {
 	t.Skip("Fix parent implementation for default Flag values to get this working")
 
-	app := &cli.App{}
+	app := cli.NewApp()
 	set := flag.NewFlagSet("test", 0)
 	_ = os.WriteFile("current.conf", []byte("test = 15"), 0666)
 	defer os.Remove("current.conf")

altsrc/detectable_sources_app_extension.go

@@ -0,0 +1,32 @@
+package altsrc
+
+import (
+	"github.com/urfave/cli/v2"
+)
+
+type DetectableSourcesAppExtension struct {
+	detectableSources map[string]func(string) func(*cli.Context) (InputSourceContext, error)
+}
+
+func NewDetectableSourcesAppExtension() DetectableSourcesAppExtension {
+	return DetectableSourcesAppExtension{
+		detectableSources: make(map[string]func(string) func(*cli.Context) (InputSourceContext, error)),
+	}
+}
+
+// MyName satisfies the cli.AppExtension interface, providing a name to register the extension under
+func (e DetectableSourcesAppExtension) MyName() string {
+	return "DetectableSources"
+}
+
+// RegisterDetectableSource lets developers add support for their own altsrc filetypes to the autodetection list.
+func (e DetectableSourcesAppExtension) RegisterDetectableSource(extension string, handler func(string) func(*cli.Context) (InputSourceContext, error)) {
+	if e.detectableSources == nil {
+		e.detectableSources = make(map[string]func(string) func(*cli.Context) (InputSourceContext, error))
+	}
+	e.detectableSources[extension] = handler
+}
+
+func (e DetectableSourcesAppExtension) getDetectableSources() map[string]func(string) func(*cli.Context) (InputSourceContext, error) {
+	return e.detectableSources
+}

altsrc/detectable_sources_app_extension_test.go

@@ -0,0 +1,49 @@
+package altsrc
+
+import (
+	"io"
+	"testing"
+
+	"github.com/urfave/cli/v2"
+)
+
+func newTestApp() *cli.App {
+	a := cli.NewApp()
+	a.Writer = io.Discard
+	a.AddExtension(NewDetectableSourcesAppExtension())
+	return a
+}
+
+func TestRegisterDetectableSource(t *testing.T) {
+	app := newTestApp()
+	testHandler := func(s string) func(*cli.Context) (InputSourceContext, error) {
+		return func(ctx *cli.Context) (InputSourceContext, error) {
+			return testInputSource{}, nil
+		}
+	}
+
+	app.GetExtension("DetectableSources").(DetectableSourcesAppExtension).RegisterDetectableSource(".test", testHandler)
+
+	_, ok := app.GetExtension("DetectableSources").(DetectableSourcesAppExtension).detectableSources[".test"]
+	expect(t, ok, true)
+}
+
+func TestGetDetectableSources(t *testing.T) {
+	app := newTestApp()
+	testHandler := func(s string) func(*cli.Context) (InputSourceContext, error) {
+		return func(ctx *cli.Context) (InputSourceContext, error) {
+			return testInputSource{}, nil
+		}
+	}
+
+	_, ok := app.GetExtension("DetectableSources").(DetectableSourcesAppExtension).getDetectableSources()[".test"]
+	expect(t, ok, false)
+
+	app.GetExtension("DetectableSources").(DetectableSourcesAppExtension).RegisterDetectableSource(".test", testHandler)
+
+	_, ok = app.GetExtension("DetectableSources").(DetectableSourcesAppExtension).detectableSources[".test"]
+	expect(t, ok, true)
+
+	_, ok = app.GetExtension("DetectableSources").(DetectableSourcesAppExtension).getDetectableSources()[".test"]
+	expect(t, ok, true)
+}