From 07e4d07d17fcf91ba5b0a2637f9b4f179d960c7c Mon Sep 17 00:00:00 2001
From: Tomas Aschan <1550920+tomasaschan@users.noreply.github.com>
Date: Thu, 17 Jul 2025 11:54:51 +0200
Subject: [PATCH] Make Value a drop-in replacement for flag.Value

---
 flag.go | 28 +++++++++++++++++++++++-----
 text.go |  4 ++--
 time.go |  4 ++--
 3 files changed, 27 insertions(+), 9 deletions(-)

diff --git a/flag.go b/flag.go
index 107fa190..b4b57cfa 100644
--- a/flag.go
+++ b/flag.go
@@ -200,6 +200,15 @@ type Flag struct {
 type Value interface {
 	String() string
 	Set(string) error
+}
+
+// TypedValue wraps Value but adds an additional Type() string, which
+// can be used to special-case things like usage instructions, error
+// messages, parsing, etc.
+// Its value should be a constant string that identifies the type of
+// the underlying flag value.
+type TypedValue interface {
+	Value
 	Type() string
 }
 
@@ -398,8 +407,8 @@ func (f *FlagSet) getFlagType(name string, ftype string, convFunc func(sval stri
 		return nil, err
 	}
 
-	if flag.Value.Type() != ftype {
-		err := fmt.Errorf("trying to get %s value of flag of type %s", ftype, flag.Value.Type())
+	if tvalue, ok := flag.Value.(TypedValue); ok && tvalue.Type() != ftype {
+		err := fmt.Errorf("trying to get %s value of flag of type %s", ftype, tvalue.Type())
 		return nil, err
 	}
 
@@ -597,7 +606,10 @@ func UnquoteUsage(flag *Flag) (name string, usage string) {
 		}
 	}
 
-	name = flag.Value.Type()
+	name = "value"
+	if tvalue, ok := flag.Value.(TypedValue); ok {
+		name = tvalue.Type()
+	}
 	switch name {
 	case "bool", "boolfunc":
 		name = ""
@@ -716,8 +728,14 @@ func (f *FlagSet) FlagUsagesWrapped(cols int) string {
 		if varname != "" {
 			line += " " + varname
 		}
+		tvalue, tvalueOk := flag.Value.(TypedValue)
 		if flag.NoOptDefVal != "" {
-			switch flag.Value.Type() {
+			if !tvalueOk {
+				line += fmt.Sprintf(" [=%s]", flag.NoOptDefVal)
+				return
+			}
+
+			switch tvalue.Type() {
 			case "string":
 				line += fmt.Sprintf("[=\"%s\"]", flag.NoOptDefVal)
 			case "bool", "boolfunc":
@@ -742,7 +760,7 @@ func (f *FlagSet) FlagUsagesWrapped(cols int) string {
 
 		line += usage
 		if !flag.defaultIsZeroValue() {
-			if flag.Value.Type() == "string" {
+			if tvalueOk && tvalue.Type() == "string" {
 				line += fmt.Sprintf(" (default %q)", flag.DefValue)
 			} else {
 				line += fmt.Sprintf(" (default %s)", flag.DefValue)
diff --git a/text.go b/text.go
index 886d5a3d..8319d0b2 100644
--- a/text.go
+++ b/text.go
@@ -54,8 +54,8 @@ func (f *FlagSet) GetText(name string, out encoding.TextUnmarshaler) error {
 	if flag == nil {
 		return fmt.Errorf("flag accessed but not defined: %s", name)
 	}
-	if flag.Value.Type() != reflect.TypeOf(out).Name() {
-		return fmt.Errorf("trying to get %s value of flag of type %s", reflect.TypeOf(out).Name(), flag.Value.Type())
+	if tvalue, ok := flag.Value.(TypedValue); ok && tvalue.Type() != reflect.TypeOf(out).Name() {
+		return fmt.Errorf("trying to get %s value of flag of type %s", reflect.TypeOf(out).Name(), tvalue.Type())
 	}
 	return out.UnmarshalText([]byte(flag.Value.String()))
 }
diff --git a/time.go b/time.go
index dc024807..d0d44d80 100644
--- a/time.go
+++ b/time.go
@@ -58,8 +58,8 @@ func (f *FlagSet) GetTime(name string) (time.Time, error) {
 		return time.Time{}, err
 	}
 
-	if flag.Value.Type() != "time" {
-		err := fmt.Errorf("trying to get %s value of flag of type %s", "time", flag.Value.Type())
+	if tvalue, ok := flag.Value.(TypedValue); ok && tvalue.Type() != "time" {
+		err := fmt.Errorf("trying to get %s value of flag of type %s", "time", tvalue.Type())
 		return time.Time{}, err
 	}