error: fix flagname for shorthandonly

Author: rsteube

.github/workflows/go.yml

@@ -22,7 +22,7 @@ jobs:
     - name: Set up Go
       uses: actions/setup-go@v2
       with:
-        go-version: 1.19
+        go-version: '1.25.1'
 
     - name: Build
       run: go build -v ./...

errors.go

@@ -14,6 +14,7 @@ const (
 	flagNoSuchFlagMessage
 	flagUnknownFlagMessage
 	flagUnknownShorthandFlagMessage
+	flagUnknownShorthandFlagMessageNonPosix
 )
 
 // NotExistError is the error returned when trying to access a flag that
@@ -42,6 +43,9 @@ func (e *NotExistError) Error() string {
 	case flagUnknownShorthandFlagMessage:
 		c := rune(e.name[0])
 		return fmt.Sprintf("unknown shorthand flag: %q in -%s", c, e.specifiedShorthands)
+
+	case flagUnknownShorthandFlagMessageNonPosix:
+		return fmt.Sprintf("unknown shorthand flag: -%s", e.name)
 	}
 
 	panic(fmt.Errorf("unknown flagNotExistErrorMessageType: %v", e.messageType))
@@ -109,7 +113,14 @@ func (e *InvalidValueError) Error() string {
 	flag := e.flag
 	var flagName string
 	if flag.Shorthand != "" && flag.ShorthandDeprecated == "" {
-		flagName = fmt.Sprintf("-%s, --%s", flag.Shorthand, flag.Name)
+		flagName = fmt.Sprintf("-%s", flag.Shorthand)
+		if flag.Mode != ShorthandOnly {
+			if flag.Mode != NameAsShorthand {
+				flagName = fmt.Sprintf("%s, --%s", flagName, flag.Name)
+			} else {
+				flagName = fmt.Sprintf("%s, -%s", flagName, flag.Name)
+			}
+		}
 	} else {
 		flagName = fmt.Sprintf("--%s", flag.Name)
 	}

flag.go

@@ -1200,9 +1200,8 @@ func (f *FlagSet) parseSingleShortArg(shorthands string, args []string, fn parse
 			} else {
 				// custom carapace-sh/carapace-pflag message for non-posix shorthand (chain disabled)
 				err = f.fail(&NotExistError{
-					name: name,
-					// specifiedShorthands: shorthands,
-					messageType: flagUnknownShorthandFlagMessage,
+					name:        name,
+					messageType: flagUnknownShorthandFlagMessageNonPosix,
 				})
 			}
 			return