feat: improve flag error handling

config.go

@@ -5,8 +5,8 @@ import (
 	"fmt"
 	"os"
 	"path/filepath"
-	"strings"
 	"text/template"
+	"time"
 
 	"github.com/adrg/xdg"
 	"github.com/caarlos0/env/v9"
@@ -127,36 +127,6 @@ type Config struct {
 	cacheReadFromID, cacheWriteToID, cacheWriteToTitle string
 }
 
-type flagParseError struct {
-	err error
-}
-
-func (f flagParseError) Error() string {
-	return fmt.Sprintf("missing flag: %s", f.Flag())
-}
-
-func (f flagParseError) ReasonFormat() string {
-	s := f.err.Error()
-	switch {
-	case strings.Contains(s, "flag needs an argument"):
-		return "Flag %s needs an argument."
-	default:
-		return "Flag %s is missing."
-	}
-}
-
-func (f flagParseError) Flag() string {
-	ps := strings.Split(f.err.Error(), "-")
-	switch len(ps) {
-	case 2: //nolint:gomnd
-		return "-" + ps[len(ps)-1]
-	case 3: //nolint:gomnd
-		return "--" + ps[len(ps)-1]
-	default:
-		return ""
-	}
-}
-
 func ensureConfig() (Config, error) {
 	var c Config
 	sp, err := xdg.ConfigFile(filepath.Join("mods", "mods.yml"))

flag.go

@@ -0,0 +1,65 @@
+package main
+
+import (
+	"regexp"
+	"strings"
+	"time"
+
+	"github.com/caarlos0/duration"
+)
+
+func newFlagParseError(err error) flagParseError {
+	var reason, flag string
+	s := err.Error()
+	switch {
+	case strings.HasPrefix(s, "flag needs an argument:"):
+		reason = "Flag %s needs an argument."
+		ps := strings.Split(s, "-")
+		switch len(ps) {
+		case 2: //nolint:gomnd
+			flag = "-" + ps[len(ps)-1]
+		case 3: //nolint:gomnd
+			flag = "--" + ps[len(ps)-1]
+		}
+	case strings.HasPrefix(s, "unknown flag:"):
+		reason = "Flag %s is missing."
+		flag = strings.TrimPrefix(s, "unknown flag: ")
+	case strings.HasPrefix(s, "invalid argument"):
+		reason = "Flag %s have an invalid argument."
+		re := regexp.MustCompile(`invalid argument ".*" for "(.*)" flag: .*`)
+		parts := re.FindStringSubmatch(s)
+		if len(parts) > 1 {
+			flag = parts[1]
+		}
+	default:
+		reason = s
+	}
+	return flagParseError{
+		err:    err,
+		reason: reason,
+		flag:   flag,
+	}
+}
+
+type flagParseError struct {
+	err    error
+	reason string
+	flag   string
+}
+
+func (f flagParseError) Error() string {
+	return f.err.Error()
+}
+
+func (f flagParseError) ReasonFormat() string {
+	return f.reason
+}
+
+func (f flagParseError) Flag() string {
+	return f.flag
+}
+
+func newDurationFlag(val time.Duration, p *time.Duration) *durationFlag {
+	*p = val
+	return (*durationFlag)(p)
+}

flag_test.go

@@ -0,0 +1,56 @@
+package main
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+var flagParseErrorTests = []struct {
+	in     string
+	flag   string
+	reason string
+}{
+	{
+		"unknown flag: --nope",
+		"--nope",
+		"Flag %s is missing.",
+	},
+	{
+		"flag needs an argument: --delete",
+		"--delete",
+		"Flag %s needs an argument.",
+	},
+	{
+		"flag needs an argument: 'd' in -d",
+		"-d",
+		"Flag %s needs an argument.",
+	},
+	{
+		`invalid argument "20dd" for "--delete-older-than" flag: time: unknown unit "dd" in duration "20dd"`,
+		"--delete-older-than",
+		"Flag %s have an invalid argument.",
+	},
+	{
+		`invalid argument "sdfjasdl" for "--max-tokens" flag: strconv.ParseInt: parsing "sdfjasdl": invalid syntax`,
+		"--max-tokens",
+		"Flag %s have an invalid argument.",
+	},
+	{
+		`invalid argument "nope" for "-r, --raw" flag: strconv.ParseBool: parsing "nope": invalid syntax`,
+		"-r, --raw",
+		"Flag %s have an invalid argument.",
+	},
+}
+
+func TestFlagParseError(t *testing.T) {
+	for _, tf := range flagParseErrorTests {
+		t.Run(tf.in, func(t *testing.T) {
+			err := newFlagParseError(fmt.Errorf(tf.in))
+			require.Equal(t, tf.flag, err.Flag())
+			require.Equal(t, tf.reason, err.ReasonFormat())
+			require.Equal(t, tf.in, err.Error())
+		})
+	}
+}

main.go

@@ -54,7 +54,7 @@ func init() {
 	buildVersion()
 	rootCmd.SetUsageFunc(usageFunc)
 	rootCmd.SetFlagErrorFunc(func(_ *cobra.Command, err error) error {
-		return flagParseError{err: err}
+		return newFlagParseError(err)
 	})
 
 	rootCmd.CompletionOptions.HiddenDefaultCmd = true