add CopyToGoFlagSet

This is useful for programs which want to define some flags with pflag (for
example, in external packages) but still need to use Go flag command line
parsing to preserve backward compatibility with previous releases, in
particular support for single-dash flags.

Without this in pflag, such tools have to resort to copying via the public
API, which leads to less useful help messages (type of basic values
will be unknown).

1 files changed, 34 insertions, 0 deletions

diff --git a/golangflag.go b/golangflag.go
index f563907..e62eab5 100644
--- a/golangflag.go
+++ b/golangflag.go
@@ -8,6 +8,7 @@ import (
 	goflag "flag"
 	"reflect"
 	"strings"
+	"time"
 )
 
 // go test flags prefixes
@@ -113,6 +114,38 @@ func (f *FlagSet) AddGoFlagSet(newSet *goflag.FlagSet) {
 	f.addedGoFlagSets = append(f.addedGoFlagSets, newSet)
 }
 
+// CopyToGoFlagSet will add all current flags to the given Go flag set.
+// Deprecation remarks get copied into the usage description.
+// Whenever possible, a flag gets added for which Go flags shows
+// a proper type in the help message.
+func (f *FlagSet) CopyToGoFlagSet(newSet *goflag.FlagSet) {
+	f.VisitAll(func(flag *Flag) {
+		usage := flag.Usage
+		if flag.Deprecated != "" {
+			usage += " (DEPRECATED: " + flag.Deprecated + ")"
+		}
+
+		switch value := flag.Value.(type) {
+		case *stringValue:
+			newSet.StringVar((*string)(value), flag.Name, flag.DefValue, usage)
+		case *intValue:
+			newSet.IntVar((*int)(value), flag.Name, *(*int)(value), usage)
+		case *int64Value:
+			newSet.Int64Var((*int64)(value), flag.Name, *(*int64)(value), usage)
+		case *uintValue:
+			newSet.UintVar((*uint)(value), flag.Name, *(*uint)(value), usage)
+		case *uint64Value:
+			newSet.Uint64Var((*uint64)(value), flag.Name, *(*uint64)(value), usage)
+		case *durationValue:
+			newSet.DurationVar((*time.Duration)(value), flag.Name, *(*time.Duration)(value), usage)
+		case *float64Value:
+			newSet.Float64Var((*float64)(value), flag.Name, *(*float64)(value), usage)
+		default:
+			newSet.Var(flag.Value, flag.Name, usage)
+		}
+	})
+}
+
 // ParseSkippedFlags explicitly Parses go test flags (i.e. the one starting with '-test.') with goflag.Parse(),
 // since by default those are skipped by pflag.Parse().
 // Typical usage example: `ParseGoTestFlags(os.Args[1:], goflag.CommandLine)`
@@ -125,3 +158,4 @@ func ParseSkippedFlags(osArgs []string, goFlagSet *goflag.FlagSet) error {
 	}
 	return goFlagSet.Parse(skippedFlags)
 }
+