From 5386ade0f7a88a6fcbaa384d99e61563deac76ae Mon Sep 17 00:00:00 2001
From: Sergey Kamardin <gobwas@gmail.com>
Date: Fri, 16 Oct 2020 23:39:12 +0300
Subject: [PATCH] SetActual() impl

---
 flagutil.go      | 26 ++++++++++++++++++++++++++
 flagutil_test.go | 44 ++++++++++++++++++++++++++++++++++++++++----
 2 files changed, 66 insertions(+), 4 deletions(-)

diff --git a/flagutil.go b/flagutil.go
index 26e1b24..01e4150 100644
--- a/flagutil.go
+++ b/flagutil.go
@@ -517,6 +517,32 @@ func CombineFlags(f0, f1 *flag.Flag) *flag.Flag {
 	return &r
 }
 
+// SetActual makes flag look like it has been set within flag set.
+// If flag set doesn't has flag with given SetActual() does nothing.
+// Original value of found flag remains untouched, so it is safe to use with
+// flags that accumulate values of multiple Set() calls.
+func SetActual(fs *flag.FlagSet, name string) {
+	f := fs.Lookup(name)
+	if f == nil {
+		return
+	}
+	orig := f.Value
+	defer func() {
+		f.Value = orig
+	}()
+	var didSet bool
+	f.Value = value{
+		doSet: func(s string) error {
+			didSet = s == "dummy"
+			return nil
+		},
+	}
+	fs.Set(name, "dummy")
+	if !didSet {
+		panic("flagutil: make specified didn't work well")
+	}
+}
+
 func mergeUsage(name, s0, s1 string) string {
 	switch {
 	case s0 == "":
diff --git a/flagutil_test.go b/flagutil_test.go
index 4fa6b3b..18082d4 100644
--- a/flagutil_test.go
+++ b/flagutil_test.go
@@ -15,6 +15,21 @@ import (
 	"github.com/gobwas/flagutil/parse"
 )
 
+func TestSetActual(t *testing.T) {
+	fs := flag.NewFlagSet(t.Name(), flag.PanicOnError)
+	fs.String("flag", "default", "usage")
+
+	f := fs.Lookup("flag")
+	f.Value = OverrideSet(f.Value, func(string) error {
+		t.Fatalf("unexpected value change")
+		return nil
+	})
+
+	mustNotBeActual(t, fs, "flag")
+	SetActual(fs, "flag")
+	mustBeActual(t, fs, "flag")
+}
+
 type fullParser struct {
 	Parser
 	Printer
@@ -160,7 +175,7 @@ func ExampleMerge() {
 	)
 	// Now we need to setup same flag (probably from some different place).
 	// Setting it up again in a superset will cause error.
-	Merge(fs, func(sub *flag.FlagSet) {
+	MergeInto(fs, func(sub *flag.FlagSet) {
 		// Notice that default value of this flag is different.
 		// However, it will be discarded in favour of default value from superset.
 		sub.StringVar(&s1,
@@ -197,7 +212,7 @@ func ExampleMerge_different_types() {
 		"foo", "42",
 		"some flag usage here",
 	)
-	Merge(fs, func(sub *flag.FlagSet) {
+	MergeInto(fs, func(sub *flag.FlagSet) {
 		sub.IntVar(&i,
 			"foo", 84,
 			"another flag usage here",
@@ -222,10 +237,10 @@ func TestMerge(t *testing.T) {
 		"foo", "bar",
 		"superset usage",
 	)
-	Merge(fs, func(fs *flag.FlagSet) {
+	MergeInto(fs, func(fs *flag.FlagSet) {
 		fs.StringVar(&s1, "foo", "baz", "subset1 usage")
 	})
-	Merge(fs, func(fs *flag.FlagSet) {
+	MergeInto(fs, func(fs *flag.FlagSet) {
 		fs.StringVar(&s2, "foo", "baq", "subset2 usage")
 	})
 	if s0 == s1 || s1 == s2 {
@@ -323,6 +338,27 @@ func mustBeDefined(t *testing.T, fs *flag.FlagSet, name string) {
 	}
 }
 
+func mustBeActual(t *testing.T, fs *flag.FlagSet, name string) {
+	if !isActual(fs, name) {
+		t.Fatalf("want flag %q to be actual in set", name)
+	}
+}
+
+func mustNotBeActual(t *testing.T, fs *flag.FlagSet, name string) {
+	if isActual(fs, name) {
+		t.Fatalf("want flag %q to not be actual in set", name)
+	}
+}
+
+func isActual(fs *flag.FlagSet, name string) (actual bool) {
+	fs.Visit(func(f *flag.Flag) {
+		if f.Name == name {
+			actual = true
+		}
+	})
+	return
+}
+
 func TestCombineFlags(t *testing.T) {
 	for _, test := range []struct {
 		name  string