From a0df5f33915247a80a077ec48ed14a8ad5579da4 Mon Sep 17 00:00:00 2001
From: Alex Flint <alex.flint@gmail.com>
Date: Sat, 13 Jan 2018 14:20:00 -0800
Subject: [PATCH] handle negative values

---
 parse.go      | 18 +++++++++++++++++-
 parse_test.go | 22 ++++++++++++++++++++++
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/parse.go b/parse.go
index 462aab9..10c6841 100644
--- a/parse.go
+++ b/parse.go
@@ -345,7 +345,10 @@ func process(specs []*spec, args []string) error {
 
 		// if we have something like "--foo" then the value is the next argument
 		if value == "" {
-			if i+1 == len(args) || isFlag(args[i+1]) {
+			if i+1 == len(args) {
+				return fmt.Errorf("missing value for %s", arg)
+			}
+			if !nextIsNumeric(spec.dest.Type(), args[i+1]) && isFlag(args[i+1]) {
 				return fmt.Errorf("missing value for %s", arg)
 			}
 			value = args[i+1]
@@ -387,6 +390,19 @@ func process(specs []*spec, args []string) error {
 	return nil
 }
 
+func nextIsNumeric(t reflect.Type, s string) bool {
+	switch t.Kind() {
+	case reflect.Ptr:
+		return nextIsNumeric(t.Elem(), s)
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Float32, reflect.Float64, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		v := reflect.New(t)
+		err := scalar.ParseValue(v, s)
+		return err == nil
+	default:
+		return false
+	}
+}
+
 // isFlag returns true if a token is a flag such as "-v" or "--user" but not "-" or "--"
 func isFlag(s string) bool {
 	return strings.HasPrefix(s, "-") && strings.TrimLeft(s, "-") != ""
diff --git a/parse_test.go b/parse_test.go
index 701b105..925a23e 100644
--- a/parse_test.go
+++ b/parse_test.go
@@ -67,6 +67,28 @@ func TestInt(t *testing.T) {
 	assert.EqualValues(t, 8, *args.Ptr)
 }
 
+func TestNegativeInt(t *testing.T) {
+	var args struct {
+		Foo int
+	}
+	err := parse("-foo -100", &args)
+	require.NoError(t, err)
+	assert.EqualValues(t, args.Foo, -100)
+}
+
+func TestNegativeIntAndFloatAndTricks(t *testing.T) {
+	var args struct {
+		Foo int
+		Bar float64
+		N   int `arg:"--100"`
+	}
+	err := parse("-foo -100 -bar -60.14 -100 -100", &args)
+	require.NoError(t, err)
+	assert.EqualValues(t, args.Foo, -100)
+	assert.EqualValues(t, args.Bar, -60.14)
+	assert.EqualValues(t, args.N, -100)
+}
+
 func TestUint(t *testing.T) {
 	var args struct {
 		Foo uint