From 302f5d9d515c1796a93ebe64c6c8eda39106ed43 Mon Sep 17 00:00:00 2001
From: dualfroz <me@dualfroz.com>
Date: Fri, 4 Sep 2026 09:31:42 +0200
Subject: [PATCH] fix(flag): honor full separator length when splitting map
 key=value pairs

splitKeyVal sliced the value from index+1, skipping only one byte of the
key/value separator. With a multi-character sep tag (e.g. sep:"=>") the
remaining separator bytes leaked into the value. Slice from index+len(sep)
so the whole separator is consumed.
---
 cli_test.go | 21 +++++++++++++++++++++
 flag.go     |  2 +-
 2 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/cli_test.go b/cli_test.go
index ab79c43..068208b 100644
--- a/cli_test.go
+++ b/cli_test.go
@@ -727,3 +727,24 @@ func TestDecoder(t *testing.T) {
 	assert.Nil(t, flagSet.err)
 	assert.Equal(t, v.D, customT{K1: "string", K2: 2})
 }
+
+func TestMapMultiCharSep(t *testing.T) {
+	// A multi-character separator must not leak its tail into the value.
+	if k, v, _ := splitKeyVal("key=>val", "=>"); k != "key" || v != "val" {
+		t.Errorf(`splitKeyVal("key=>val", "=>") = (%q, %q), want ("key", "val")`, k, v)
+	}
+
+	// Public API: a map flag configured with a multi-char sep.
+	type T struct {
+		Map map[string]string `cli:"m" sep:"=>"`
+	}
+	clr := color.Color{}
+	v := new(T)
+	flagSet := parseArgv([]string{"-mkey=>val"}, v, clr)
+	if flagSet.err != nil {
+		t.Fatalf("unexpected error: %v", flagSet.err)
+	}
+	if got := v.Map["key"]; got != "val" {
+		t.Errorf(`map value = %q, want "val"`, got)
+	}
+}
diff --git a/flag.go b/flag.go
index 55b71cf..b57c0e4 100644
--- a/flag.go
+++ b/flag.go
@@ -436,7 +436,7 @@ func splitKeyVal(s, sep string) (key, val string, err error) {
 	if index == -1 {
 		return s, "", nil
 	}
-	return s[:index], s[index+1:], nil
+	return s[:index], s[index+len(sep):], nil
 }
 
 func minmaxIntCheck(kind reflect.Kind, v int64) bool {