From 268215359e7eec34a8c0d34476472240c8a9284f Mon Sep 17 00:00:00 2001
From: Samuel Berthe <dev@samuel-berthe.fr>
Date: Thu, 25 Sep 2025 04:21:56 +0200
Subject: [PATCH] fix(string): fix division by zero (#684)

---
 string.go      | 11 +++++++++++
 string_test.go |  4 ++++
 2 files changed, 15 insertions(+)

diff --git a/string.go b/string.go
index f4aa85c..19a3c45 100644
--- a/string.go
+++ b/string.go
@@ -43,6 +43,17 @@ func RandomString(size int, charset []rune) string {
 	// see https://stackoverflow.com/questions/22892120/how-to-generate-a-random-string-of-a-fixed-length-in-go
 	sb := strings.Builder{}
 	sb.Grow(size)
+
+	if len(charset) == 1 {
+		// Edge case, because if the charset is a single character,
+		// it will panic below (divide by zero).
+		// -> https://github.com/samber/lo/issues/679
+		for i := 0; i < size; i++ {
+			sb.WriteRune(charset[0])
+		}
+		return sb.String()
+	}
+
 	// Calculate the number of bits required to represent the charset,
 	// e.g., for 62 characters, it would need 6 bits (since 62 -> 64 = 2^6)
 	letterIDBits := int(math.Log2(float64(nearestPowerOfTwo(len(charset)))))
diff --git a/string_test.go b/string_test.go
index ba7f7a2..30aeca2 100644
--- a/string_test.go
+++ b/string_test.go
@@ -29,6 +29,10 @@ func TestRandomString(t *testing.T) {
 
 	is.PanicsWithValue("lo.RandomString: charset must not be empty", func() { RandomString(100, []rune{}) })
 	is.PanicsWithValue("lo.RandomString: size must be greater than 0", func() { RandomString(0, LowerCaseLettersCharset) })
+
+	str4 := RandomString(10, []rune{65})
+	is.Equal(10, RuneLength(str4))
+	is.Subset([]rune{65, 65, 65, 65, 65, 65, 65, 65, 65, 65}, []rune(str4))
 }
 
 func TestChunkString(t *testing.T) {