mstr: parameterize Trunc on string or []byte

mstr/mstr.go

@@ -10,7 +10,7 @@ import (
 // exceeds this length, it is truncated at a point ≤ n so that the result does
 // not end in a partial UTF-8 encoding. Trunc does not verify that s is valid
 // UTF-8, but if it is the result will remain valid after truncation.
-func Trunc(s string, n int) string {
+func Trunc[String ~string | ~[]byte](s String, n int) String {
 	if n >= len(s) {
 		return s
 	}

mstr/mstr_test.go

@@ -28,7 +28,10 @@ func TestTrunc(t *testing.T) {
 	for _, tc := range tests {
 		got := mstr.Trunc(tc.input, tc.size)
 		if got != tc.want {
-			t.Errorf("Trunc(%q, %d): got %q, want %q", tc.input, tc.size, got, tc.want)
+			t.Errorf("Trunc(%q, %d) [string]: got %q, want %q", tc.input, tc.size, got, tc.want)
+		}
+		if got := mstr.Trunc([]byte(tc.input), tc.size); string(got) != tc.want {
+			t.Errorf("Trunc(%q, %d) [bytes]: got %q, want %q", tc.input, tc.size, got, tc.want)
 		}
 	}
 }