cut: don't rewrite a -d= file operand after --

src/uu/cut/src/cut.rs

@@ -1047,8 +1047,15 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     // GNU `cut` supports `-d=` to set the delimiter to `=`.
     // Clap parsing is limited in this situation, see:
     // https://github.com/uutils/coreutils/issues/2424#issuecomment-863825242
+    // Arguments after `--` are file operands and must be left untouched.
+    let mut seen_double_dash = false;
     let args = args.into_iter().map(|x| {
-        if x == "-d=" {
+        if seen_double_dash {
+            x
+        } else if x == "--" {
+            seen_double_dash = true;
+            x
+        } else if x == "-d=" {
             "--delimiter==".into()
         } else {
             x

tests/by-util/test_cut.rs

@@ -367,6 +367,18 @@ fn test_equal_as_delimiter() {
     }
 }
 
+#[test]
+fn test_equal_delimiter_file_operand_after_double_dash() {
+    // After `--`, a file named `-d=` is an operand and must not be rewritten
+    // to `--delimiter==`. #15806
+    let (at, mut ucmd) = at_and_ucmd!();
+    at.write("-d=", "a:b:c\n");
+    at.write("--delimiter==", "x:y:z\n");
+    ucmd.args(&["-d:", "-f2", "--", "-d="])
+        .succeeds()
+        .stdout_only("b\n");
+}
+
 #[test]
 fn test_empty_string_as_delimiter() {
     new_ucmd!()