cksum: print file name for explicit - operand

src/uu/checksum_common/src/lib.rs

@@ -10,6 +10,7 @@ use std::ffi::OsString;
 use std::io;
 
 use clap::builder::ValueParser;
+use clap::parser::ValueSource;
 use clap::{Arg, ArgAction, ArgMatches, Command, ValueHint};
 
 use uucore::checksum::compute::{
@@ -212,10 +213,13 @@ pub fn checksum_main(
     let algo = SizedAlgoKind::from_unsized(algo_kind, length)?;
     let line_ending = LineEnding::from_zero_flag(matches.get_flag(options::ZERO));
 
+    let has_file_operands = matches.value_source(options::FILE) == Some(ValueSource::CommandLine);
+
     let opts = ChecksumComputeOptions {
         algo_kind: algo,
         output_format,
         line_ending,
+        has_file_operands,
     };
 
     perform_checksum_computation(io::stdout(), opts, files)?;

src/uucore/src/lib/features/checksum/compute.rs

@@ -37,6 +37,11 @@ pub struct ChecksumComputeOptions {
 
     /// Whether to finish lines with '\n' or '\0'.
     pub line_ending: LineEnding,
+
+    /// Whether any file operand was given on the command line. GNU prints the
+    /// file name for an explicit "-" in legacy output, but not for the implicit
+    /// stdin used when no operand is provided.
+    pub has_file_operands: bool,
 }
 
 /// Whether to write the digest as hexadecimal or encoded in base64.
@@ -165,8 +170,9 @@ fn write_legacy_checksum(
         (algo, output) => unreachable!("Bug: Invalid legacy checksum ({algo:?}, {output:?})"),
     }
 
-    // Print the filename after a space if not stdin
-    if escaped_filename != "-" {
+    // Print the filename after a space if not stdin, unless a file operand
+    // was given explicitly.
+    if escaped_filename != "-" || options.has_file_operands {
         write!(w, " ")?;
         w.write_all(escaped_filename.as_bytes())?;
     }

tests/by-util/test_cksum.rs

@@ -89,6 +89,19 @@ fn test_stdin() {
         .stdout_is_fixture("crc_stdin.expected");
 }
 
+#[rstest]
+#[case::crc("crc", "4294967295 0 -\n")]
+#[case::bsd("bsd", "00000     0 -\n")]
+#[case::sysv("sysv", "0 0 -\n")]
+fn test_explicit_dash_prints_filename(#[case] algo: &str, #[case] expected: &str) {
+    new_ucmd!()
+        .args(&["--algorithm", algo, "-"])
+        .pipe_in(b"")
+        .succeeds()
+        .no_stderr()
+        .stdout_is(expected);
+}
+
 #[test]
 fn test_stdin_with_dash_directory() {
     let (at, mut ucmd) = at_and_ucmd!();