xargs: treat whitespace-only input as no argument (fixes #771)

src/xargs/mod.rs

@@ -605,7 +605,13 @@ where
                             format!("Unterminated quote: {q}"),
                         ));
                     }
-                    if i == 0 {
+                    // Input that consists only of delimiters (whitespace)
+                    // produces no argument — a run of delimiters with no
+                    // content between them yields nothing, matching GNU xargs.
+                    // `i == 0` handles the case where we read no bytes at all;
+                    // `result.is_empty()` additionally covers input we consumed
+                    // but that was pure whitespace.
+                    if result.is_empty() {
                         return Ok(None);
                     }
                     pending.clear();

tests/test_xargs.rs

@@ -73,6 +73,50 @@ fn xargs_if_empty() {
     ucmd().args(&["--no-run-if-empty"]).succeeds().no_output();
 }
 
+#[test]
+fn xargs_whitespace_only_input() {
+    // Input that consists only of delimiters (whitespace) produces no
+    // argument, matching GNU xargs: a run of delimiters with no content
+    // between them yields no argument. The command still runs once with no
+    // extra args (the default, as with empty input).
+    ucmd().pipe_in(" ").succeeds().no_stderr().stdout_only("\n");
+
+    // Other ASCII whitespace should behave the same as a space.
+    ucmd()
+        .pipe_in("\t")
+        .succeeds()
+        .no_stderr()
+        .stdout_only("\n");
+    ucmd()
+        .pipe_in(" \t\n \n")
+        .succeeds()
+        .no_stderr()
+        .stdout_only("\n");
+
+    // With --no-run-if-empty, whitespace-only input means nothing to do.
+    ucmd()
+        .args(&["--no-run-if-empty"])
+        .pipe_in(" ")
+        .succeeds()
+        .no_output();
+
+    // The same holds when reading from a file with -a (issue #771 repro):
+    // the child must receive zero arguments, not an empty-string argument.
+    let temp_file = tempfile::NamedTempFile::new().unwrap();
+    std::fs::write(temp_file.path(), b" ").unwrap();
+    let result = ucmd()
+        .args(&[
+            "-a",
+            &temp_file.path().to_string_lossy(),
+            &path_to_testing_commandline(),
+            "-",
+            "--no_print_cwd",
+        ])
+        .succeeds();
+    result.no_stderr();
+    assert_eq!(result.stdout_str(), "args=\n--no_print_cwd\n");
+}
+
 #[test]
 fn xargs_replace_empty_input() {
     ucmd()