xargs: print help/version without error prefix

xargs, when executed with -h/--help or -V/--version, is printing an
"Error: " prefix before the help and version text. The exit code is
also incorrect (1, instead of 0).

Display the help/version text without the erroneous prefix, and exit
with the correct exit code (success, 0).

Add tests for this bug to prevent regressions.

src/xargs/mod.rs

@@ -14,7 +14,7 @@ use std::{
     process::{Command, Stdio},
 };
 
-use clap::{crate_version, Arg, ArgAction};
+use clap::{crate_version, error::ErrorKind, Arg, ArgAction};
 
 mod options {
     pub const COMMAND: &str = "COMMAND";
@@ -954,7 +954,15 @@ fn do_xargs(args: &[&str]) -> Result<CommandResult, XargsError> {
 
     let matches = match matches {
         Ok(m) => m,
-        Err(e) => return Err(XargsError::from(e.to_string())),
+        Err(e) => match e.kind() {
+            ErrorKind::DisplayHelp | ErrorKind::DisplayVersion => {
+                // The help/version text already has a newline, so use `print!` here, not `println!`
+                print!("{e}");
+
+                return Ok(CommandResult::Success);
+            }
+            _ => return Err(XargsError::from(e.to_string())),
+        },
     };
 
     let options = Options {

tests/xargs_tests.rs

@@ -564,3 +564,37 @@ fn xargs_replace_multiple_lines() {
         .stderr(predicate::str::is_empty())
         .stdout(predicate::str::diff("\n\n\n"));
 }
+
+#[test]
+fn xargs_help() {
+    for option_style in ["-h", "--help"] {
+        Command::cargo_bin("xargs")
+            .expect("found binary")
+            .args([option_style])
+            .assert()
+            .success()
+            .code(0)
+            .stderr(predicate::str::is_empty())
+            .stdout(predicate::str::contains("Usage: xargs "));
+    }
+}
+
+// Do not regress to:
+//
+// ❯ xargs --version
+// Error: xargs 0.7.0
+//
+// Same for help above
+#[test]
+fn xargs_version() {
+    for option_style in ["-V", "--version"] {
+        Command::cargo_bin("xargs")
+            .expect("found binary")
+            .args([option_style])
+            .assert()
+            .success()
+            .code(0)
+            .stderr(predicate::str::is_empty())
+            .stdout(predicate::str::starts_with("xargs "));
+    }
+}