echo: print help if not posixly corrent and only argument is --help

Author: RGBCube

Cargo.toml

@@ -626,7 +626,6 @@ unused_qualifications = "warn"
 all = { level = "warn", priority = -1 }
 cargo = { level = "warn", priority = -1 }
 pedantic = { level = "warn", priority = -1 }
-match_bool = "allow"                         # 8310
 cargo_common_metadata = "allow"              # 3240
 multiple_crate_versions = "allow"            # 2314
 missing_errors_doc = "allow"                 # 1504

src/uu/echo/src/echo.rs

@@ -99,7 +99,7 @@ fn is_flag(arg: &OsStr, options: &mut Options) -> bool {
 ///
 /// - Vector of non-flag arguments.
 /// - [`Options`], describing how teh arguments should be interpreted.
-fn filter_flags(mut args: impl uucore::Args) -> (Vec<OsString>, Options) {
+fn filter_flags(mut args: impl Iterator<Item = OsString>) -> (Vec<OsString>, Options) {
     let mut arguments = Vec::with_capacity(args.size_hint().0);
     let mut options = Options::default();
 
@@ -124,7 +124,7 @@ fn filter_flags(mut args: impl uucore::Args) -> (Vec<OsString>, Options) {
 #[uucore::main]
 pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     // args[0] is the name of the binary.
-    let mut args = args.skip(1).peekable();
+    let args: Vec<OsString> = args.skip(1).collect();
 
     // Check POSIX compatibility mode
     //
@@ -139,28 +139,36 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     // > representation. For example, echo -e '\x2dn'.
     let is_posixly_correct = env::var_os("POSIXLY_CORRECT").is_some();
 
-    let (args, options) = match is_posixly_correct {
-        // if POSIXLY_CORRECT is not set we filter the flags normally
-        false => filter_flags(args),
-
-        true if args.peek().is_some_and(|arg| arg == "-n") => {
+    let (args, options) = if is_posixly_correct {
+        if args.first().is_some_and(|arg| arg == "-n") {
             // if POSIXLY_CORRECT is set and the first argument is the "-n" flag
             // we filter flags normally but 'escaped' is activated nonetheless.
-            let (args, _) = filter_flags(args);
+            let (args, _) = filter_flags(args.into_iter());
             (
                 args,
                 Options {
                     trailing_newline: false,
                     ..Options::posixly_correct_default()
                 },
             )
-        }
-
-        true => {
+        } else {
             // if POSIXLY_CORRECT is set and the first argument is not the "-n" flag
-            // we just collect all arguments as every argument is considered an argument.
-            (args.collect(), Options::posixly_correct_default())
+            // we just collect all arguments as no arguments are interpreted as flags.
+            (args, Options::posixly_correct_default())
         }
+    } else if args.len() == 1 && args[0] == "--help" {
+        // If POSIXLY_CORRECT is not set and the first argument
+        // is `--help`, GNU coreutils prints the help message.
+        //
+        // Verify this using:
+        //
+        //   POSIXLY_CORRECT=1 echo --help
+        //                     echo --help
+        uu_app().print_help()?;
+        return Ok(());
+    } else {
+        // if POSIXLY_CORRECT is not set we filter the flags normally
+        filter_flags(args.into_iter())
     };
 
     execute(&mut io::stdout().lock(), args, options)?;

tests/by-util/test_echo.rs

@@ -514,6 +514,12 @@ fn partial_help_argument() {
     new_ucmd!().arg("--he").succeeds().stdout_is("--he\n");
 }
 
+#[test]
+fn only_help_argument_prints_help() {
+    assert_ne!(new_ucmd!().arg("--help").succeeds().stdout(), b"--help\n");
+    assert_ne!(new_ucmd!().arg("--help").succeeds().stdout(), b"--help"); // This one is just in case.
+}
+
 #[test]
 fn multibyte_escape_unicode() {
     // spell-checker:disable-next-line