Fix printf infinite loop

src/uu/printf/src/printf.rs

@@ -6,12 +6,13 @@
 // spell-checker:ignore (change!) each's
 // spell-checker:ignore (ToDO) LONGHELP FORMATSTRING templating parameterizing formatstr
 
-use std::io::stdout;
+use std::io::{stdout, Write};
 use std::ops::ControlFlow;
 
 use clap::{crate_version, Arg, ArgAction, Command};
-use uucore::error::{UResult, UUsageError};
-use uucore::format::{parse_spec_and_escape, FormatArgument};
+use uucore::display::Quotable;
+use uucore::error::{UResult, USimpleError, UUsageError};
+use uucore::format::{parse_spec_and_escape, ArgumentIter, FormatArgument};
 use uucore::{format_usage, help_about, help_section, help_usage};
 
 const VERSION: &str = "version";
@@ -39,13 +40,26 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
     };
 
     let mut args = values.iter().peekable();
+    let first_arg = args.peek().cloned();
     for item in parse_spec_and_escape(format_string.as_ref()) {
         match item?.write(stdout(), &mut args)? {
             ControlFlow::Continue(()) => {}
             ControlFlow::Break(()) => return Ok(()),
         };
     }
 
+    if let Some(arg) = args.peek() {
+        // Check if no arguments were used while parsing the format.
+        if Some(arg) == first_arg.as_ref() {
+            stdout().flush()?;
+            let warning_message = format!(
+                "warning: ignoring excess arguments, starting with {}",
+                args.get_str().quote()
+            );
+            return Err(USimpleError::new(0, warning_message.as_str()));
+        }
+    }
+
     while args.peek().is_some() {
         for item in parse_spec_and_escape(format_string.as_ref()) {
             match item?.write(stdout(), &mut args)? {
@@ -54,6 +68,7 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
             };
         }
     }
+
     Ok(())
 }
 

src/uucore/src/lib/features/format/argument.rs

@@ -14,7 +14,7 @@ use crate::{error::set_exit_code, show_warning};
 ///
 /// The [`FormatArgument::Unparsed`] variant contains a string that can be
 /// parsed into other types. This is used by the `printf` utility.
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, PartialEq)]
 pub enum FormatArgument {
     Char(char),
     String(String),

tests/by-util/test_printf.rs

@@ -72,6 +72,15 @@ fn escaped_unrecognized() {
     new_ucmd!().args(&["c\\d"]).succeeds().stdout_only("c\\d");
 }
 
+#[test]
+fn ignore_excess_arguments() {
+    new_ucmd!()
+        .args(&["a", "b"])
+        .succeeds()
+        .stdout_is("a")
+        .stderr_is("printf: warning: ignoring excess arguments, starting with 'b'\n");
+}
+
 #[test]
 fn sub_string() {
     new_ucmd!()