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//! Helper functions for writing redacted strings.
use std::fmt;
/// Write up to `chars` _characters_ from the start of `input` onto `f`.
///
/// If any characters are removed, replace them with `ellipsis`.
pub fn write_start_redacted(
f: &mut fmt::Formatter,
input: &str,
chars: usize,
ellipsis: &str,
) -> fmt::Result {
if let Some((pos, _)) = input.char_indices().nth(chars) {
let slice = input
.get(..pos)
.expect("Mismatched character offset calculation");
write!(f, "{slice}{ellipsis}")
} else {
write!(f, "{input}")
}
/// Write up to `chars` _characters_ from the end of `input` onto `f`.
pub fn write_end_redacted(
if chars == 0 {
if input.is_empty() {
Ok(())
write!(f, "{ellipsis}")
} else if let Some((pos, _)) = input.char_indices().nth_back(chars - 1)
&& pos != 0
{
.get(pos..)
write!(f, "{ellipsis}{slice}")
#[cfg(test)]
mod test {
// @@ begin test lint list maintained by maint/add_warning @@
#![allow(clippy::bool_assert_comparison)]
#![allow(clippy::clone_on_copy)]
#![allow(clippy::dbg_macro)]
#![allow(clippy::mixed_attributes_style)]
#![allow(clippy::print_stderr)]
#![allow(clippy::print_stdout)]
#![allow(clippy::single_char_pattern)]
#![allow(clippy::unwrap_used)]
#![allow(clippy::unchecked_time_subtraction)]
#![allow(clippy::useless_vec)]
#![allow(clippy::needless_pass_by_value)]
#![allow(clippy::string_slice)] // See arti#2571
//! <!-- @@ end test lint list maintained by maint/add_warning @@ -->
use super::*;
struct Fmt<'a> {
string: &'a str,
n: usize,
start: bool,
impl<'a> fmt::Display for Fmt<'a> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
if self.start {
write_start_redacted(f, self.string, self.n, "…")
write_end_redacted(f, self.string, self.n, "…")
fn rstart(string: &str, n: usize) -> String {
Fmt {
string,
n,
start: true,
.to_string()
fn rend(string: &str, n: usize) -> String {
start: false,
#[test]
fn test_redact_start() {
assert_eq!(&rstart("hello world", 2), "he…");
assert_eq!(&rstart("he", 2), "he");
assert_eq!(&rstart("h", 2), "h");
assert_eq!(&rstart("", 2), "");
assert_eq!(&rstart("", 0), "");
assert_eq!(&rstart("hello", 0), "…");
assert_eq!(&rstart("分久必合，合久必分", 2), "分久…");
assert_eq!(&rstart("分久必合，合久必分", 4), "分久必合…");
assert_eq!(&rstart("分久必合，合久必分", 9), "分久必合，合久必分");
assert_eq!(&rstart("分久必合，合久必分", 10), "分久必合，合久必分");
assert_eq!(&rstart("分久必合，合久必分", 0), "…");
fn test_redact_end() {
assert_eq!(&rend("hello world", 2), "…ld");
assert_eq!(&rend("he", 2), "he");
assert_eq!(&rend("h", 2), "h");
assert_eq!(&rend("", 2), "");
assert_eq!(&rend("", 0), "");
assert_eq!(&rend("hello", 0), "…");
assert_eq!(&rend("分久必合，合久必分", 2), "…必分");
assert_eq!(&rend("分久必合，合久必分", 4), "…合久必分");
assert_eq!(&rend("分久必合，合久必分", 9), "分久必合，合久必分");
assert_eq!(&rend("分久必合，合久必分", 10), "分久必合，合久必分");
assert_eq!(&rend("分久必合，合久必分", 0), "…");