unexpand: move to thiserror

Cargo.lock

@@ -3415,6 +3415,7 @@ name = "uu_unexpand"
 version = "0.0.30"
 dependencies = [
  "clap",
+ "thiserror 2.0.12",
  "unicode-width 0.2.0",
  "uucore",
 ]

src/uu/unexpand/Cargo.toml

@@ -17,6 +17,7 @@ readme.workspace = true
 path = "src/unexpand.rs"
 
 [dependencies]
+thiserror = { workspace = true }
 clap = { workspace = true }
 unicode-width = { workspace = true }
 uucore = { workspace = true }

src/uu/unexpand/src/unexpand.rs

@@ -6,13 +6,12 @@
 // spell-checker:ignore (ToDO) nums aflag uflag scol prevtab amode ctype cwidth nbytes lastcol pctype Preprocess
 
 use clap::{Arg, ArgAction, Command};
-use std::error::Error;
-use std::fmt;
 use std::fs::File;
 use std::io::{BufRead, BufReader, BufWriter, Read, Stdout, Write, stdin, stdout};
 use std::num::IntErrorKind;
 use std::path::Path;
 use std::str::from_utf8;
+use thiserror::Error;
 use unicode_width::UnicodeWidthChar;
 use uucore::display::Quotable;
 use uucore::error::{FromIo, UError, UResult, USimpleError};
@@ -23,30 +22,20 @@ const ABOUT: &str = help_about!("unexpand.md");
 
 const DEFAULT_TABSTOP: usize = 8;
 
-#[derive(Debug)]
+#[derive(Debug, Error)]
 enum ParseError {
+    #[error("tab size contains invalid character(s): {}", _0.quote())]
     InvalidCharacter(String),
+    #[error("tab size cannot be 0")]
     TabSizeCannotBeZero,
+    #[error("tab stop value is too large")]
     TabSizeTooLarge,
+    #[error("tab sizes must be ascending")]
     TabSizesMustBeAscending,
 }
 
-impl Error for ParseError {}
 impl UError for ParseError {}
 
-impl fmt::Display for ParseError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            Self::InvalidCharacter(s) => {
-                write!(f, "tab size contains invalid character(s): {}", s.quote())
-            }
-            Self::TabSizeCannotBeZero => write!(f, "tab size cannot be 0"),
-            Self::TabSizeTooLarge => write!(f, "tab stop value is too large"),
-            Self::TabSizesMustBeAscending => write!(f, "tab sizes must be ascending"),
-        }
-    }
-}
-
 fn tabstops_parse(s: &str) -> Result<Vec<usize>, ParseError> {
     let words = s.split(',');