More descriptive label for Source::Arith

"<arithmetic_expansion>" is no longer than "<command_substitution>", and
it is more descriptive than "<arith>".

yash-syntax/CHANGELOG.md

@@ -5,6 +5,13 @@ All notable changes to `yash-syntax` will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.10.1] - Unreleased
+
+### Changed
+
+- `source::Source::label` now returns `"<arithmetic_expansion>"` for
+  `Source::Arith`. Previously, it returned `"<arith>"`.
+
 ## [0.10.0] - 2024-07-12
 
 ### Added
@@ -282,6 +289,7 @@ command.
 - Functionalities to parse POSIX shell scripts
 - Alias substitution support
 
+[0.10.1]: https://github.com/magicant/yash-rs/releases/tag/yash-syntax-0.10.1
 [0.10.0]: https://github.com/magicant/yash-rs/releases/tag/yash-syntax-0.10.0
 [0.9.0]: https://github.com/magicant/yash-rs/releases/tag/yash-syntax-0.9.0
 [0.8.0]: https://github.com/magicant/yash-rs/releases/tag/yash-syntax-0.8.0

yash-syntax/src/source.rs

@@ -155,7 +155,7 @@ impl Source {
             CommandFile { path } => path,
             Alias { .. } => "<alias>",
             CommandSubst { .. } => "<command_substitution>",
-            Arith { .. } => "<arith>",
+            Arith { .. } => "<arithmetic_expansion>",
             Eval { .. } => "<eval>",
             DotScript { name, .. } => name,
             Trap { condition, .. } => condition,