From 0e40a504077d53376bbcca34052df32175e47de5 Mon Sep 17 00:00:00 2001
From: Philipp Schuster <philipp.schuster@cyberus-technology.de>
Date: Mon, 19 May 2025 09:45:28 +0200
Subject: [PATCH] misc: option_parser: streamline #[source] and Error

This streamlines the code base to follow best practices for
error handling in Rust: Each error struct implements
std::error::Error (most due via thiserror::Error derive macro)
and sets its source accordingly.

This allows future work that nicely prints the error chains,
for example.

So far, the convention is that each error prints its
sub error as part of its Display::fmt() impl.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com
---
 Cargo.lock               |  3 +++
 option_parser/Cargo.toml |  3 +++
 option_parser/src/lib.rs | 24 ++++++++----------------
 3 files changed, 14 insertions(+), 16 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 2090d36d2..b7af3e20e 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1435,6 +1435,9 @@ checksum = "04744f49eae99ab78e0d5c0b603ab218f515ea8cfe5a456d7629ad883a3b6e7d"
 [[package]]
 name = "option_parser"
 version = "0.1.0"
+dependencies = [
+ "thiserror 2.0.6",
+]
 
 [[package]]
 name = "ordered-stream"
diff --git a/option_parser/Cargo.toml b/option_parser/Cargo.toml
index 23fbd4752..fc3129a70 100644
--- a/option_parser/Cargo.toml
+++ b/option_parser/Cargo.toml
@@ -3,3 +3,6 @@ authors = ["The Cloud Hypervisor Authors"]
 edition = "2021"
 name = "option_parser"
 version = "0.1.0"
+
+[dependencies]
+thiserror = "2.0.6"
diff --git a/option_parser/src/lib.rs b/option_parser/src/lib.rs
index 54f97ee29..2d4cce017 100644
--- a/option_parser/src/lib.rs
+++ b/option_parser/src/lib.rs
@@ -4,10 +4,11 @@
 //
 
 use std::collections::HashMap;
-use std::fmt;
 use std::num::ParseIntError;
 use std::str::FromStr;
 
+use thiserror::Error;
+
 #[derive(Default)]
 pub struct OptionParser {
     options: HashMap<String, OptionParserValue>,
@@ -18,26 +19,17 @@ struct OptionParserValue {
     requires_value: bool,
 }
 
-#[derive(Debug)]
+#[derive(Error, Debug)]
 pub enum OptionParserError {
+    #[error("unknown option: {0}")]
     UnknownOption(String),
+    #[error("unknown option: {0}")]
     InvalidSyntax(String),
-    Conversion(String, String),
+    #[error("unable to convert {1} for {0}")]
+    Conversion(String /* field */, String /* value */),
+    #[error("invalid value: {0}")]
     InvalidValue(String),
 }
-
-impl fmt::Display for OptionParserError {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        match self {
-            OptionParserError::UnknownOption(s) => write!(f, "unknown option: {s}"),
-            OptionParserError::InvalidSyntax(s) => write!(f, "invalid syntax:{s}"),
-            OptionParserError::Conversion(field, value) => {
-                write!(f, "unable to convert {value} for {field}")
-            }
-            OptionParserError::InvalidValue(s) => write!(f, "invalid value: {s}"),
-        }
-    }
-}
 type OptionParserResult<T> = std::result::Result<T, OptionParserError>;
 
 fn split_commas(s: &str) -> OptionParserResult<Vec<String>> {