kernel_cmdline: convert to ThisError and sort

BUG=b:197143586
TEST=cargo check

Change-Id: Ic86f0d08b36e5f1b30ea35def38e3875c972c938
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/crosvm/+/3105081
Reviewed-by: Dennis Kempin <denniskempin@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
Commit-Queue: Daniel Verkamp <dverkamp@chromium.org>

Cargo.lock

@@ -609,6 +609,8 @@ name = "kernel_cmdline"
 version = "0.1.0"
 dependencies = [
  "libc",
+ "remain",
+ "thiserror",
 ]
 
 [[package]]

kernel_cmdline/Cargo.toml

@@ -5,6 +5,8 @@ edition = "2018"
 
 [dependencies]
 libc = "*"
+remain = "*"
+thiserror = "*"
 
 [lib]
 path = "src/kernel_cmdline.rs"

kernel_cmdline/src/kernel_cmdline.rs

@@ -4,37 +4,29 @@
 
 //! Helper for creating valid kernel command line strings.
 
-use std::fmt::{self, Display};
 use std::result;
 
+use remain::sorted;
+use thiserror::Error;
+
 /// The error type for command line building operations.
-#[derive(PartialEq, Debug)]
+#[sorted]
+#[derive(Error, PartialEq, Debug)]
 pub enum Error {
-    /// Operation would have resulted in a non-printable ASCII character.
-    InvalidAscii,
-    /// Key/Value Operation would have had a space in it.
-    HasSpace,
     /// Key/Value Operation would have had an equals sign in it.
+    #[error("string contains an equals sign")]
     HasEquals,
+    /// Key/Value Operation would have had a space in it.
+    #[error("string contains a space")]
+    HasSpace,
+    /// Operation would have resulted in a non-printable ASCII character.
+    #[error("string contains non-printable ASCII character")]
+    InvalidAscii,
     /// Operation would have made the command line too large.
+    #[error("inserting string would make command line too long")]
     TooLarge,
 }
 
-impl Display for Error {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        use self::Error::*;
-
-        let description = match self {
-            InvalidAscii => "string contains non-printable ASCII character",
-            HasSpace => "string contains a space",
-            HasEquals => "string contains an equals sign",
-            TooLarge => "inserting string would make command line too long",
-        };
-
-        write!(f, "{}", description)
-    }
-}
-
 /// Specialized Result type for command line operations.
 pub type Result<T> = result::Result<T, Error>;