Fixed an issue in parsing of EngineKind

`--engine` was not getting correctly parsed as `EngineKind` but was
getting parsed as a `String`. This was happening because `value_parser`
set initially was getting overwritten (in the original code).

This caused a runtime `panic!`. Fixed, works properly.

Signed-off-by: Abhijit Gadgil <[email protected]>

components/pkg-export-container/src/engine.rs

@@ -56,7 +56,7 @@ enum EngineError {
 /// When https://github.com/containers/buildah/issues/2215 is fixed,
 /// we can update our Buildah dependency and remove this check.
 pub fn fail_if_buildah_and_multilayer(matches: &ArgMatches) -> Result<()> {
-    if matches.get_one::<String>("ENGINE") == Some(&"buildah".to_owned())
+    if matches.get_one::<EngineKind>("ENGINE") == Some(&EngineKind::Buildah)
        && matches.get_flag("MULTI_LAYER")
     {
         return Err(EngineError::BuildahIncompatibleWithMultiLayer.into());
@@ -65,7 +65,7 @@ pub fn fail_if_buildah_and_multilayer(matches: &ArgMatches) -> Result<()> {
 }
 
 /// Things that can build containers!
-#[derive(Clone, Copy, Debug, Default, clap::ValueEnum)]
+#[derive(Clone, Copy, Debug, Default, PartialEq, Eq, clap::ValueEnum)]
 enum EngineKind {
     #[default]
     Docker,
@@ -116,8 +116,7 @@ pub fn cli_arg() -> Arg {
         // Since there is effectively no choice of engine for
         // Windows, we hide the CLI option and don't document it
         // any further.
-        arg.value_parser(["docker"])
-            .hide(true)
+        arg.hide(true)
     } else {
         arg.long_help(
 "Using the `docker` engine allows you to use Docker to create
@@ -135,16 +134,14 @@ Please see https://buildah.io for more details.
 Both engines create equivalent container images.
 ",
         )
-            .value_parser(["docker", "buildah"])
     }
 }
 
 impl TryFrom<&ArgMatches> for Box<dyn Engine> {
     type Error = anyhow::Error;
 
     fn try_from(value: &ArgMatches) -> StdResult<Self, Self::Error> {
-        let engine = value.get_one::<String>("ENGINE").unwrap();
-        let engine = EngineKind::from_str(engine).unwrap();
+        let engine = value.get_one::<EngineKind>("ENGINE").unwrap();
         match engine {
             EngineKind::Docker => Ok(Box::new(docker::DockerEngine::new()?)),
             #[cfg(not(windows))]