fix(derive): Abort on non-unit variant

clap_derive/src/derives/arg_enum.rs

@@ -35,7 +35,7 @@ pub fn derive_arg_enum(input: &DeriveInput) -> TokenStream {
 
 pub fn gen_for_enum(name: &Ident, attrs: &[Attribute], e: &DataEnum) -> TokenStream {
     if !e.variants.iter().all(|v| matches!(v.fields, Fields::Unit)) {
-        return quote!();
+        abort_call_site!("`#[derive(ArgEnum)]` only supports non-unit variants");
     };
 
     let attrs = Attrs::from_struct(

examples/derive_ref/README.md

@@ -82,6 +82,7 @@ fn main() {
 - `Subcommand` defines available subcommands.
   - Subcommand arguments can be defined in a struct-variant or automatically flattened with a tuple-variant.
 - `ArgEnum` allows parsing a value directly into an `enum`, erroring on unsupported values.
+  - The derive doesn't work on enums that contain non-unit variants
 
 See also the [tutorial](../tutorial_derive/README.md) and [examples](../README.md).
 

tests/derive_ui/arg_enum_non_unit.rs

@@ -0,0 +1,10 @@
+use clap::ArgEnum;
+
+#[derive(ArgEnum, Clone, Debug)]
+enum Opt {
+    Foo(usize),
+}
+
+fn main() {
+    println!("{:?}", Opt::Foo(42));
+}

tests/derive_ui/arg_enum_non_unit.stderr

@@ -0,0 +1,7 @@
+error: `#[derive(ArgEnum)]` only supports non-unit variants
+ --> tests/derive_ui/arg_enum_non_unit.rs:3:10
+  |
+3 | #[derive(ArgEnum, Clone, Debug)]
+  |          ^^^^^^^
+  |
+  = note: this error originates in the derive macro `ArgEnum` (in Nightly builds, run with -Z macro-backtrace for more info)