1 files changed, 127 insertions, 0 deletions
diff --git a/src/derives/value_enum.rs b/src/derives/value_enum.rs
new file mode 100644
index 0000000..7a9d870
--- /dev/null
+++ b/src/derives/value_enum.rs
@@ -0,0 +1,127 @@
+// Copyright 2018 Guillaume Pinot (@TeXitoi) <texitoi@texitoi.eu>,
+// Kevin Knapp (@kbknapp) <kbknapp@gmail.com>, and
+// Ana Hobden (@hoverbear) <operator@hoverbear.org>
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+use proc_macro2::TokenStream;
+use proc_macro_error::{abort, abort_call_site};
+use quote::quote;
+use quote::quote_spanned;
+use syn::{spanned::Spanned, Data, DeriveInput, Fields, Ident, Variant};
+
+use crate::dummies;
+use crate::item::{Item, Kind, Name};
+
+pub fn derive_value_enum(input: &DeriveInput) -> TokenStream {
+    let ident = &input.ident;
+
+    dummies::value_enum(ident);
+
+    match input.data {
+        Data::Enum(ref e) => {
+            let name = Name::Derived(ident.clone());
+            let item = Item::from_value_enum(input, name);
+            let variants = e
+                .variants
+                .iter()
+                .map(|variant| {
+                    let item =
+                        Item::from_value_enum_variant(variant, item.casing(), item.env_casing());
+                    (variant, item)
+                })
+                .collect::<Vec<_>>();
+            gen_for_enum(&item, ident, &variants)
+        }
+        _ => abort_call_site!("`#[derive(ValueEnum)]` only supports enums"),
+    }
+}
+
+pub fn gen_for_enum(item: &Item, item_name: &Ident, variants: &[(&Variant, Item)]) -> TokenStream {
+    if !matches!(&*item.kind(), Kind::Value) {
+        abort! { item.kind().span(),
+            "`{}` cannot be used with `value`",
+            item.kind().name(),
+        }
+    }
+
+    let lits = lits(variants);
+    let value_variants = gen_value_variants(&lits);
+    let to_possible_value = gen_to_possible_value(item, &lits);
+
+    quote! {
+        #[allow(dead_code, unreachable_code, unused_variables, unused_braces)]
+        #[allow(
+            clippy::style,
+            clippy::complexity,
+            clippy::pedantic,
+            clippy::restriction,
+            clippy::perf,
+            clippy::deprecated,
+            clippy::nursery,
+            clippy::cargo,
+            clippy::suspicious_else_formatting,
+            clippy::almost_swapped,
+        )]
+        impl clap::ValueEnum for #item_name {
+            #value_variants
+            #to_possible_value
+        }
+    }
+}
+
+fn lits(variants: &[(&Variant, Item)]) -> Vec<(TokenStream, Ident)> {
+    variants
+        .iter()
+        .filter_map(|(variant, item)| {
+            if let Kind::Skip(_, _) = &*item.kind() {
+                None
+            } else {
+                if !matches!(variant.fields, Fields::Unit) {
+                    abort!(variant.span(), "`#[derive(ValueEnum)]` only supports unit variants. Non-unit variants must be skipped");
+                }
+                let fields = item.field_methods();
+                let deprecations = item.deprecations();
+                let name = item.cased_name();
+                Some((
+                    quote_spanned! { variant.span()=> {
+                        #deprecations
+                        clap::builder::PossibleValue::new(#name)
+                        #fields
+                    }},
+                    variant.ident.clone(),
+                ))
+            }
+        })
+        .collect::<Vec<_>>()
+}
+
+fn gen_value_variants(lits: &[(TokenStream, Ident)]) -> TokenStream {
+    let lit = lits.iter().map(|l| &l.1).collect::<Vec<_>>();
+
+    quote! {
+        fn value_variants<'a>() -> &'a [Self]{
+            &[#(Self::#lit),*]
+        }
+    }
+}
+
+fn gen_to_possible_value(item: &Item, lits: &[(TokenStream, Ident)]) -> TokenStream {
+    let (lit, variant): (Vec<TokenStream>, Vec<Ident>) = lits.iter().cloned().unzip();
+
+    let deprecations = item.deprecations();
+
+    quote! {
+        fn to_possible_value<'a>(&self) -> ::std::option::Option<clap::builder::PossibleValue> {
+            #deprecations
+            match self {
+                #(Self::#variant => Some(#lit),)*
+                _ => None
+            }
+        }
+    }
+}