implement enum variant generation

src/lib.rs

@@ -2,12 +2,41 @@
 //! extra information about the field.
 
 use darling::{util::PathList, FromMeta};
+use parser::Enum;
 use proc_macro::TokenStream;
 use quote::quote;
 use syn::{parse_macro_input, parse_quote, DataStruct, DeriveInput};
 
 mod parser;
 
+/// Implements `miniconf::Tree` for the given enum.
+///
+/// This implementation of `miniconf::Tree` adds a value and a variants path.
+/// The value path serializes the enum.
+/// The variants path serializes all possible variants as an array.
+/// Optionally default and description paths can be generated.
+/// The description is generated from the docstring describing the enum.
+///
+/// # Example
+/// ```
+/// use macroconf::ConfigEnum;
+/// use serde::{Serialize, Deserialize};
+///
+/// /// Description
+/// #[derive(Default, ConfigEnum, Serialize, Deserialize)]
+/// enum Test {
+///     #[default]
+///     Variant1,
+///     Variant2,
+///     Variant3,
+/// }
+/// ```
+#[proc_macro_derive(ConfigEnum, attributes(default))]
+pub fn config_enum(item: TokenStream) -> TokenStream {
+    let input = parse_macro_input!(item as Enum);
+    input.generate_tree().into()
+}
+
 /// Creates structs for the values to extend them with extra metadata.
 ///
 /// supported metadata is `min`, `max` and `default`. Doc comments are parsed as `description`

src/parser.rs

@@ -10,7 +10,7 @@ use darling::{
 };
 use proc_macro2::{Span, TokenStream};
 use quote::{format_ident, quote};
-use syn::{parse_quote, spanned::Spanned};
+use syn::{braced, parse::Parse, parse_quote, spanned::Spanned, Token};
 
 #[derive(Debug, FromField)]
 #[darling(attributes(config))]
@@ -515,3 +515,256 @@ impl Config {
         &mut fields.fields
     }
 }
+
+#[derive(Debug, PartialEq, Eq, Clone)]
+pub struct Enum {
+    doc: Option<String>,
+    ident: syn::Ident,
+    variants: Vec<syn::Ident>,
+    default: Option<syn::Ident>,
+}
+
+impl Enum {
+    pub fn generate_tree(&self) -> TokenStream {
+        let mut tokens = self.generate_tree_key();
+        tokens.extend(self.generate_tree_serialize());
+        tokens.extend(self.generate_tree_deserialize());
+        tokens.extend(self.generate_tree_any());
+        tokens
+    }
+
+    fn keys(&self) -> Vec<(&'static str, syn::Expr)> {
+        let variants = &self.variants;
+        let mut keys = vec![
+            ("value", parse_quote!(self)),
+            ("variants", parse_quote!([#(Self::#variants,)*])),
+        ];
+        if let Some(ref doc) = self.doc {
+            keys.push(("description", parse_quote!(#doc)));
+        }
+        if let Some(ref default) = self.default {
+            keys.push(("default", parse_quote!(Self::#default)));
+        }
+        keys
+    }
+
+    fn generate_tree_key(&self) -> TokenStream {
+        let ident = &self.ident;
+        let keys = self.keys();
+        let num_keys = keys.len();
+        let max_length = keys.iter().map(|(path, _)| path.len()).max();
+        let keys = keys.iter().map(|(path, _)| path);
+        quote! {
+            impl ::miniconf::KeyLookup for #ident {
+                const LEN: usize = #num_keys;
+                const NAMES: &'static [&'static str] = &[#(#keys,)*];
+
+                fn name_to_index(value: &str) -> Option<usize> {
+                    Self::NAMES.iter().position(|name| *name == value)
+                }
+            }
+
+            impl ::miniconf::TreeKey<1> for #ident {
+                fn metadata() -> ::miniconf::Metadata {
+                    let mut metadata = ::miniconf::Metadata::default();
+                    metadata.max_depth = 1;
+                    metadata.count = #num_keys;
+                    metadata.max_length = #max_length;
+                    metadata
+                }
+
+                fn traverse_by_key<K, F, E>(mut keys: K, mut func: F) -> ::core::result::Result<usize, ::miniconf::Error<E>>
+                where
+                    K: ::miniconf::Keys,
+                    // Writing this to return an iterator instead of using a callback
+                    // would have worse performance (O(n^2) instead of O(n) for matching)
+                    F: FnMut(usize, Option<&'static str>, usize) -> ::core::result::Result<(), E>,
+                {
+                    let ::core::result::Result::Ok(key) = keys.next::<Self>() else { return ::core::result::Result::Ok(0) };
+                    let index = ::miniconf::Key::find::<Self>(&key).ok_or(::miniconf::Traversal::NotFound(1))?;
+                    let name = <Self as ::miniconf::KeyLookup>::NAMES
+                        .get(index)
+                        .ok_or(::miniconf::Traversal::NotFound(1))?;
+                    func(index, Some(name), #num_keys).map_err(|err| ::miniconf::Error::Inner(1, err))?;
+                    ::core::result::Result::Ok(1)
+                }
+            }
+        }
+    }
+
+    fn generate_tree_serialize(&self) -> TokenStream {
+        let ident = &self.ident;
+        let matches = self
+            .keys()
+            .iter()
+            .enumerate()
+            .map(|(i, (_, expr))| {
+                quote! {
+                    #i => ::serde::Serialize::serialize(&#expr, ser).map_err(|err| ::miniconf::Error::Inner(0, err)),
+                }
+            })
+            .collect::<Vec<_>>();
+        quote! {
+            impl ::miniconf::TreeSerialize<1> for #ident {
+                fn serialize_by_key<K, S>(
+                    &self,
+                    mut keys: K,
+                    ser: S,
+                ) -> ::core::result::Result<usize, ::miniconf::Error<S::Error>>
+                where
+                    K: ::miniconf::Keys,
+                    S: ::serde::Serializer,
+                {
+                    let ::core::result::Result::Ok(key) = keys.next::<Self>() else {
+                        return ::serde::Serialize::serialize(self, ser).map_err(|err| ::miniconf::Error::Inner(0, err)).map(|_| 0);
+                    };
+                    let index = ::miniconf::Key::find::<Self>(&key).ok_or(::miniconf::Traversal::NotFound(0))?;
+                    if !keys.finalize() {
+                        return ::core::result::Result::Err(::miniconf::Traversal::TooLong(0).into());
+                    }
+                    match index {
+                        #(#matches)*
+                        _ => unreachable!(),
+                    }?;
+                    Ok(0)
+                }
+            }
+        }
+    }
+
+    fn generate_tree_deserialize(&self) -> TokenStream {
+        let ident = &self.ident;
+        let num_keys = self.keys().len();
+        quote! {
+            impl<'de> ::miniconf::TreeDeserialize<'de, 1> for #ident {
+                fn deserialize_by_key<K, D>(
+                    &mut self,
+                    mut keys: K,
+                    de: D,
+                ) -> ::core::result::Result<usize, ::miniconf::Error<D::Error>>
+                where
+                    K: ::miniconf::Keys,
+                    D: ::serde::Deserializer<'de>,
+                {
+                    let ::core::result::Result::Ok(key) = keys.next::<Self>() else {
+                        <Self as ::serde::Deserialize>::deserialize(de).map_err(|err| ::miniconf::Error::Inner(0, err))?;
+                        return ::core::result::Result::Ok(0);
+                    };
+                    let index = ::miniconf::Key::find::<Self>(&key).ok_or(::miniconf::Traversal::NotFound(1))?;
+                    if !keys.finalize() {
+                        return ::core::result::Result::Err(::miniconf::Traversal::TooLong(1).into());
+                    }
+                    match index {
+                        0 => {
+                            <Self as ::serde::Deserialize>::deserialize(de).map_err(|err| ::miniconf::Error::Inner(0, err))?;
+                            Ok(0)
+                        }
+                        1..=#num_keys => ::core::result::Result::Err(::miniconf::Traversal::Access(0, "Cannot write limits").into()),
+                        _ => unreachable!(),
+                    }
+                }
+            }
+        }
+    }
+
+    fn generate_tree_any(&self) -> TokenStream {
+        let ident = &self.ident;
+        let num_keys = self.keys().len();
+        quote! {
+            impl ::miniconf::TreeAny<1> for #ident {
+                fn ref_any_by_key<K>(&self, mut keys: K) -> ::core::result::Result<&dyn ::core::any::Any, ::miniconf::Traversal>
+                where
+                    K: ::miniconf::Keys,
+                {
+                    let ::core::result::Result::Ok(key) = keys.next::<Self>() else {
+                        return ::core::result::Result::Ok(self);
+                    };
+                    let index = ::miniconf::Key::find::<Self>(&key).ok_or(::miniconf::Traversal::NotFound(1))?;
+                    if !keys.finalize() {
+                        return ::core::result::Result::Err(::miniconf::Traversal::TooLong(1));
+                    }
+                    match index {
+                        0 => ::core::result::Result::Ok(self),
+                        1..#num_keys => ::core::result::Result::Err(::miniconf::Traversal::Access(1, "cannot return reference to local variable")),
+                        _ => unreachable!(),
+                    }
+                }
+
+                fn mut_any_by_key<K>(&mut self, mut keys: K) -> ::core::result::Result<&mut dyn ::core::any::Any, ::miniconf::Traversal>
+                where
+                    K: ::miniconf::Keys,
+                {
+                    let ::core::result::Result::Ok(key) = keys.next::<Self>() else {
+                        return Ok(self);
+                    };
+                    let index = ::miniconf::Key::find::<Self>(&key).ok_or(::miniconf::Traversal::NotFound(1))?;
+                    if !keys.finalize() {
+                        return ::core::result::Result::Err(::miniconf::Traversal::TooLong(1));
+                    }
+                    match index {
+                        0 => Ok(self),
+                        1..#num_keys => ::core::result::Result::Err(::miniconf::Traversal::Access(1, "cannot return reference to local variable")),
+                        _ => unreachable!(),
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl Parse for Enum {
+    fn parse(input: syn::parse::ParseStream) -> syn::Result<Self> {
+        let attrs = input.call(syn::Attribute::parse_outer)?;
+        let doc = attrs
+            .iter()
+            .find(|attr| attr.path().is_ident("doc"))
+            .map(|attr| {
+                let meta = attr.meta.require_name_value()?;
+                if let syn::Expr::Lit(syn::ExprLit {
+                    attrs: _,
+                    lit: syn::Lit::Str(ref lit),
+                }) = meta.value
+                {
+                    Ok(lit.value().trim().to_owned())
+                } else {
+                    Err(syn::Error::new_spanned(
+                        &meta.value,
+                        "Expected string literal for doc comment",
+                    ))
+                }
+            })
+            .transpose()?;
+
+        let _vis = input.parse::<syn::Visibility>()?;
+        let _enum_token = input.parse::<Token![enum]>()?;
+
+        let ident = input.parse::<syn::Ident>()?;
+
+        let content;
+        let _brace = braced!(content in input);
+        let variants = content.parse_terminated(syn::Variant::parse, Token![,])?;
+        if let Some(variant) = variants.iter().find(|variant| !variant.fields.is_empty()) {
+            return Err(syn::Error::new_spanned(
+                &variant.fields,
+                "only unit variants are supported for now",
+            ));
+        }
+        let default = variants
+            .iter()
+            .find(|variant| {
+                variant
+                    .attrs
+                    .iter()
+                    .any(|attr| attr.path().is_ident("default"))
+            })
+            .map(|variant| variant.ident.clone());
+        let variants = variants.into_iter().map(|variant| variant.ident).collect();
+
+        Ok(Self {
+            doc,
+            ident,
+            variants,
+            default,
+        })
+    }
+}