narrative-macros 0.12.2

Procedural macros for the narrative crate
Documentation 
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// Separation of impls and assertions leads not only simple implementation but also good error
// messages that indicate an outer dependency.
mod local_type_assertions;
mod local_type_impls;

mod base_trait;
mod step_fn;
mod story_trait;

mod step_args;
mod step_types;
mod story_consts;
mod story_context;

mod dummy_environment;

use proc_macro2::TokenStream;
use quote::{format_ident, quote, ToTokens};

use crate::{item_story::ItemStory, story_attr_syntax::StoryAttr, Asyncness};

pub(crate) fn generate(attr: &StoryAttr, item: &ItemStory) -> TokenStream {
    let mod_ident = format_ident!("mod_{}", item.ident);
    let ident = &item.ident;
    let async_ident = format_ident!("Async{}", item.ident);
    let context_ident = format_ident!("{}Context", item.ident);
    let base_trait = base_trait::generate(item, Asyncness::Sync);
    let async_base_trait = base_trait::generate(item, Asyncness::Async);
    let story_trait = story_trait::generate(item, Asyncness::Sync);
    let async_story_trait = story_trait::generate(item, Asyncness::Async);
    let step_args = step_args::generate(item);
    let step_types = step_types::generate(item);
    let story_consts = story_consts::generate(item);
    let story_context = story_context::generate(attr, item);
    let context_ext = story_context::generate_ext(item);
    let local_type_impls = local_type_impls::generate(item);
    let local_type_assertions = local_type_assertions::generate(item);
    let dummy_environment = dummy_environment::generate(item, Asyncness::Sync);
    let async_dummy_environment = dummy_environment::generate(item, Asyncness::Async);
    let local_type_trait = format_ident!("{}LocalType", ident);
    quote! {
        #[allow(non_snake_case, unused_imports)]
        mod #mod_ident {
            use super::*;
            #base_trait
            #async_base_trait
            #story_trait
            #async_story_trait
            #step_args
            #step_types
            #story_consts
            #story_context
            #context_ext
            #local_type_impls
            #local_type_assertions
            #dummy_environment
            #async_dummy_environment
        }
        #[allow(unused_imports)]
        use narrative::prelude::*;
        #[allow(unused_imports)]
        pub use #mod_ident::#ident;
        #[allow(unused_imports)]
        pub use #mod_ident::#async_ident;
        #[allow(unused_imports)]
        pub use #mod_ident::StoryContext as #context_ident;
        #[allow(unused_imports)]
        pub use #mod_ident::#local_type_trait;
        pub use #mod_ident::ContextExt as _;
        pub use #mod_ident::AsyncContextExt as _;
        pub use #mod_ident::BaseTrait as _;
    }
}

#[derive(Default)]
struct MatchArms {
    arms: Vec<TokenStream>,
    cast_as: Option<TokenStream>,
    match_target: Option<TokenStream>,
    fallback: Option<TokenStream>,
}

impl MatchArms {
    pub fn cast_as(mut self, cast_as: TokenStream) -> Self {
        self.cast_as = Some(cast_as);
        self
    }

    pub fn match_target(mut self, match_target: TokenStream) -> Self {
        self.match_target = Some(match_target);
        self
    }
}
impl FromIterator<TokenStream> for MatchArms {
    fn from_iter<T: IntoIterator<Item = TokenStream>>(iter: T) -> Self {
        Self {
            arms: iter.into_iter().collect(),
            ..Default::default()
        }
    }
}

impl<'a> FromIterator<&'a TokenStream> for MatchArms {
    fn from_iter<T: IntoIterator<Item = &'a TokenStream>>(iter: T) -> Self {
        Self {
            arms: iter.into_iter().cloned().collect(),
            ..Default::default()
        }
    }
}

impl ToTokens for MatchArms {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        let extend = if self.arms.is_empty() {
            if let Some(cast_as) = &self.cast_as {
                quote! {
                    #[allow(unreachable_code)]
                    {
                        unreachable!() as #cast_as
                    }
                }
            } else {
                quote! {
                    unreachable!()
                }
            }
        } else {
            let arms = &self.arms;
            let match_target = self.match_target.clone().unwrap_or_else(|| quote!(self));
            let fallback = self.fallback.as_ref().map(|fallback| {
                quote! {
                    _ => #fallback,
                }
            });
            quote! {
                match #match_target {
                    #(#arms)*
                    #fallback
                }
            }
        };
        tokens.extend(::core::iter::once(extend));
    }
}