action_derive/

lib.rs

#![allow(clippy::missing_panics_doc)]

mod ident;
mod manifest;

use manifest::Manifest;
use proc_macro2::TokenStream;
use quote::quote;
use std::path::{Path, PathBuf};

fn resolve_path(path: impl AsRef<Path>) -> PathBuf {
    let root = PathBuf::from(std::env::var("CARGO_MANIFEST_DIR").unwrap_or_else(|_| ".".into()));
    if root.join(path.as_ref()).exists() {
        root.join(path.as_ref())
    } else {
        root.join("src/").join(path.as_ref())
    }
}

fn quote_option<T: quote::ToTokens>(value: Option<&T>) -> TokenStream {
    if let Some(v) = value {
        quote! { Some(#v) }
    } else {
        quote! { None }
    }
}

fn get_attribute(attr: &syn::Attribute) -> String {
    match &attr.meta {
        syn::Meta::NameValue(syn::MetaNameValue { path, value, .. }) => {
            debug_assert!(path.is_ident("action"));
            match value {
                syn::Expr::Lit(syn::ExprLit {
                    lit: syn::Lit::Str(s),
                    ..
                }) => s.value(),
                _ => panic!("action attribute must be a literal string"),
            }
        }
        _ => panic!(r#"action attribute must be of the form `action = "..."`"#),
    }
}

fn parse_derive(ast: &syn::DeriveInput) -> (&syn::Ident, &syn::Generics, PathBuf) {
    let name = &ast.ident;
    let generics = &ast.generics;

    let manifests: Vec<_> = ast
        .attrs
        .iter()
        .filter(|attr| attr.path().is_ident("action"))
        .map(get_attribute)
        .map(resolve_path)
        .collect();

    let manifest = manifests.into_iter().next().expect("a path to an action manifest (action.yml) file needs to be provided with the #[action = \"PATH\"] attribute");
    (name, generics, manifest)
}

#[proc_macro_derive(Action, attributes(action))]
pub fn action_derive(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    let ast: syn::DeriveInput = syn::parse2(input.into()).unwrap();
    let (struct_name, generics, manifest_path) = parse_derive(&ast);
    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();

    let manifest = Manifest::from_action_yml(manifest_path);
    // dbg!(&manifest);

    let input_enum_variants: Vec<_> = manifest
        .inputs
        .keys()
        .map(|name| {
            let variant = ident::str_to_enum_variant(name);
            quote! { #variant }
        })
        .collect();

    let input_enum_matches: Vec<_> = manifest
        .inputs
        .keys()
        .map(|name| {
            let variant = ident::str_to_enum_variant(name);
            quote! { #name => Ok(Self::#variant) }
        })
        .collect();

    let input_enum_ident = quote::format_ident!("{}Input", struct_name);
    let input_enum = quote! {
        #[derive(Debug, Hash, PartialEq, Eq, Clone, Copy)]
        pub enum #input_enum_ident {
            #(#input_enum_variants,)*
        }

        impl std::str::FromStr for #input_enum_ident {
            type Err = ();
            fn from_str(input: &str) -> Result<Self, Self::Err> {
                match input {
                    #(#input_enum_matches,)*
                    _  => Err(()),
                }
            }
        }
    };
    // eprintln!("{}", pretty_print(&quote! { #input_enum }));

    let parse_impl = quote! {
        #[allow(clippy::all)]
        impl #impl_generics ::action_core::Parse for #struct_name #ty_generics #where_clause {
            type Input = #input_enum_ident;

            fn parse_from<E: ::action_core::env::Read>(env: &E) -> std::collections::HashMap<Self::Input, Option<String>> {
                Self::inputs().iter().filter_map(|(name, input)| {
                    let value = ::action_core::input::ParseInput::parse_input::<String>(env, name);
                    let default = input.default.map(|s| s.to_string());
                    match std::str::FromStr::from_str(&name) {
                        Ok(variant) => Some((variant, value.unwrap().or(default))),
                        Err(_) => None,
                    }
                }).collect()
            }
        }
    };

    let input_impl_methods = input_impl_methods(&manifest);
    let input_impl = quote! {
        #[allow(clippy::all)]
        impl #impl_generics #struct_name #ty_generics #where_clause {
            #input_impl_methods
        }
    };

    let tokens = quote! {
        #input_enum
        #input_impl
        #parse_impl
    };
    // eprintln!("{}", pretty_print(&tokens));
    tokens.into()
}

fn input_impl_methods(manifest: &Manifest) -> TokenStream {
    let Manifest {
        name,
        description,
        author,
        ..
    } = manifest;

    let derived_methods: TokenStream = manifest
        .inputs
        .keys()
        .map(|name| {
            let fn_name = ident::parse_str(name);
            quote! {
                pub fn #fn_name<T>() -> Result<Option<T>, <T as ::action_core::input::Parse>::Error>
                where T: ::action_core::input::Parse {
                    let env = ::action_core::env::OsEnv::default();
                    ::action_core::input::ParseInput::parse_input::<T>(&env, #name)
                }
            }
        })
        .collect();

    let inputs: Vec<_> = manifest
        .inputs
        .iter()
        .map(|(name, input)| {
            let description = quote_option(input.description.as_ref());
            let deprecation_message = quote_option(input.deprecation_message.as_ref());
            let r#default = quote_option(input.default.as_ref());
            let required = quote_option(input.required.as_ref());
            quote! {
                (#name, ::action_core::input::Input {
                    description: #description,
                    deprecation_message: #deprecation_message,
                    default: #r#default,
                    required: #required,
                })
            }
        })
        .collect();
    // eprintln!("{}", pretty_print(&quote! { vec![#(#inputs,)*]; }));

    quote! {
        /// Inputs of this action.
        pub fn inputs() -> ::std::collections::HashMap<
            &'static str, ::action_core::input::Input<'static>
        > {
            static inputs: &'static [(&'static str, ::action_core::input::Input<'static>)] = &[
                #(#inputs,)*
            ];
            inputs.iter().cloned().collect()
        }

        /// Description of this action.
        pub fn description() -> &'static str {
            #description
        }

        /// Name of this action.
        pub fn name() -> &'static str {
            #name
        }

        /// Author of this trait.
        pub fn author() -> &'static str {
            #author
        }

        #derived_methods
    }
}

#[allow(dead_code)]
fn pretty_print(tokens: &TokenStream) -> String {
    let _file = syn::parse_file(&tokens.to_string()).unwrap();
    // TODO: this will not work until prettyplease updates to syn 2+
    // prettyplease::unparse(&file);
    tokens.to_string()
}