educe 0.7.4

This crate offers procedural macros designed to facilitate the swift implementation of Rust's built-in traits.
Documentation 
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use std::collections::BTreeMap;

use syn::{Attribute, Meta, Path, Token, punctuated::Punctuated};

use crate::{
    Trait,
    common::{path::meta_2_path, tools::HashType, r#type::TypeWithPunctuatedMeta},
    panic,
};

/// The parsed settings of a field-level `Into` attribute.
pub(crate) struct FieldAttribute {
    pub(crate) types: BTreeMap<HashType, Option<Path>>,
}

#[derive(Debug)]
/// Parses field-level `Into` metas; the `enable_*` switches describe which parameters are allowed for the current shape of data.
pub(crate) struct FieldAttributeBuilder {
    pub(crate) enable_types: bool,
}

impl FieldAttributeBuilder {
    /// Parses one field-level `Into` meta into a `FieldAttribute`, rejecting parameters that are not enabled here.
    pub(crate) fn build_from_into_meta(&self, meta: &[Meta]) -> syn::Result<FieldAttribute> {
        debug_assert!(!meta.is_empty());

        let mut types = BTreeMap::new();

        for meta in meta {
            debug_assert!(meta.path().is_ident("Into"));

            let correct_usage_for_into_attribute = {
                let mut usage = vec![];

                if self.enable_types {
                    usage.push(stringify!(#[educe(Into(type))]));
                    usage.push(stringify!(#[educe(Into(type, method(path_to_method)))]));
                }

                usage
            };

            match meta {
                Meta::Path(_) | Meta::NameValue(_) => {
                    return Err(panic::attribute_incorrect_format(
                        meta.path().get_ident().unwrap(),
                        &correct_usage_for_into_attribute,
                    ));
                },
                Meta::List(list) => {
                    if !self.enable_types {
                        return Err(panic::attribute_incorrect_format(
                            meta.path().get_ident().unwrap(),
                            &correct_usage_for_into_attribute,
                        ));
                    }

                    let TypeWithPunctuatedMeta {
                        ty,
                        list: result,
                    } = list.parse_args()?;

                    let ty = super::super::common::to_hash_type(&ty);

                    let mut method = None;
                    let mut method_is_set = false;

                    let mut handler = |meta: Meta| -> syn::Result<bool> {
                        if let Some(ident) = meta.path().get_ident()
                            && ident == "method"
                        {
                            let v = meta_2_path(&meta)?;

                            if method_is_set {
                                return Err(panic::parameter_reset(ident));
                            }

                            method_is_set = true;

                            method = Some(v);

                            return Ok(true);
                        }

                        Ok(false)
                    };

                    for p in result {
                        if !handler(p)? {
                            return Err(panic::attribute_incorrect_format(
                                meta.path().get_ident().unwrap(),
                                &correct_usage_for_into_attribute,
                            ));
                        }
                    }

                    if types.contains_key(&ty) {
                        return Err(super::super::panic::reset_a_type(&ty));
                    }

                    types.insert(ty, method);
                },
            }
        }

        Ok(FieldAttribute {
            types,
        })
    }

    /// Scans the `#[educe(...)]` attributes of a field and parses its `Into` meta if present.
    pub(crate) fn build_from_attributes(
        &self,
        attributes: &[Attribute],
        traits: &[Trait],
    ) -> syn::Result<FieldAttribute> {
        let mut output: Option<FieldAttribute> = None;

        let mut v_meta = Vec::new();

        for attribute in attributes.iter() {
            let path = attribute.path();

            if path.is_ident("educe")
                && let Meta::List(list) = &attribute.meta
            {
                let result =
                    list.parse_args_with(Punctuated::<Meta, Token![,]>::parse_terminated)?;

                for meta in result {
                    let path = meta.path();

                    let t = match Trait::from_path(path) {
                        Some(t) => t,
                        None => return Err(panic::unsupported_trait(meta.path())),
                    };

                    if !traits.contains(&t) {
                        return Err(panic::trait_not_used(path.get_ident().unwrap()));
                    }

                    if t == Trait::Into {
                        v_meta.push(meta);
                    }
                }
            }
        }

        if !v_meta.is_empty() {
            output = Some(self.build_from_into_meta(&v_meta)?);
        }

        Ok(output.unwrap_or_else(|| FieldAttribute {
            types: BTreeMap::new()
        }))
    }
}