syn-helpers 0.5.0

Framework for building derive macros
Documentation 
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use std::collections::HashMap;
use syn::{self, visit::Visit, visit_mut::VisitMut, Ident, PathArguments, TypeParam};

/// Renames types from a map
pub(crate) struct RenameGenerics<'a>(pub &'a HashMap<Ident, Ident>);

impl<'a> VisitMut for RenameGenerics<'a> {
    fn visit_type_reference_mut(&mut self, i: &mut syn::TypeReference) {
        if let Some(ref mut lifetime) = i.lifetime {
            if let Some(rewrite) = self.0.get(&lifetime.ident).cloned() {
                lifetime.ident = rewrite;
            }
        }
        self.visit_type_mut(&mut i.elem);
    }

    fn visit_type_path_mut(&mut self, i: &mut syn::TypePath) {
        if let Some(current_ident) = i.path.get_ident() {
            if let Some(rewrite) = self.0.get(current_ident).cloned() {
                i.path = rewrite.into();
            }
        }
    }
}

/// Finds types which reference a type which is generic
pub(crate) struct ReferencesAGeneric<'a> {
    pub(crate) found: bool,
    pub(crate) generics_on_structures: &'a syn::Generics,
}

impl<'a> ReferencesAGeneric<'a> {
    pub(crate) fn has_generic(ty: &syn::Type, generics_on_structures: &'a syn::Generics) -> bool {
        let mut state = ReferencesAGeneric {
            found: false,
            generics_on_structures,
        };
        state.visit_type(ty);
        state.found
    }

    fn get_just_type_generics(&self) -> impl Iterator<Item = &TypeParam> {
        self.generics_on_structures
            .params
            .iter()
            .filter_map(|param| {
                if let syn::GenericParam::Type(ty) = param {
                    Some(ty)
                } else {
                    None
                }
            })
    }
}

impl<'a, 'b> Visit<'b> for ReferencesAGeneric<'a> {
    fn visit_type_path(&mut self, i: &'b syn::TypePath) {
        if self.found {
            return;
        }

        if let Some(segment) = i.path.segments.first() {
            if let PathArguments::AngleBracketed(ref arguments) = segment.arguments {
                self.visit_angle_bracketed_generic_arguments(arguments);
            }

            let found = self
                .get_just_type_generics()
                .any(|ty| ty.ident == segment.ident);

            self.found |= found;
        } else {
            panic!("path segments empty ??");
        }
    }
}