schemars/schemars_derive/src/preprocess.rs

use quote::ToTokens;
use serde_derive_internals::Ctxt;
use std::collections::BTreeSet;
use syn::parse::Parser;
use syn::{Attribute, Data, DeriveInput, Field, GenericParam, Generics, Meta, NestedMeta, Variant};

// List of keywords that can appear in #[serde(...)]/#[schemars(...)] attributes, which we want serde to parse for us.
static SERDE_KEYWORDS: &[&str] = &[
    "rename",
    "rename_all",
    "deny_unknown_fields",
    "tag",
    "content",
    "untagged",
    "bound",
    "default",
    "remote",
    "alias",
    "skip",
    "skip_serializing",
    "skip_serializing_if",
    "skip_deserializing",
    "other",
    "flatten",
    // special cases - these keywords are not copied from schemars attrs to serde attrs
    "serialize_with",
    "deserialize_with",
    "with",
];

pub fn add_trait_bounds(generics: &mut Generics) {
    for param in &mut generics.params {
        if let GenericParam::Type(ref mut type_param) = *param {
            type_param.bounds.push(parse_quote!(schemars::JsonSchema));
        }
    }
}

// If a struct/variant/field has any #[schemars] attributes, then rename them
// to #[serde] so that serde_derive_internals will parse them for us.
pub fn process_serde_attrs(input: &mut DeriveInput) -> Result<(), Vec<syn::Error>> {
    let ctxt = Ctxt::new();
    process_attrs(&ctxt, &mut input.attrs);
    match input.data {
        Data::Struct(ref mut s) => process_serde_field_attrs(&ctxt, s.fields.iter_mut()),
        Data::Enum(ref mut e) => process_serde_variant_attrs(&ctxt, e.variants.iter_mut()),
        Data::Union(ref mut u) => process_serde_field_attrs(&ctxt, u.fields.named.iter_mut()),
    };

    ctxt.check()
}

fn process_serde_variant_attrs<'a>(ctxt: &Ctxt, variants: impl Iterator<Item = &'a mut Variant>) {
    for v in variants {
        process_attrs(&ctxt, &mut v.attrs);
        process_serde_field_attrs(&ctxt, v.fields.iter_mut());
    }
}

fn process_serde_field_attrs<'a>(ctxt: &Ctxt, fields: impl Iterator<Item = &'a mut Field>) {
    for f in fields {
        process_attrs(&ctxt, &mut f.attrs);
    }
}

fn process_attrs(ctxt: &Ctxt, attrs: &mut Vec<Attribute>) {
    let (serde_attrs, other_attrs): (Vec<_>, Vec<_>) =
        attrs.drain(..).partition(|at| at.path.is_ident("serde"));

    *attrs = other_attrs;

    let schemars_attrs: Vec<_> = attrs
        .iter()
        .filter(|at| at.path.is_ident("schemars"))
        .collect();

    let (mut serde_meta, mut schemars_meta_names): (Vec<_>, BTreeSet<_>) = schemars_attrs
        .iter()
        .flat_map(|at| get_meta_items(&ctxt, at))
        .flatten()
        .filter_map(|meta| {
            let keyword = get_meta_ident(&ctxt, &meta).ok()?;
            if keyword.ends_with("with") || !SERDE_KEYWORDS.contains(&keyword.as_ref()) {
                None
            } else {
                Some((meta, keyword))
            }
        })
        .unzip();

    if schemars_meta_names.contains("skip") {
        schemars_meta_names.insert("skip_serializing".to_string());
        schemars_meta_names.insert("skip_deserializing".to_string());
    }

    for meta in serde_attrs
        .into_iter()
        .flat_map(|at| get_meta_items(&ctxt, &at))
        .flatten()
    {
        if let Ok(i) = get_meta_ident(&ctxt, &meta) {
            if !schemars_meta_names.contains(&i) && SERDE_KEYWORDS.contains(&i.as_ref()) {
                serde_meta.push(meta);
            }
        }
    }

    if !serde_meta.is_empty() {
        let new_serde_attr = quote! {
            #[serde(#(#serde_meta),*)]
        };

        let parser = Attribute::parse_outer;
        match parser.parse2(new_serde_attr) {
            Ok(ref mut parsed) => attrs.append(parsed),
            Err(e) => ctxt.error_spanned_by(to_tokens(attrs), e),
        }
    }
}

fn to_tokens(attrs: &[Attribute]) -> impl ToTokens {
    let mut tokens = proc_macro2::TokenStream::new();
    for attr in attrs {
        attr.to_tokens(&mut tokens);
    }
    tokens
}

fn get_meta_items(ctxt: &Ctxt, attr: &Attribute) -> Result<Vec<NestedMeta>, ()> {
    match attr.parse_meta() {
        Ok(Meta::List(meta)) => Ok(meta.nested.into_iter().collect()),
        Ok(_) => {
            ctxt.error_spanned_by(attr, "expected #[schemars(...)] or #[serde(...)]");
            Err(())
        }
        Err(err) => {
            ctxt.error_spanned_by(attr, err);
            Err(())
        }
    }
}

fn get_meta_ident(ctxt: &Ctxt, meta: &NestedMeta) -> Result<String, ()> {
    match meta {
        NestedMeta::Meta(m) => m.path().get_ident().map(|i| i.to_string()).ok_or(()),
        NestedMeta::Lit(lit) => {
            ctxt.error_spanned_by(
                meta,
                format!(
                    "unexpected literal in attribute: {}",
                    lit.into_token_stream()
                ),
            );
            Err(())
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use pretty_assertions::assert_eq;
    use syn::DeriveInput;

    #[test]
    fn test_process_serde_attrs() {
        let mut input: DeriveInput = parse_quote! {
            #[serde(rename(serialize = "ser_name"), rename_all = "camelCase")]
            #[serde(default, unknown_word)]
            #[schemars(rename = "overriden", another_unknown_word)]
            #[misc]
            struct MyStruct {
                /// blah blah blah
                #[serde(alias = "first")]
                field1: i32,
                #[serde(serialize_with = "se", deserialize_with = "de")]
                #[schemars(with = "with")]
                field2: i32,
                #[schemars(skip)]
                #[serde(skip_serializing)]
                field3: i32,
            }
        };
        let expected: DeriveInput = parse_quote! {
            #[schemars(rename = "overriden", another_unknown_word)]
            #[misc]
            #[serde(rename = "overriden", rename_all = "camelCase", default)]
            struct MyStruct {
                #[doc = r" blah blah blah"]
                #[serde(alias = "first")]
                field1: i32,
                #[schemars(with = "with")]
                #[serde(serialize_with = "se", deserialize_with = "de")]
                field2: i32,
                #[schemars(skip)]
                #[serde(skip)]
                field3: i32,
            }
        };

        if let Err(e) = process_serde_attrs(&mut input) {
            panic!("process_serde_attrs returned error: {}", e[0])
        };

        assert_eq!(input, expected);
    }
}