Function parse_rename_attrs

structmap-derive/src/lib.rs:174–226

Helper method used to parse out any `rename` attribute definitions in a struct marked with the ToMap trait, returning a mapping between the original field name and the one being changed for later use when doing codegen.

(fields: &Fields)

/// marked with the ToMap trait, returning a mapping between the original field name
/// and the one being changed for later use when doing codegen.
fn parse_rename_attrs(fields: &Fields) -> BTreeMap<String, String> {
    let mut rename: BTreeMap<String, String> = BTreeMap::new();

    // != for if let not yet introduced
    if let Fields::Named(_) = fields {
        // no-op
    } else {
        panic!("Must have named fields.");
    }

    // iterate over fields available and attributes
    for field in fields.iter() {
        for attr in field.attrs.iter() {
            // parse original struct field name
            let field_name = field.ident.as_ref().unwrap().to_string();
            if rename.contains_key(&field_name) {
                panic!("Cannot redefine field name multiple times.");
            }

            // parse out name value pairs in attributes
            // first get `lst` in #[rename(lst)]
            match attr.parse_meta() {
                Ok(syn::Meta::List(lst)) => {
                    // then parse key-value name
                    match lst.nested.first() {
                        Some(syn::NestedMeta::Meta(syn::Meta::NameValue(nm))) => {
                            // check path to be = `name`
                            let path = nm.path.get_ident().unwrap().to_string();
                            if path != "name" {
                                panic!("{}", RENAME_ERROR_MSG);
                            }

                            let lit = match &nm.lit {
                                syn::Lit::Str(val) => val.value(),
                                _ => {
                                    panic!("{}", RENAME_ERROR_MSG);
                                }
                            };
                            rename.insert(field_name, lit);
                        }
                        _ => {
                            panic!("{}", RENAME_ERROR_MSG);
                        }
                    }
                }
                _ => {
                    panic!("{}", RENAME_ERROR_MSG);
                }
            }
        }
    }
    rename
}