datalit-macros-internals 0.1.0-alpha.4

Internals for the datalit crate
Documentation 
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//! Basic parsing structures.
//!
//! These can be used as members of other structures to build up more complex parsing.

use proc_macro2::TokenStream;
use syn::{Ident, parse::ParseStream};

use crate::to_bytes::{Endianness, IntType};

#[derive(Debug, Clone)]
pub struct PrimitiveSpec {
    ident: Ident,
    int_type: IntType,
    endianness: Option<Endianness>,
}

impl PrimitiveSpec {
    pub fn int_type(&self) -> IntType {
        self.int_type
    }

    pub fn write_int(
        &self,
        default_endianness: Endianness,
        n: &num::BigInt,
        buffer: &mut [u8],
    ) -> syn::Result<()> {
        let int_type = self.int_type();
        let endianness = self.endianness.unwrap_or(default_endianness);
        int_type.write_bytes_from_bigint(n, endianness, buffer)
    }
}

impl syn::parse::Parse for PrimitiveSpec {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        let ident: Ident = input.parse()?;
        let ident_string = ident.to_string();
        let mut suffix = ident_string.as_str();

        let endianness = Endianness::parse_from_suffix(&mut suffix);

        let int_type = IntType::from_suffix(suffix).ok_or_else(|| {
            syn::Error::new_spanned(
                &ident,
                format!("Invalid or missing integer type suffix: '{}'", ident),
            )
        })?;

        Ok(PrimitiveSpec {
            ident,
            int_type,
            endianness,
        })
    }
}

impl quote::ToTokens for PrimitiveSpec {
    fn to_tokens(&self, tokens: &mut TokenStream) {
        self.ident.to_tokens(tokens);
    }
}