introduce enum for endianness

impl/src/bitfield/config.rs

@@ -4,9 +4,12 @@ use super::field_config::FieldConfig;
 use crate::errors::CombineError;
 use core::any::TypeId;
 use proc_macro2::Span;
-use std::collections::{
-    hash_map::Entry,
-    HashMap,
+use std::{
+    collections::{
+        hash_map::Entry,
+        HashMap,
+    },
+    convert::TryFrom, fmt,
 };
 use syn::parse::Result;
 
@@ -16,6 +19,7 @@ pub struct Config {
     pub bytes: Option<ConfigValue<usize>>,
     pub bits: Option<ConfigValue<usize>>,
     pub filled: Option<ConfigValue<bool>>,
+    pub endian: Option<ConfigValue<Endian>>,
     pub repr: Option<ConfigValue<ReprKind>>,
     pub derive_debug: Option<ConfigValue<()>>,
     pub derive_specifier: Option<ConfigValue<()>>,
@@ -57,6 +61,42 @@ impl core::fmt::Debug for ReprKind {
     }
 }
 
+/// Types of endiannes for a `#[bitfield]` struct.
+#[derive(Debug, Copy, Clone)]
+pub enum Endian {
+    Little,
+    Big,
+    Native,
+}
+
+impl TryFrom<String> for Endian {
+    type Error = ::syn::Error;
+
+    fn try_from(value: String) -> std::result::Result<Self, Self::Error> {
+        match value.as_str() {
+            "big" => Ok(Endian::Big),
+            "little" => Ok(Endian::Little),
+            "native" => Ok(Endian::Native),
+            invalid => {
+                Err(format_err!(
+                invalid,
+                "encountered invalid value argument for #[bitfield] `endian` parameter",
+                ))
+            }
+        }
+    }
+}
+
+impl fmt::Display for Endian {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", match self {
+            Endian::Big => "big",
+            Endian::Little => "little",
+            Endian::Native => "native"
+        })
+    }
+}
+
 /// A configuration value and its originating span.
 #[derive(Clone)]
 pub struct ConfigValue<T> {
@@ -234,6 +274,21 @@ impl Config {
         Ok(())
     }
 
+    /// Sets the `endian: str` #[bitfield] parameter to the given value.
+    ///
+    /// # Errors
+    ///
+    /// If the specifier has already been set.
+    pub fn endian(&mut self, value: Endian, span: Span) -> Result<()> {
+        match &self.endian {
+            Some(previous) => {
+                return Err(Self::raise_duplicate_error("endian", span, previous))
+            }
+            None => self.endian = Some(ConfigValue::new(value, span)),
+        }
+        Ok(())
+    }
+
     /// Registers the `#[repr(uN)]` attribute for the #[bitfield] macro.
     ///
     /// # Errors

impl/src/bitfield/mod.rs

@@ -16,6 +16,8 @@ use syn::{
     parse::Result,
 };
 
+pub use config::Endian;
+
 /// Analyzes the given token stream for `#[bitfield]` properties and expands code if valid.
 pub fn analyse_and_expand(args: TokenStream2, input: TokenStream2) -> TokenStream2 {
     match analyse_and_expand_or_error(args, input) {

impl/src/bitfield/params.rs

@@ -1,3 +1,5 @@
+use std::convert::TryInto;
+
 use super::config::Config;
 use proc_macro2::Span;
 use syn::{
@@ -112,6 +114,28 @@ impl Config {
         Ok(())
     }
 
+    /// Feeds am `endian: string` parameter to the `#[bitfield]` configuration.
+    fn feed_endian_param(&mut self, name_value: syn::MetaNameValue) -> Result<()> {
+        assert!(name_value.path.is_ident("endian"));
+        match &name_value.lit {
+            syn::Lit::Str(lit_str) => {
+                let endian = match lit_str.value().try_into() {
+                    Ok(endian) => endian,
+                    Err(err) => return Err(err),
+                };
+
+                self.endian(endian, name_value.span())?;
+            }
+            invalid => {
+                return Err(format_err!(
+                invalid,
+                "encountered invalid value argument for #[bitfield] `endian` parameter",
+            ))
+            }
+        }
+        Ok(())
+    }
+
     /// Feeds the given parameters to the `#[bitfield]` configuration.
     ///
     /// # Errors
@@ -132,6 +156,8 @@ impl Config {
                                 self.feed_bits_param(name_value)?;
                             } else if name_value.path.is_ident("filled") {
                                 self.feed_filled_param(name_value)?;
+                            } else if name_value.path.is_ident("endian") {
+                                self.feed_endian_param(name_value)?;
                             } else {
                                 return Err(unsupported_argument(name_value))
                             }

impl/src/bitfield_specifier.rs

@@ -1,6 +1,9 @@
+use std::convert::TryInto;
+
 use proc_macro2::TokenStream as TokenStream2;
-use quote::quote_spanned;
+use quote::{quote, quote_spanned};
 use syn::spanned::Spanned as _;
+use crate::bitfield::Endian;
 
 pub fn generate(input: TokenStream2) -> TokenStream2 {
     match generate_or_error(input) {
@@ -39,7 +42,7 @@ fn generate_or_error(input: TokenStream2) -> syn::Result<TokenStream2> {
 }
 struct Attributes {
     bits: Option<usize>,
-    endian: Option<usize>, // TODO switch to enum
+    endian: Option<Endian>,
 }
 
 fn parse_attrs(attrs: &[syn::Attribute]) -> syn::Result<Attributes> {
@@ -80,9 +83,9 @@ fn parse_attrs(attrs: &[syn::Attribute]) -> syn::Result<Attributes> {
             let meta = attr.parse_meta()?;
             attributes.endian = match meta {
                 syn::Meta::NameValue(syn::MetaNameValue {
-                    lit: syn::Lit::Int(lit),
+                    lit: syn::Lit::Str(lit),
                     ..
-                }) => Some(lit.base10_parse::<usize>()?),
+                }) => Some(lit.value().try_into()?),
                 _ => {
                     return Err(format_err_spanned!(
                         attr,
@@ -126,8 +129,8 @@ fn generate_enum(input: syn::ItemEnum) -> syn::Result<TokenStream2> {
     };
 
     let endian = match attributes.endian {
-        Some(endian) => endian, // 1 big, 2 little
-        None => 0, // Default to host endian
+        Some(endian) => endian,
+        None => Endian::Native // Default to host endian
     };
 
     println!("{} endian {}", enum_ident, endian);
@@ -160,6 +163,19 @@ fn generate_enum(input: syn::ItemEnum) -> syn::Result<TokenStream2> {
         )
     });
 
+    let endian_to = match endian {
+        Endian::Big => quote!{ (input as Self::Bytes).to_be() },
+        Endian::Little => quote!{ (input as Self::Bytes).to_le() },
+        _ => quote!{ (input as Self::Bytes)},
+    };
+
+
+    let endian_from = match endian {
+        Endian::Big => quote!{ Self::Bytes::from_be() },
+        Endian::Little => quote!{ Self::Bytes::from_le() },
+        _ => quote!{ bytes },
+    };
+
     Ok(quote_spanned!(span=>
         #( #check_discriminants )*
 
@@ -170,21 +186,13 @@ fn generate_enum(input: syn::ItemEnum) -> syn::Result<TokenStream2> {
 
             #[inline]
             fn into_bytes(input: Self::InOut) -> ::core::result::Result<Self::Bytes, ::modular_bitfield::error::OutOfBounds> {
-                let bytes = match #endian {
-                    1 => (input as Self::Bytes).to_be(),
-                    2 => (input as Self::Bytes).to_le(),
-                    _ => input as Self::Bytes,
-                };
+                let bytes = #endian_to;
                 return ::core::result::Result::Ok(bytes);
             }
 
             #[inline]
             fn from_bytes(bytes: Self::Bytes) -> ::core::result::Result<Self::InOut, ::modular_bitfield::error::InvalidBitPattern<Self::Bytes>> {
-                let bytes = match #endian {
-                    1 => Self::Bytes::from_be(bytes),
-                    2 => Self::Bytes::from_le(bytes),
-                    _ => bytes,
-                };
+                let bytes = #endian_from;
 
                 match bytes {
                     #( #from_bytes_arms ),*