Add #[align] attribute to structs

This attribute aligns the reader to byte boundary

It can be applied to enums & structs to align before reading any fields or the discriminant

It can also be applied to individual struct fields to align the reader before reading the field

Finally, you can apply it to non-unit enum variants to align the reader after reading the discriminant, but before reading the payload

bitbuffer_derive/tests/read.rs

@@ -335,3 +335,79 @@ fn test_bit_size_sized() {
         Some(8 + 8 * 16 + 1)
     );
 }
+
+#[derive(BitRead, PartialEq, Debug)]
+#[align]
+struct AlignStruct(u8);
+
+#[test]
+fn test_align() {
+    let bytes = vec![0, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
+    let buffer = BitReadBuffer::new(&bytes, BigEndian);
+    let mut stream = BitReadStream::from(buffer);
+    stream.read_bool().unwrap();
+    assert_eq!(AlignStruct(0x80), stream.read().unwrap());
+    assert_eq!(16, stream.pos());
+    assert_eq!(None, bit_size_of::<AlignStruct>());
+}
+
+#[derive(BitRead, PartialEq, Debug)]
+#[align]
+struct AlignFieldStruct {
+    #[size = 1]
+    foo: u8,
+    #[align]
+    bar: u8,
+}
+
+#[test]
+fn test_align_field() {
+    let bytes = vec![0, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
+    let buffer = BitReadBuffer::new(&bytes, BigEndian);
+    let mut stream = BitReadStream::from(buffer);
+    assert_eq!(
+        AlignFieldStruct { foo: 0, bar: 0x80 },
+        stream.read().unwrap()
+    );
+    assert_eq!(16, stream.pos());
+    assert_eq!(None, bit_size_of::<AlignStruct>());
+}
+
+#[derive(BitRead, PartialEq, Debug)]
+#[discriminant_bits = 4]
+#[align]
+enum AlignEnum {
+    Foo,
+    Bar(u8),
+}
+
+#[test]
+fn test_align_enum() {
+    let bytes = vec![0x00, 0x18, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
+    let buffer = BitReadBuffer::new(&bytes, BigEndian);
+    let mut stream = BitReadStream::from(buffer);
+    stream.read_bool().unwrap();
+    assert_eq!(AlignEnum::Bar(0x80), stream.read().unwrap());
+    assert_eq!(20, stream.pos());
+    assert_eq!(None, bit_size_of::<AlignEnum>());
+}
+
+#[derive(BitRead, PartialEq, Debug)]
+#[discriminant_bits = 4]
+#[align]
+enum AlignEnumField {
+    Foo,
+    #[align]
+    Bar(u8),
+}
+
+#[test]
+fn test_align_enum_field() {
+    let bytes = vec![0x00, 0x10, 0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0];
+    let buffer = BitReadBuffer::new(&bytes, BigEndian);
+    let mut stream = BitReadStream::from(buffer);
+    stream.read_bool().unwrap();
+    assert_eq!(AlignEnumField::Bar(0x80), stream.read().unwrap());
+    assert_eq!(24, stream.pos());
+    assert_eq!(None, bit_size_of::<AlignEnum>());
+}