Restore last bit read during id_pat

* Restore last leftover reading in reader for bit reads during ip_pat

Author: wcampbell0x2a

deku-derive/src/macros/deku_read.rs

@@ -371,6 +371,7 @@ fn emit_enum(input: &DekuData) -> Result<TokenStream, syn::Error> {
 
     let variant_read = quote! {
         __deku_reader.last_bits_read_amt = 0;
+        let __deku_last_leftover = __deku_reader.leftover.clone();
         #variant_id_read
 
         #(#pre_match_tokens)*
@@ -822,6 +823,7 @@ fn emit_field_read(
                     if let Err(e) = __deku_reader.seek_last_read() {
                         return Err(::#crate_::DekuError::Io(e.kind()));
                     }
+                    __deku_reader.leftover = __deku_last_leftover;
                     #type_as_deku_read::from_reader_with_ctx
                     (
                         __deku_reader,

src/reader.rs

@@ -21,8 +21,9 @@ pub enum ReaderRet {
     Bits(Option<BitVec<u8, Msb0>>),
 }
 
-#[derive(Debug)]
-enum Leftover {
+/// Bits or Byte stored from previous read, such as the case of id_pat
+#[derive(Debug, Clone)]
+pub enum Leftover {
     Byte(u8),
     #[cfg(feature = "bits")]
     Bits(BitVec<u8, Msb0>),
@@ -32,7 +33,7 @@ enum Leftover {
 pub struct Reader<'a, R: Read + Seek> {
     inner: &'a mut R,
     /// bits stored from previous reads that didn't read to the end of a byte size
-    leftover: Option<Leftover>,
+    pub leftover: Option<Leftover>,
     /// Amount of bits read after last read, reseted before reading enum ids
     pub last_bits_read_amt: usize,
     /// Amount of bits read during the use of [read_bits](Reader::read_bits) and [read_bytes](Reader::read_bytes)
@@ -75,6 +76,8 @@ impl<'a, R: Read + Seek> Reader<'a, R> {
     pub fn seek_last_read(&mut self) -> no_std_io::io::Result<()> {
         let number = self.last_bits_read_amt as i64;
         let seek_amt = (number / 8).saturating_add((number % 8).signum());
+        #[cfg(feature = "logging")]
+        log::trace!("seek_last_read: {seek_amt:?}");
         self.seek(SeekFrom::Current(seek_amt.saturating_neg()))?;
         self.bits_read -= self.last_bits_read_amt;
         self.leftover = None;

tests/test_regression.rs

@@ -385,3 +385,23 @@ fn issue_397() {
     }
     let _ = Packet::from_bytes((&[0x00, 0x01], 0));
 }
+
+#[test]
+fn issue_533() {
+    #[derive(PartialEq, Debug, DekuRead)]
+    #[deku(id_type = "u8", bits = "1")]
+    pub enum BitsAndValue {
+        #[deku(id = 0)]
+        Zero,
+        #[deku(id_pat = "_")]
+        Other(#[deku(bits = 1)] u8),
+    }
+    let input = [0b0100_0000];
+    let mut cursor = Cursor::new(input);
+    let mut reader = Reader::new(&mut cursor);
+    let v = BitsAndValue::from_reader_with_ctx(&mut reader, ()).unwrap();
+    assert_eq!(v, BitsAndValue::Zero);
+
+    let v = BitsAndValue::from_reader_with_ctx(&mut reader, ()).unwrap();
+    assert_eq!(v, BitsAndValue::Other(1));
+}