Implement nom::sequence::Tuple for () (Unit)

src/sequence/mod.rs

@@ -252,6 +252,15 @@ macro_rules! tuple_trait_inner(
 tuple_trait!(FnA A, FnB B, FnC C, FnD D, FnE E, FnF F, FnG G, FnH H, FnI I, FnJ J, FnK K, FnL L,
   FnM M, FnN N, FnO O, FnP P, FnQ Q, FnR R, FnS S, FnT T, FnU U);
 
+// Special case: implement `Tuple` for `()`, the unit type.
+// This can come up in macros which accept a variable number of arguments.
+// Literally, `()` is an empty tuple, so it should simply parse nothing.
+impl<I, E: ParseError<I>> Tuple<I, (), E> for () {
+  fn parse(&mut self, input: I) -> IResult<I, (), E> {
+    Ok((input, ()))
+  }
+}
+
 ///Applies a tuple of parsers one by one and returns their results as a tuple.
 ///There is a maximum of 21 parsers
 /// ```rust

src/sequence/tests.rs

@@ -1,6 +1,6 @@
 use super::*;
 use crate::bytes::streaming::{tag, take};
-use crate::error::ErrorKind;
+use crate::error::{ErrorKind, Error};
 use crate::internal::{Err, IResult, Needed};
 use crate::number::streaming::be_u16;
 
@@ -272,3 +272,10 @@ fn tuple_test() {
     Err(Err::Error(error_position!(&b"jk"[..], ErrorKind::Tag)))
   );
 }
+
+#[test]
+fn unit_type() {
+  assert_eq!(tuple::<&'static str, (), Error<&'static str>, ()>(())("abxsbsh"), Ok(("abxsbsh", ())));
+  assert_eq!(tuple::<&'static str, (), Error<&'static str>, ()>(())("sdfjakdsas"), Ok(("sdfjakdsas", ())));
+  assert_eq!(tuple::<&'static str, (), Error<&'static str>, ()>(())(""), Ok(("", ())));
+}