Resolve issue #406 for structures

src/macros/seq.rs

@@ -22,7 +22,10 @@
 /// // Parse into structs / tuple-structs
 /// fn field(input: &mut &[u8]) -> PResult<Field> {
 ///     seq!{Field {
-///         namespace: empty.value(5),
+///         // `#[temp]` fields can be referenced later
+///         // but they are ignored when building the struct
+///         #[temp] ten: empty.value(10),
+///         namespace: empty.value(ten / 2),
 ///         name: alphanumeric1.map(|s: &[u8]| s.to_owned()),
 ///         // `_` fields are ignored when building the struct
 ///         _: (space0, b':', space0),
@@ -119,13 +122,14 @@ macro_rules! seq_parse_struct_fields {
     };
     (
         $input: ident;
-        $head_field: ident : $head_parser: expr, $($fields: tt)*
+        $(#[temp])? $head_field: ident : $head_parser: expr, $($fields: tt)*
     ) => {
         let $head_field = $head_parser.parse_next($input)?;
         $crate::seq_parse_struct_fields!($input; $($fields)*)
     };
     (
         $input: ident;
+        // `#[temp]` in the last field makes no sense
         $head_field: ident : $head_parser: expr
     ) => {
         let $head_field = $head_parser.parse_next($input)?;
@@ -192,6 +196,14 @@ macro_rules! seq_init_struct_fields {
     ) => {
         $crate::seq_init_struct_fields!( (); $name ; $($inits)* )
     };
+    (
+        (#[temp] $head_field: ident : $head_parser: expr, $($fields: tt)*);
+        $name: ident;
+        $($inits: tt)*
+    ) =>
+    {
+        $crate::seq_init_struct_fields!( ( $($fields)* ) ; $name ; $($inits)* )
+    };
     (
         ($head_field: ident : $head_parser: expr, $($fields: tt)*);
         $name: ident;

src/macros/test.rs

@@ -119,6 +119,46 @@ fn seq_struct_default_init() {
     );
 }
 
+#[test]
+fn seq_struct_referring_elided() {
+    #[derive(Debug, PartialEq, Default)]
+    struct Point {
+        x: u32,
+        y: u32,
+    }
+
+    fn parser(input: &mut &str) -> PResult<Point> {
+        seq! {
+            Point {
+                #[temp] half_x: dec_uint::<_, u32, _>,
+                x: empty.value(half_x * 2),
+                _: ',',
+                #[temp] half_y: dec_uint::<_, u32, _>,
+                y: empty.value(half_y * 2),
+            }
+        }
+        .parse_next(input)
+    }
+    assert_eq!(
+        parser.parse_peek("123,4 remaining"),
+        Ok((" remaining", Point { x: 246, y: 8 },)),
+    );
+    assert_eq!(
+        parser.parse_peek("123, remaining"),
+        Err(ErrMode::Backtrack(ParserError::from_error_kind(
+            &" remaining",
+            ErrorKind::Fail
+        )))
+    );
+    assert_eq!(
+        parser.parse_peek(""),
+        Err(ErrMode::Backtrack(ParserError::from_error_kind(
+            &"",
+            ErrorKind::Fail
+        )))
+    );
+}
+
 #[test]
 fn seq_struct_trailing_comma_elided() {
     #![allow(dead_code)]