simplify Deserialize impl for Atoms

src/bng/score.rs

@@ -33,7 +33,7 @@ pub use de::*;
 
 use super::Expression as Instruction;
 
-#[derive(Deref, From)]
+#[derive(Deref, From, Default)]
 #[cfg_attr(debug_assertions, derive(Serialize, Debug))]
 pub struct Atoms(Vec<Atom>);
 

src/bng/score/de.rs

@@ -2,7 +2,7 @@ use derive_new::new;
 use nom::{
     character::complete::one_of,
     combinator::all_consuming,
-    multi::many0,
+    multi::{many0, many1},
     sequence::{preceded, terminated},
     Parser,
 };
@@ -60,56 +60,13 @@ impl<'de> Deserialize<'de> for Atoms {
             notes: String,
             sheet: String,
         }
-        struct NotesSheetVisitor;
-        impl<'de> Visitor<'de> for NotesSheetVisitor {
-            type Value = NotesSheet;
-            fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
-                formatter.write_str("a \"notes\" field and a \"sheet\" field")
-            }
-            fn visit_seq<A>(self, mut seq: A) -> Result<Self::Value, A::Error>
-            where
-                A: serde::de::SeqAccess<'de>,
-            {
-                let notes = seq
-                    .next_element()?
-                    .ok_or_else(|| de::Error::invalid_length(0, &self))?;
-                let sheet = seq
-                    .next_element()?
-                    .ok_or_else(|| de::Error::invalid_length(1, &self))?;
-                Ok(NotesSheet::new(notes, sheet))
-            }
-            fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error>
-            where
-                A: de::MapAccess<'de>,
-            {
-                let mut notes = None;
-                let mut sheet = None;
-                while let Some(key) = map.next_key()? {
-                    match key {
-                        Field::Notes => {
-                            if notes.is_some() {
-                                return Err(de::Error::duplicate_field("notes"));
-                            }
-                            notes = Some(map.next_value()?);
-                        }
-                        Field::Sheet => {
-                            if sheet.is_some() {
-                                return Err(de::Error::duplicate_field("sheet"));
-                            }
-                            sheet = Some(map.next_value()?);
-                        }
-                    }
-                }
-                let notes = notes.ok_or_else(|| de::Error::missing_field("notes"))?;
-                let sheet = sheet.ok_or_else(|| de::Error::missing_field("sheet"))?;
-                Ok(NotesSheet::new(notes, sheet))
-            }
-        }
-        const FIELDS: &[&str] = &["notes", "sheet"];
-        let NotesSheet { notes, sheet } =
-            deserializer.deserialize_struct("NotesSheet", FIELDS, NotesSheetVisitor)?;
+        let NotesSheet { notes, sheet } = NotesSheet::deserialize(deserializer)?;
+        if sheet.is_empty() {
+            Ok(Default::default())
+        } else {
             flat_atom_parser_mapper::<D, _>(&sheet, flat_atom_parser(&notes))
         }
+    }
 }
 
 fn maybe_yml_str_space<'a, E>() -> impl Parser<&'a str, Vec<char>, E>
@@ -128,7 +85,7 @@ where
     P: Parser<&'a str, FlatAtom, nom::error::Error<&'a str>>,
 {
     all_consuming(terminated(
-        many0(preceded(maybe_yml_str_space(), parser)),
+        many1(preceded(maybe_yml_str_space(), parser)),
         maybe_yml_str_space(),
     ))(input)
     .map_err(nom_err_message)