feat: splitting

src/util/yaml.rs

@@ -16,7 +16,7 @@ use std::fs;
 use std::path::Path;
 
 use serde::de::{self, DeserializeOwned, Visitor};
-use serde::{Deserializer, Serialize};
+use serde::{Deserialize, Deserializer, Serialize};
 
 use crate::error::{Error, Result};
 
@@ -61,6 +61,26 @@ pub fn write<T: Serialize>(path: &Path, value: &T) -> Result<()> {
     fs::write(path, text).map_err(|e| Error::io(path, e))
 }
 
+/// Serializes a value to a YAML string.
+///
+/// Used where the caller needs to put something in front of the document, such
+/// as the banner on a generated file.
+///
+/// # Arguments
+///
+/// * `value` - the value to serialize.
+///
+/// # Returns
+///
+/// The YAML text.
+///
+/// # Errors
+///
+/// Returns [`Error::Other`] if the value cannot be represented as YAML.
+pub fn to_string<T: Serialize>(value: &T) -> Result<String> {
+    serde_yaml_ng::to_string(value).map_err(Error::other)
+}
+
 /// Deserializes a JSON file into any type.
 ///
 /// Used only for importing legacy banks and for reading emitted schemas back in
@@ -202,6 +222,33 @@ where
     d.deserialize_any(V)
 }
 
+/// Deserializes an optional scalar as a string, quoted or not.
+///
+/// The [`flexible_string`] of a field that may be absent, which is what a
+/// fragment's `schema_version` is: one file in a course declares it and the
+/// rest inherit.
+///
+/// # Arguments
+///
+/// * `d` - the deserializer.
+///
+/// # Returns
+///
+/// The value as a string, or `None`.
+///
+/// # Errors
+///
+/// Returns a deserialization error for non-scalar input.
+pub fn flexible_string_opt<'de, D>(d: D) -> std::result::Result<Option<String>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    #[derive(serde::Deserialize)]
+    struct Wrapper(#[serde(deserialize_with = "flexible_string")] String);
+
+    Ok(Option::<Wrapper>::deserialize(d)?.map(|w| w.0))
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;