1 files changed, 463 insertions, 0 deletions
diff --git a/tvix/serde/src/de.rs b/tvix/serde/src/de.rs
new file mode 100644
index 000000000000..2e8a9618e637
--- /dev/null
+++ b/tvix/serde/src/de.rs
@@ -0,0 +1,463 @@
+//! Deserialisation from Nix to Rust values.
+
+use serde::de::value::{MapDeserializer, SeqDeserializer};
+use serde::de::{self, EnumAccess, VariantAccess};
+pub use tvix_eval::Evaluation;
+use tvix_eval::Value;
+
+use crate::error::Error;
+
+struct NixDeserializer {
+    value: tvix_eval::Value,
+}
+
+impl NixDeserializer {
+    fn new(value: Value) -> Self {
+        if let Value::Thunk(thunk) = value {
+            Self::new(thunk.value().clone())
+        } else {
+            Self { value }
+        }
+    }
+}
+
+impl de::IntoDeserializer<'_, Error> for NixDeserializer {
+    type Deserializer = Self;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        self
+    }
+}
+
+/// Evaluate the Nix code in `src` and attempt to deserialise the
+/// value it returns to `T`.
+pub fn from_str<'code, T>(src: &'code str) -> Result<T, Error>
+where
+    T: serde::Deserialize<'code>,
+{
+    from_str_with_config(src, |_| /* no extra config */ ())
+}
+
+/// Evaluate the Nix code in `src`, with extra configuration for the
+/// `tvix_eval::Evaluation` provided by the given closure.
+pub fn from_str_with_config<'code, T, F>(src: &'code str, config: F) -> Result<T, Error>
+where
+    T: serde::Deserialize<'code>,
+    F: FnOnce(&mut Evaluation),
+{
+    // First step is to evaluate the Nix code ...
+    let mut eval = Evaluation::new(src, None);
+    config(&mut eval);
+
+    eval.strict = true;
+    let source = eval.source_map();
+    let result = eval.evaluate();
+
+    if !result.errors.is_empty() {
+        return Err(Error::NixErrors {
+            errors: result.errors,
+            source,
+        });
+    }
+
+    let de = NixDeserializer::new(result.value.expect("value should be present on success"));
+
+    T::deserialize(de)
+}
+
+fn unexpected(expected: &'static str, got: &Value) -> Error {
+    Error::UnexpectedType {
+        expected,
+        got: got.type_of(),
+    }
+}
+
+fn visit_integer<I: TryFrom<i64>>(v: &Value) -> Result<I, Error> {
+    match v {
+        Value::Integer(i) => I::try_from(*i).map_err(|_| Error::IntegerConversion {
+            got: *i,
+            need: std::any::type_name::<I>(),
+        }),
+
+        _ => Err(unexpected("integer", v)),
+    }
+}
+
+impl<'de> de::Deserializer<'de> for NixDeserializer {
+    type Error = Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            Value::Null => visitor.visit_unit(),
+            Value::Bool(b) => visitor.visit_bool(b),
+            Value::Integer(i) => visitor.visit_i64(i),
+            Value::Float(f) => visitor.visit_f64(f),
+            Value::String(s) => visitor.visit_string(s.to_string()),
+            Value::Path(p) => visitor.visit_string(p.to_string_lossy().into()), // TODO: hmm
+            Value::Attrs(_) => self.deserialize_map(visitor),
+            Value::List(_) => self.deserialize_seq(visitor),
+
+            // tvix-eval types that can not be deserialized through serde.
+            Value::Closure(_)
+            | Value::Builtin(_)
+            | Value::Thunk(_)
+            | Value::AttrNotFound
+            | Value::Blueprint(_)
+            | Value::DeferredUpvalue(_)
+            | Value::UnresolvedPath(_)
+            | Value::Json(_)
+            | Value::Catchable(_)
+            | Value::FinaliseRequest(_) => Err(Error::Unserializable {
+                value_type: self.value.type_of(),
+            }),
+        }
+    }
+
+    fn deserialize_bool<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            Value::Bool(b) => visitor.visit_bool(b),
+            _ => Err(unexpected("bool", &self.value)),
+        }
+    }
+
+    fn deserialize_i8<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_i8(visit_integer(&self.value)?)
+    }
+
+    fn deserialize_i16<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_i16(visit_integer(&self.value)?)
+    }
+
+    fn deserialize_i32<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_i32(visit_integer(&self.value)?)
+    }
+
+    fn deserialize_i64<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_i64(visit_integer(&self.value)?)
+    }
+
+    fn deserialize_u8<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_u8(visit_integer(&self.value)?)
+    }
+
+    fn deserialize_u16<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_u16(visit_integer(&self.value)?)
+    }
+
+    fn deserialize_u32<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_u32(visit_integer(&self.value)?)
+    }
+
+    fn deserialize_u64<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_u64(visit_integer(&self.value)?)
+    }
+
+    fn deserialize_f32<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if let Value::Float(f) = self.value {
+            return visitor.visit_f32(f as f32);
+        }
+
+        Err(unexpected("float", &self.value))
+    }
+
+    fn deserialize_f64<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if let Value::Float(f) = self.value {
+            return visitor.visit_f64(f);
+        }
+
+        Err(unexpected("float", &self.value))
+    }
+
+    fn deserialize_char<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if let Value::String(s) = &self.value {
+            let chars = s.as_str().chars().collect::<Vec<_>>();
+            if chars.len() == 1 {
+                return visitor.visit_char(chars[0]);
+            }
+        }
+
+        Err(unexpected("char", &self.value))
+    }
+
+    fn deserialize_str<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if let Value::String(s) = &self.value {
+            return visitor.visit_str(s.as_str());
+        }
+
+        Err(unexpected("string", &self.value))
+    }
+
+    fn deserialize_string<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if let Value::String(s) = &self.value {
+            return visitor.visit_str(s.as_str());
+        }
+
+        Err(unexpected("string", &self.value))
+    }
+
+    fn deserialize_bytes<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        unimplemented!()
+    }
+
+    fn deserialize_byte_buf<V>(self, _visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        unimplemented!()
+    }
+
+    // Note that this can not distinguish between a serialisation of
+    // `Some(())` and `None`.
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if let Value::Null = self.value {
+            visitor.visit_none()
+        } else {
+            visitor.visit_some(self)
+        }
+    }
+
+    fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if let Value::Null = self.value {
+            return visitor.visit_unit();
+        }
+
+        Err(unexpected("null", &self.value))
+    }
+
+    fn deserialize_unit_struct<V>(
+        self,
+        _name: &'static str,
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.deserialize_unit(visitor)
+    }
+
+    fn deserialize_newtype_struct<V>(
+        self,
+        _name: &'static str,
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_newtype_struct(self)
+    }
+
+    fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if let Value::List(list) = self.value {
+            let mut seq = SeqDeserializer::new(list.into_iter().map(NixDeserializer::new));
+            let result = visitor.visit_seq(&mut seq)?;
+            seq.end()?;
+            return Ok(result);
+        }
+
+        Err(unexpected("list", &self.value))
+    }
+
+    fn deserialize_tuple<V>(self, _len: usize, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        // just represent tuples as lists ...
+        self.deserialize_seq(visitor)
+    }
+
+    fn deserialize_tuple_struct<V>(
+        self,
+        _name: &'static str,
+        _len: usize,
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        // same as above
+        self.deserialize_seq(visitor)
+    }
+
+    fn deserialize_map<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        if let Value::Attrs(attrs) = self.value {
+            let mut map = MapDeserializer::new(attrs.into_iter().map(|(k, v)| {
+                (
+                    NixDeserializer::new(Value::String(k)),
+                    NixDeserializer::new(v),
+                )
+            }));
+            let result = visitor.visit_map(&mut map)?;
+            map.end()?;
+            return Ok(result);
+        }
+
+        Err(unexpected("map", &self.value))
+    }
+
+    fn deserialize_struct<V>(
+        self,
+        _name: &'static str,
+        _fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.deserialize_map(visitor)
+    }
+
+    // This method is responsible for deserializing the externally
+    // tagged enum variant serialisation.
+    fn deserialize_enum<V>(
+        self,
+        name: &'static str,
+        _variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            // a string represents a unit variant
+            Value::String(s) => visitor.visit_enum(de::value::StrDeserializer::new(s.as_str())),
+
+            // an attribute set however represents an externally
+            // tagged enum with content
+            Value::Attrs(attrs) => visitor.visit_enum(Enum(*attrs)),
+
+            _ => Err(unexpected(name, &self.value)),
+        }
+    }
+
+    fn deserialize_identifier<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.deserialize_str(visitor)
+    }
+
+    fn deserialize_ignored_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_unit()
+    }
+}
+
+struct Enum(tvix_eval::NixAttrs);
+
+impl<'de> EnumAccess<'de> for Enum {
+    type Error = Error;
+    type Variant = NixDeserializer;
+
+    // TODO: pass the known variants down here and check against them
+    fn variant_seed<V>(self, seed: V) -> Result<(V::Value, Self::Variant), Self::Error>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        if self.0.len() != 1 {
+            return Err(Error::AmbiguousEnum);
+        }
+
+        let (key, value) = self.0.into_iter().next().expect("length asserted above");
+        let val = seed.deserialize(de::value::StrDeserializer::<Error>::new(key.as_str()))?;
+
+        Ok((val, NixDeserializer::new(value)))
+    }
+}
+
+impl<'de> VariantAccess<'de> for NixDeserializer {
+    type Error = Error;
+
+    fn unit_variant(self) -> Result<(), Self::Error> {
+        // If this case is hit, a user specified the name of a unit
+        // enum variant but gave it content. Unit enum deserialisation
+        // is handled in `deserialize_enum` above.
+        Err(Error::UnitEnumContent)
+    }
+
+    fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value, Self::Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        seed.deserialize(self)
+    }
+
+    fn tuple_variant<V>(self, _len: usize, visitor: V) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        de::Deserializer::deserialize_seq(self, visitor)
+    }
+
+    fn struct_variant<V>(
+        self,
+        _fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Self::Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        de::Deserializer::deserialize_map(self, visitor)
+    }
+}