feat(tvix/eval): implement serde::Deserialize for Value

Co-Authored-By: Vincent Ambo <tazjin@tvl.su>

Change-Id: Ib6f7d1f4f4faac36b44f5f75cccc57bf912cf606
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7626
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

tvix/eval/src/value/attrs.rs

@@ -8,6 +8,8 @@
 use std::iter::FromIterator;
 
 use imbl::{ordmap, OrdMap};
+use serde::de::{Deserializer, Error, Visitor};
+use serde::Deserialize;
 
 use crate::errors::ErrorKind;
 use crate::vm::VM;
@@ -20,7 +22,7 @@ use super::Value;
 #[cfg(test)]
 mod tests;
 
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Deserialize)]
 enum AttrsRep {
     Empty,
 
@@ -138,6 +140,39 @@ impl TotalDisplay for NixAttrs {
     }
 }
 
+impl<'de> Deserialize<'de> for NixAttrs {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct MapVisitor;
+
+        impl<'de> Visitor<'de> for MapVisitor {
+            type Value = NixAttrs;
+
+            fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
+                formatter.write_str("a valid Nix attribute set")
+            }
+
+            fn visit_map<A>(self, mut map: A) -> Result<Self::Value, A::Error>
+            where
+                A: serde::de::MapAccess<'de>,
+            {
+                let mut stack_array = Vec::with_capacity(map.size_hint().unwrap_or(0) * 2);
+
+                while let Some((key, value)) = map.next_entry()? {
+                    stack_array.push(key);
+                    stack_array.push(value);
+                }
+
+                NixAttrs::construct(stack_array.len() / 2, stack_array).map_err(A::Error::custom)
+            }
+        }
+
+        deserializer.deserialize_map(MapVisitor)
+    }
+}
+
 #[cfg(feature = "arbitrary")]
 mod arbitrary {
     use super::*;

tvix/eval/src/value/list.rs

@@ -3,6 +3,8 @@ use std::ops::Index;
 
 use imbl::{vector, Vector};
 
+use serde::Deserialize;
+
 use crate::errors::ErrorKind;
 use crate::vm::VM;
 
@@ -11,7 +13,7 @@ use super::TotalDisplay;
 use super::Value;
 
 #[repr(transparent)]
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Deserialize)]
 pub struct NixList(Vector<Value>);
 
 impl TotalDisplay for NixList {

tvix/eval/src/value/mod.rs

@@ -6,6 +6,8 @@ use std::path::PathBuf;
 use std::rc::Rc;
 use std::{cell::Ref, fmt::Display};
 
+use serde::Deserialize;
+
 #[cfg(feature = "arbitrary")]
 mod arbitrary;
 mod attrs;
@@ -31,30 +33,41 @@ pub use thunk::Thunk;
 use self::thunk::ThunkSet;
 
 #[warn(variant_size_differences)]
-#[derive(Clone, Debug)]
+#[derive(Clone, Debug, Deserialize)]
+#[serde(untagged)]
 pub enum Value {
     Null,
     Bool(bool),
     Integer(i64),
     Float(f64),
     String(NixString),
+
+    #[serde(skip)]
     Path(PathBuf),
     Attrs(Box<NixAttrs>),
     List(NixList),
+
+    #[serde(skip)]
     Closure(Rc<Closure>), // must use Rc<Closure> here in order to get proper pointer equality
+    #[serde(skip)]
     Builtin(Builtin),
 
     // Internal values that, while they technically exist at runtime,
     // are never returned to or created directly by users.
+    #[serde(skip)]
     Thunk(Thunk),
 
     // See [`compiler::compile_select_or()`] for explanation
+    #[serde(skip)]
     AttrNotFound,
 
     // this can only occur in Chunk::Constants and nowhere else
+    #[serde(skip)]
     Blueprint(Rc<Lambda>),
 
+    #[serde(skip)]
     DeferredUpvalue(StackIdx),
+    #[serde(skip)]
     UnresolvedPath(PathBuf),
 }
 
@@ -542,47 +555,9 @@ impl From<PathBuf> for Value {
     }
 }
 
-impl TryFrom<serde_json::Value> for Value {
-    type Error = ErrorKind;
-
-    fn try_from(value: serde_json::Value) -> Result<Self, Self::Error> {
-        // TODO(grfn): Replace with a real serde::Deserialize impl (for perf)
-        match value {
-            serde_json::Value::Null => Ok(Self::Null),
-            serde_json::Value::Bool(b) => Ok(Self::Bool(b)),
-            serde_json::Value::Number(n) => {
-                if let Some(i) = n.as_i64() {
-                    Ok(Self::Integer(i))
-                } else if let Some(f) = n.as_f64() {
-                    Ok(Self::Float(f))
-                } else {
-                    Err(ErrorKind::FromJsonError(format!(
-                        "JSON number not representable as Nix value: {n}"
-                    )))
-                }
-            }
-            serde_json::Value::String(s) => Ok(s.into()),
-            serde_json::Value::Array(a) => Ok(Value::List(
-                a.into_iter()
-                    .map(Value::try_from)
-                    .collect::<Result<imbl::Vector<_>, _>>()?
-                    .into(),
-            )),
-            serde_json::Value::Object(obj) => {
-                match (obj.len(), obj.get("name"), obj.get("value")) {
-                    (2, Some(name), Some(value)) => Ok(Self::attrs(NixAttrs::from_kv(
-                        name.clone().try_into()?,
-                        value.clone().try_into()?,
-                    ))),
-                    _ => Ok(Self::attrs(NixAttrs::from_iter(
-                        obj.into_iter()
-                            .map(|(k, v)| Ok((k.into(), v.try_into()?)))
-                            .collect::<Result<Vec<(NixString, Value)>, ErrorKind>>()?
-                            .into_iter(),
-                    ))),
-                }
-            }
-        }
+impl From<Vec<Value>> for Value {
+    fn from(val: Vec<Value>) -> Self {
+        Self::List(NixList::from_vec(val))
     }
 }
 

tvix/eval/src/value/string.rs

@@ -8,6 +8,9 @@ use std::ops::Deref;
 use std::path::Path;
 use std::{borrow::Cow, fmt::Display, str::Chars};
 
+use serde::de::{Deserializer, Visitor};
+use serde::Deserialize;
+
 #[derive(Clone, Debug)]
 enum StringRepr {
     Smol(SmolStr),
@@ -68,6 +71,39 @@ impl Hash for NixString {
     }
 }
 
+impl<'de> Deserialize<'de> for NixString {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct StringVisitor;
+
+        impl<'de> Visitor<'de> for StringVisitor {
+            type Value = NixString;
+
+            fn expecting(&self, formatter: &mut std::fmt::Formatter) -> std::fmt::Result {
+                formatter.write_str("a valid Nix string")
+            }
+
+            fn visit_string<E>(self, v: String) -> Result<Self::Value, E>
+            where
+                E: serde::de::Error,
+            {
+                Ok(v.into())
+            }
+
+            fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+            where
+                E: serde::de::Error,
+            {
+                Ok(v.into())
+            }
+        }
+
+        deserializer.deserialize_string(StringVisitor)
+    }
+}
+
 #[cfg(feature = "arbitrary")]
 mod arbitrary {
     use super::*;