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/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::*;