perf(json5): Remove use of serde(untagged)

Prep for rust-cli#472

Author: epage

Cargo.lock

@@ -125,7 +125,7 @@ default = ["toml", "json", "yaml", "ini", "ron", "json5", "convert-case", "async
 json = ["serde_json"]
 yaml = ["yaml-rust2"]
 ini = ["rust-ini"]
-json5 = ["json5_rs", "serde/derive"]
+json5 = ["json5_rs", "dep:serde-untagged"]
 convert-case = ["convert_case"]
 preserve_order = ["indexmap", "toml?/preserve_order", "serde_json?/preserve_order", "ron?/indexmap"]
 async = ["async-trait"]
@@ -145,6 +145,7 @@ indexmap = { version = "2.10.0", features = ["serde"], optional = true }
 convert_case = { version = "0.6", optional = true }
 pathdiff = "0.2"
 winnow = "0.7.0"
+serde-untagged = { version = "0.1.8", optional = true }
 
 [dev-dependencies]
 serde_derive = "1.0"

Cargo.toml

@@ -4,8 +4,7 @@ use crate::format;
 use crate::map::Map;
 use crate::value::{Value, ValueKind};
 
-#[derive(serde::Deserialize, Debug)]
-#[serde(untagged)]
+#[derive(Debug)]
 pub(crate) enum Val {
     Null,
     Boolean(bool),
@@ -16,6 +15,23 @@ pub(crate) enum Val {
     Object(Map<String, Self>),
 }
 
+impl<'de> serde::de::Deserialize<'de> for Val {
+    fn deserialize<D>(d: D) -> Result<Self, D::Error>
+    where
+        D: serde::de::Deserializer<'de>,
+    {
+        serde_untagged::UntaggedEnumVisitor::new()
+            .bool(|value| Ok(Self::Boolean(value)))
+            .i64(|value| Ok(Self::Integer(value)))
+            .f64(|value| Ok(Self::Float(value)))
+            .string(|value| Ok(Val::String(value.to_owned())))
+            .none(|| Ok(Self::Null))
+            .seq(|value| value.deserialize().map(Val::Array))
+            .map(|value| value.deserialize().map(Val::Object))
+            .deserialize(d)
+    }
+}
+
 pub(crate) fn parse(
     uri: Option<&String>,
     text: &str,

src/file/format/json5.rs

@@ -676,8 +676,6 @@ impl ser::SerializeStructVariant for Unreachable {
 
 #[cfg(test)]
 mod test {
-    use serde::{Deserialize, Serialize};
-    #[cfg(not(feature = "json5"))]
     use serde_derive::{Deserialize, Serialize};
 
     use super::*;