From 41c213a618d4de47c76ed477b2949d738a595d9f Mon Sep 17 00:00:00 2001
From: Bilal Mahmoud <bmahmoud@mpi-cbg.de>
Date: Sun, 9 Apr 2023 18:51:38 +0200
Subject: [PATCH 1/2] chore: convert from #1875

---
 libs/deer/src/impls/core.rs        |  1 +
 libs/deer/src/impls/core/marker.rs | 45 ++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)
 create mode 100644 libs/deer/src/impls/core/marker.rs

diff --git a/libs/deer/src/impls/core.rs b/libs/deer/src/impls/core.rs
index 4e08ee1bf35..538ffa6c6d1 100644
--- a/libs/deer/src/impls/core.rs
+++ b/libs/deer/src/impls/core.rs
@@ -3,6 +3,7 @@ mod atomic;
 mod bool;
 mod floating;
 mod integral;
+mod marker;
 mod non_zero;
 mod string;
 mod unit;
diff --git a/libs/deer/src/impls/core/marker.rs b/libs/deer/src/impls/core/marker.rs
new file mode 100644
index 00000000000..24abd0a6129
--- /dev/null
+++ b/libs/deer/src/impls/core/marker.rs
@@ -0,0 +1,45 @@
+use core::marker::PhantomData;
+
+use error_stack::{Result, ResultExt};
+
+use crate::{
+    error::{DeserializeError, VisitorError},
+    Deserialize, Deserializer, Document, Reflection, Schema, Visitor,
+};
+
+struct PhantomDataVisitor<T: ?Sized>(PhantomData<T>);
+
+impl<'de, T: ?Sized> Visitor<'de> for PhantomDataVisitor<T> {
+    type Value = PhantomData<T>;
+
+    fn expecting(&self) -> Document {
+        Self::Value::reflection()
+    }
+
+    fn visit_none(self) -> Result<Self::Value, VisitorError> {
+        Ok(PhantomData)
+    }
+
+    fn visit_null(self) -> Result<Self::Value, VisitorError> {
+        Ok(PhantomData)
+    }
+}
+
+pub struct PhantomDataReflection;
+
+impl Reflection for PhantomDataReflection {
+    fn schema(_: &mut Document) -> Schema {
+        // TODO: this is also optional (none)
+        //  currently we're unable to express that constraint (something for 0.2)
+        Schema::new("null")
+    }
+}
+
+impl<'de, T: ?Sized> Deserialize<'de> for PhantomData<T> {
+    type Reflection = PhantomDataReflection;
+
+    fn deserialize<D: Deserializer<'de>>(de: D) -> Result<Self, DeserializeError> {
+        de.deserialize_null(PhantomDataVisitor(PhantomData))
+            .change_context(DeserializeError)
+    }
+}

From a871ffeee6930b338978b030e9a785093c215e37 Mon Sep 17 00:00:00 2001
From: Bilal Mahmoud <bmahmoud@mpi-cbg.de>
Date: Sun, 9 Apr 2023 18:56:58 +0200
Subject: [PATCH 2/2] test: `PhantomData`

---
 libs/deer/src/impls/core/marker.rs        | 2 +-
 libs/deer/tests/test_impls_core_marker.rs | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)
 create mode 100644 libs/deer/tests/test_impls_core_marker.rs

diff --git a/libs/deer/src/impls/core/marker.rs b/libs/deer/src/impls/core/marker.rs
index 24abd0a6129..ebd68f9f72b 100644
--- a/libs/deer/src/impls/core/marker.rs
+++ b/libs/deer/src/impls/core/marker.rs
@@ -39,7 +39,7 @@ impl<'de, T: ?Sized> Deserialize<'de> for PhantomData<T> {
     type Reflection = PhantomDataReflection;
 
     fn deserialize<D: Deserializer<'de>>(de: D) -> Result<Self, DeserializeError> {
-        de.deserialize_null(PhantomDataVisitor(PhantomData))
+        de.deserialize_null(PhantomDataVisitor(Self))
             .change_context(DeserializeError)
     }
 }
diff --git a/libs/deer/tests/test_impls_core_marker.rs b/libs/deer/tests/test_impls_core_marker.rs
new file mode 100644
index 00000000000..fb1c8076c1e
--- /dev/null
+++ b/libs/deer/tests/test_impls_core_marker.rs
@@ -0,0 +1,8 @@
+use core::marker::PhantomData;
+
+use deer_desert::{assert_tokens, Token};
+
+#[test]
+fn phantom_data_ok() {
+    assert_tokens::<PhantomData<u64>>(&PhantomData, &[Token::Null]);
+}