Add PhantomData databake impl

CHANGELOG.md

@@ -42,6 +42,8 @@
         - Add Keviyah/Four Gates based optimized calculations module for the Hebrew calendar. (https://github.com/unicode-org/icu4x/pull/4504)
         - Expose `Hebrew` as a unit struct, add `Date::try_new_hebrew_date()`, `DateTime::try_new_hebrew_datetime()`. (https://github.com/unicode-org/icu4x/pulls/4532)
         - Deprecate `Hebrew::new_always_precomputing()`, `Date::try_new_hebrew_date_with_calendar()`, `DateTime::try_new_hebrew_datetime_with_calendar()`. The new implementation of the Hebrew calendar is faster and we do not need APIs for precomputation. (https://github.com/unicode-org/icu4x/pulls/4532)
+    - `databake`
+        - Add `impl Bake for PhantomData<T>` (https://github.com/unicode-org/icu4x/pull/4663)
     - `litemap`
         - Add `impl IntoIterator for LiteMap` by splitting `StoreIterableMut` trait (https://github.com/unicode-org/icu4x/pull/4359)
     - `yoke`

utils/databake/src/primitives.rs

@@ -2,6 +2,8 @@
 // called LICENSE at the top level of the ICU4X source tree
 // (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
 
+use std::marker::PhantomData;
+
 use super::*;
 
 macro_rules! literal {
@@ -255,3 +257,19 @@ fn tuple() {
         const: (0u8, 0i8)
     );
 }
+
+impl<T> Bake for PhantomData<T> {
+    fn bake(&self, _ctx: &CrateEnv) -> TokenStream {
+        quote! {
+            ::core::marker::PhantomData
+        }
+    }
+}
+
+#[test]
+fn phantom_data() {
+    test_bake!(
+        PhantomData<usize>,
+        const: ::core::marker::PhantomData
+    );
+}