Implement Serde for Pattern (#4665)

utils/pattern/Cargo.toml

@@ -24,16 +24,20 @@ all-features = true
 displaydoc = { version = "0.2.3", default-features = false }
 writeable = { workspace = true }
 databake = { workspace = true, features = ["derive"], optional = true }
+serde = { version = "1.0", features = ["derive"], optional = true }
 yoke = { workspace = true, features = ["derive"], optional = true }
 zerofrom = { workspace = true, features = ["derive"], optional = true }
 
 [dev-dependencies]
 zerofrom = { workspace = true, features = ["alloc"] }
 zerovec = { workspace = true, features = ["databake", "serde"] }
+serde_json = { version = "1.0" }
+postcard = { version = "1.0", features = ["use-std"] }
 
 [features]
 alloc = []
 std = ["alloc"]
 databake = ["dep:databake"]
+serde = ["alloc", "dep:serde"]
 yoke = ["dep:yoke"]
 zerofrom = ["dep:zerofrom"]

utils/pattern/src/common.rs

@@ -32,7 +32,7 @@ pub enum PatternItem<'a, T> {
 #[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
 #[allow(clippy::exhaustive_enums)] // Part of core data model
 #[cfg(feature = "alloc")]
-#[cfg_attr(feature = "serde", derive(serde::Deserialize))]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 pub enum PatternItemCow<'a, T> {
     /// A placeholder of the type specified on this [`PatternItemCow`].
     Placeholder(T),
@@ -45,6 +45,16 @@ pub enum PatternItemCow<'a, T> {
     Literal(Cow<'a, str>),
 }
 
+#[cfg(feature = "alloc")]
+impl<'a, T> From<PatternItem<'a, T>> for PatternItemCow<'a, T> {
+    fn from(value: PatternItem<'a, T>) -> Self {
+        match value {
+            PatternItem::Placeholder(t) => Self::Placeholder(t),
+            PatternItem::Literal(s) => Self::Literal(Cow::Borrowed(s)),
+        }
+    }
+}
+
 /// Types that implement backing data models for [`Pattern`] implement this trait.
 ///
 /// The trait has no public methods and is not implementable outside of this crate.

utils/pattern/src/frontend/mod.rs

@@ -4,6 +4,8 @@
 
 #[cfg(feature = "databake")]
 mod databake;
+#[cfg(feature = "serde")]
+mod serde;
 
 use core::{
     fmt::{self, Write},

utils/pattern/src/frontend/serde.rs

@@ -0,0 +1,162 @@
+// This file is part of ICU4X. For terms of use, please see the file
+// called LICENSE at the top level of the ICU4X source tree
+// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
+
+use super::*;
+use alloc::borrow::Cow;
+use alloc::vec::Vec;
+use core::fmt::Display;
+
+use ::serde::{Deserialize, Deserializer, Serialize, Serializer};
+
+type HumanReadablePattern<'a, B> = Vec<PatternItemCow<'a, <B as PatternBackend>::PlaceholderKey>>;
+
+impl<'de, 'data, B, Store> Deserialize<'de> for Pattern<B, Store>
+where
+    'de: 'data,
+    B: PatternBackend,
+    B::Store: ToOwned + 'de,
+    &'de B::Store: Deserialize<'de>,
+    B::PlaceholderKey: Deserialize<'de>,
+    Store: TryFrom<Cow<'data, B::Store>> + AsRef<B::Store>,
+    Store::Error: Display,
+{
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        if deserializer.is_human_readable() {
+            let pattern_items = <HumanReadablePattern<B>>::deserialize(deserializer)?;
+            let pattern_owned: Pattern<B, <B::Store as ToOwned>::Owned> =
+                Pattern::try_from_items(pattern_items.into_iter())
+                    .map_err(<D::Error as ::serde::de::Error>::custom)?;
+            let pattern: Pattern<B, Store> = Pattern::from_store_unchecked(
+                Cow::<B::Store>::Owned(pattern_owned.take_store())
+                    .try_into()
+                    .map_err(<D::Error as ::serde::de::Error>::custom)?,
+            );
+            Ok(pattern)
+        } else {
+            let store = <&B::Store>::deserialize(deserializer)?;
+            let pattern = Self::try_from_store(
+                Cow::Borrowed(store)
+                    .try_into()
+                    .map_err(<D::Error as ::serde::de::Error>::custom)?,
+            )
+            .map_err(<D::Error as ::serde::de::Error>::custom)?;
+            Ok(pattern)
+        }
+    }
+}
+
+impl<B, Store> Serialize for Pattern<B, Store>
+where
+    B: PatternBackend,
+    B::Store: Serialize,
+    B::PlaceholderKey: Serialize,
+    Store: AsRef<B::Store>,
+{
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        if serializer.is_human_readable() {
+            let pattern_items: HumanReadablePattern<B> = B::iter_items(self.store.as_ref())
+                .map(|x| x.into())
+                .collect();
+            pattern_items.serialize(serializer)
+        } else {
+            let bytes = self.store.as_ref();
+            bytes.serialize(serializer)
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::SinglePlaceholderPattern;
+
+    #[test]
+    fn test_json() {
+        let pattern_owned = SinglePlaceholderPattern::try_from_str("Hello, {0}!").unwrap();
+        let pattern_cow: SinglePlaceholderPattern<Cow<str>> =
+            SinglePlaceholderPattern::from_store_unchecked(Cow::Owned(pattern_owned.take_store()));
+        let pattern_json = serde_json::to_string(&pattern_cow).unwrap();
+        assert_eq!(
+            pattern_json,
+            r#"[{"Literal":"Hello, "},{"Placeholder":"Singleton"},{"Literal":"!"}]"#
+        );
+        let pattern_deserialized: SinglePlaceholderPattern<Cow<str>> =
+            serde_json::from_str(&pattern_json).unwrap();
+        assert_eq!(pattern_cow, pattern_deserialized);
+        assert!(matches!(pattern_deserialized.take_store(), Cow::Owned(_)));
+    }
+
+    #[test]
+    fn test_postcard() {
+        let pattern_owned = SinglePlaceholderPattern::try_from_str("Hello, {0}!").unwrap();
+        let pattern_cow: SinglePlaceholderPattern<Cow<str>> =
+            SinglePlaceholderPattern::from_store_unchecked(Cow::Owned(pattern_owned.take_store()));
+        let pattern_postcard = postcard::to_stdvec(&pattern_cow).unwrap();
+        assert_eq!(pattern_postcard, b"\x09\x08Hello, !");
+        let pattern_deserialized: SinglePlaceholderPattern<Cow<str>> =
+            postcard::from_bytes(&pattern_postcard).unwrap();
+        assert_eq!(pattern_cow, pattern_deserialized);
+        assert!(matches!(
+            pattern_deserialized.take_store(),
+            Cow::Borrowed(_)
+        ));
+    }
+
+    macro_rules! check_store {
+        ($store:expr, $ty:ty) => {
+            check_store!(@borrow, $store, $ty);
+            let json = serde_json::to_string::<SinglePlaceholderPattern<$ty>>(
+                &SinglePlaceholderPattern::from_store_unchecked($store.clone()),
+            )
+            .unwrap();
+            let de_json = serde_json::from_str::<SinglePlaceholderPattern<$ty>>(&json).unwrap();
+            assert_eq!(de_json.take_store(), $store);
+        };
+        (@borrow, $store:expr, $ty:ty) => {
+            let postcard = postcard::to_stdvec::<SinglePlaceholderPattern<$ty>>(
+                &SinglePlaceholderPattern::from_store_unchecked($store.clone()),
+            )
+            .unwrap();
+            let de_postcard = postcard::from_bytes::<SinglePlaceholderPattern<$ty>>(&postcard).unwrap();
+            assert_eq!(de_postcard.take_store(), $store);
+        };
+    }
+
+    #[test]
+    fn test_serde_stores() {
+        let store = SinglePlaceholderPattern::try_from_str("Hello, {0}!")
+            .unwrap()
+            .take_store();
+
+        check_store!(Cow::Borrowed(store.as_str()), Cow<str>);
+        check_store!(Cow::<str>::Owned(store.clone()), Cow<str>);
+        check_store!(store.clone(), String);
+
+        /// A type implementing TryFrom<Cow<str>> that returns an error if the Cow is Owned
+        #[derive(Debug, Clone, PartialEq, displaydoc::Display)]
+        struct MyStr<'a>(&'a str);
+        impl<'a> TryFrom<Cow<'a, str>> for MyStr<'a> {
+            type Error = &'static str;
+            fn try_from(input: Cow<'a, str>) -> Result<MyStr<'a>, Self::Error> {
+                match input {
+                    Cow::Borrowed(s) => Ok(MyStr(s)),
+                    Cow::Owned(_) => Err("cannot borrow from a Cow with needed lifetime"),
+                }
+            }
+        }
+        impl AsRef<str> for MyStr<'_> {
+            fn as_ref(&self) -> &str {
+                self.0
+            }
+        }
+
+        check_store!(@borrow, MyStr(store.as_str()), MyStr);
+    }
+}

utils/pattern/src/single.rs

@@ -41,6 +41,7 @@ use alloc::string::String;
 /// );
 /// ```
 #[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 #[allow(clippy::exhaustive_enums)] // Singleton
 pub enum SinglePlaceholderKey {
     Singleton,

utils/pattern/tests/derive_test.rs

@@ -11,24 +11,56 @@ use icu_pattern::{Pattern, SinglePlaceholder};
 
 #[cfg_attr(feature = "yoke", derive(yoke::Yokeable))]
 #[cfg_attr(feature = "zerofrom", derive(zerofrom::ZeroFrom))]
-// #[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
+#[cfg_attr(feature = "serde", derive(serde::Deserialize, serde::Serialize))]
 #[cfg_attr(feature = "databake", derive(databake::Bake), databake(path = crate))]
-struct DeriveTest_SinglePlaceholderPattern_ZeroVec<'data> {
-    // #[cfg_attr(feature = "serde", serde(borrow))]
-    _data: Pattern<SinglePlaceholder, Cow<'data, str>>,
+#[derive(Debug, PartialEq)]
+struct DeriveTest_SinglePlaceholderPattern_Cow<'data> {
+    #[cfg_attr(feature = "serde", serde(borrow))]
+    data: Pattern<SinglePlaceholder, Cow<'data, str>>,
 }
 
 #[test]
 #[cfg(all(feature = "databake", feature = "alloc"))]
-fn bake_SinglePlaceholderPattern_ZeroVec() {
+fn bake_SinglePlaceholderPattern_Cow() {
     use databake::*;
     extern crate std;
     test_bake!(
-        DeriveTest_SinglePlaceholderPattern_ZeroVec<'static>,
-        crate::DeriveTest_SinglePlaceholderPattern_ZeroVec {
-            _data: icu_pattern::Pattern::<icu_pattern::SinglePlaceholder, _>::from_store_unchecked(
+        DeriveTest_SinglePlaceholderPattern_Cow<'static>,
+        crate::DeriveTest_SinglePlaceholderPattern_Cow {
+            data: icu_pattern::Pattern::<icu_pattern::SinglePlaceholder, _>::from_store_unchecked(
                 alloc::borrow::Cow::Borrowed(""),
             )
         },
     );
 }
+
+#[test]
+#[cfg(feature = "serde")]
+fn json_SinglePlaceholderPattern_Cow() {
+    let pattern_owned = Pattern::<SinglePlaceholder, String>::try_from_str("Hello, {0}!").unwrap();
+    let pattern_cow: Pattern<SinglePlaceholder, Cow<str>> =
+        Pattern::from_store_unchecked(Cow::Owned(pattern_owned.take_store()));
+    let data = DeriveTest_SinglePlaceholderPattern_Cow { data: pattern_cow };
+    let data_json = serde_json::to_string(&data).unwrap();
+    assert_eq!(
+        data_json,
+        r#"{"data":[{"Literal":"Hello, "},{"Placeholder":"Singleton"},{"Literal":"!"}]}"#
+    );
+    let data_deserialized: DeriveTest_SinglePlaceholderPattern_Cow =
+        serde_json::from_str(&data_json).unwrap();
+    assert_eq!(data, data_deserialized);
+}
+
+#[test]
+#[cfg(feature = "serde")]
+fn postcard_SinglePlaceholderPattern_Cow() {
+    let pattern_owned = Pattern::<SinglePlaceholder, String>::try_from_str("Hello, {0}!").unwrap();
+    let pattern_cow: Pattern<SinglePlaceholder, Cow<str>> =
+        Pattern::from_store_unchecked(Cow::Owned(pattern_owned.take_store()));
+    let data = DeriveTest_SinglePlaceholderPattern_Cow { data: pattern_cow };
+    let data_postcard = postcard::to_stdvec(&data).unwrap();
+    assert_eq!(data_postcard, b"\x09\x08Hello, !");
+    let data_deserialized: DeriveTest_SinglePlaceholderPattern_Cow =
+        postcard::from_bytes(&data_postcard).unwrap();
+    assert_eq!(data, data_deserialized);
+}