canload

provider/core/src/buf/serde.rs

@@ -13,7 +13,9 @@
 
 use crate::buf::BufferFormat;
 use crate::buf::BufferProvider;
+use crate::data_provider::DynamicCanLoad;
 use crate::prelude::*;
+use crate::CanLoad;
 use serde::de::Deserialize;
 use yoke::trait_hack::YokeTraitHack;
 use yoke::Yokeable;
@@ -149,7 +151,7 @@ impl DataPayload<BufferMarker> {
 impl<P, M> DynamicDataProvider<M> for DeserializingBufferProvider<'_, P>
 where
     M: DynamicDataMarker,
-    P: BufferProvider + ?Sized,
+    P: DynamicDataProvider<BufferMarker> + ?Sized,
     // Actual bound:
     //     for<'de> <M::Yokeable as Yokeable<'de>>::Output: serde::de::Deserialize<'de>,
     // Necessary workaround bound (see `yoke::trait_hack` docs):
@@ -184,10 +186,25 @@ where
     }
 }
 
+impl<P, M> DynamicCanLoad<M> for DeserializingBufferProvider<'_, P>
+where
+    M: DynamicDataMarker,
+    P: DynamicCanLoad<BufferMarker> + ?Sized,
+    // Actual bound:
+    //     for<'de> <M::Yokeable as Yokeable<'de>>::Output: serde::de::Deserialize<'de>,
+    // Necessary workaround bound (see `yoke::trait_hack` docs):
+    for<'de> YokeTraitHack<<M::Yokeable as Yokeable<'de>>::Output>: Deserialize<'de>,
+{
+    fn can_load_data(&self, marker: DataMarkerInfo, req: DataRequest) -> Result<bool, DataError> {
+        // Avoids deserialization, deserialization cannot produce `DataErrorKind::MissingLocale`
+        self.0.can_load_data(marker, req)
+    }
+}
+
 impl<P, M> DataProvider<M> for DeserializingBufferProvider<'_, P>
 where
     M: DataMarker,
-    P: BufferProvider + ?Sized,
+    P: DynamicDataProvider<BufferMarker> + ?Sized,
     // Actual bound:
     //     for<'de> <M::Yokeable as Yokeable<'de>>::Output: Deserialize<'de>,
     // Necessary workaround bound (see `yoke::trait_hack` docs):
@@ -206,6 +223,21 @@ where
     }
 }
 
+impl<P, M> CanLoad<M> for DeserializingBufferProvider<'_, P>
+where
+    M: DataMarker,
+    P: DynamicCanLoad<BufferMarker> + ?Sized,
+    // Actual bound:
+    //     for<'de> <M::Yokeable as Yokeable<'de>>::Output: Deserialize<'de>,
+    // Necessary workaround bound (see `yoke::trait_hack` docs):
+    for<'de> YokeTraitHack<<M::Yokeable as Yokeable<'de>>::Output>: Deserialize<'de>,
+{
+    fn can_load(&self, req: DataRequest) -> Result<bool, DataError> {
+        // Avoids deserialization, deserialization cannot produce `DataErrorKind::MissingLocale`
+        self.0.can_load_data(M::INFO, req)
+    }
+}
+
 #[cfg(feature = "deserialize_json")]
 impl From<serde_json::error::Error> for crate::DataError {
     fn from(e: serde_json::error::Error) -> Self {

provider/core/src/data_provider.rs

@@ -74,6 +74,23 @@ where
     }
 }
 
+/// A data provider that can determine whehter it can load a particular data identifier,
+/// potentially cheaper than performing the load.
+pub trait CanLoad<M: DataMarker>: DataProvider<M> {
+    /// This method returns false iff [`load`] fails with a [`DataErrorKind::IdentifierNotFound`].
+    ///
+    /// Other errors are returned as [`load`] would.
+    ///
+    /// [`load`]: DataProvider::load
+    fn can_load(&self, req: DataRequest) -> Result<bool, DataError> {
+        match self.load(req) {
+            Ok(_) => Ok(true),
+            Err(e) if e.kind == DataErrorKind::IdentifierNotFound => Ok(false),
+            Err(e) => Err(e),
+        }
+    }
+}
+
 /// A data provider that loads data for a specific data type.
 ///
 /// Unlike [`DataProvider`], there may be multiple markers corresponding to the same data type.
@@ -95,6 +112,23 @@ where
     ) -> Result<DataResponse<M>, DataError>;
 }
 
+/// A dynanmic data provider that can determine whehter it can load a particular data identifier,
+/// potentially cheaper than performing the load.
+pub trait DynamicCanLoad<M: DynamicDataMarker>: DynamicDataProvider<M> {
+    /// This method returns false iff [`load_data`] fails with a [`DataErrorKind::IdentifierNotFound`].
+    ///
+    /// Other errors are returned as [`load_data`] would.
+    ///
+    /// [`load_data`]: DynamicDataProvider::load_data
+    fn can_load_data(&self, marker: DataMarkerInfo, req: DataRequest) -> Result<bool, DataError> {
+        match self.load_data(marker, req) {
+            Ok(_) => Ok(true),
+            Err(e) if e.kind == DataErrorKind::IdentifierNotFound => Ok(false),
+            Err(e) => Err(e),
+        }
+    }
+}
+
 impl<'a, M, P> DynamicDataProvider<M> for &'a P
 where
     M: DynamicDataMarker,

provider/core/src/lib.rs

@@ -132,7 +132,8 @@ pub mod serde_borrow_de_utils;
 
 mod data_provider;
 pub use data_provider::{
-    BoundDataProvider, DataProvider, DataProviderWithMarker, DynamicDataProvider,
+    BoundDataProvider, CanLoad, DataProvider, DataProviderWithMarker, DynamicCanLoad,
+    DynamicDataProvider,
 };
 #[cfg(feature = "std")]
 pub use data_provider::{IterableDataProvider, IterableDynamicDataProvider};