fix: tweak bounds on For for backwards-compat (#3663)

Cargo.lock

@@ -1808,6 +1808,7 @@ dependencies = [
  "send_wrapper",
  "serde_json",
  "server_fn",
+ "tachys",
  "tokio",
  "tracing",
 ]
@@ -1829,6 +1830,7 @@ dependencies = [
  "once_cell",
  "parking_lot",
  "server_fn",
+ "tachys",
  "tokio",
  "tower",
  "tower-http",
@@ -3450,6 +3452,8 @@ dependencies = [
  "reactive_stores",
  "rustc-hash 2.1.1",
  "send_wrapper",
+ "serde",
+ "serde_json",
  "sledgehammer_bindgen",
  "sledgehammer_utils",
  "slotmap",

integrations/actix/Cargo.toml

@@ -21,6 +21,7 @@ leptos_macro = { workspace = true, features = ["actix"] }
 leptos_meta = { workspace = true, features = ["nonce"] }
 leptos_router = { workspace = true, features = ["ssr"] }
 server_fn = { workspace = true, features = ["actix"] }
+tachys = { workspace = true }
 serde_json = { workspace = true }
 parking_lot = "0.12.3"
 tracing = { version = "0.1", optional = true }
@@ -33,7 +34,7 @@ once_cell = "1"
 rustdoc-args = ["--generate-link-to-definition"]
 
 [features]
-islands-router = []
+islands-router = ["tachys/islands"]
 tracing = ["dep:tracing"]
 
 [package.metadata.cargo-all-features]

integrations/axum/Cargo.toml

@@ -22,6 +22,7 @@ leptos_macro = { workspace = true, features = ["axum"] }
 leptos_meta = { workspace = true, features = ["ssr", "nonce"] }
 leptos_router = { workspace = true, features = ["ssr"] }
 leptos_integration_utils = { workspace = true }
+tachys = { workspace = true }
 once_cell = "1"
 parking_lot = "0.12.3"
 tokio = { version = "1.43", default-features = false }
@@ -36,7 +37,7 @@ tokio = { version = "1.43", features = ["net", "rt-multi-thread"] }
 [features]
 wasm = []
 default = ["tokio/fs", "tokio/sync", "tower-http/fs", "tower/util"]
-islands-router = []
+islands-router = ["tachys/islands"]
 tracing = ["dep:tracing"]
 
 [package.metadata.docs.rs]

leptos/src/for_loop.rs

@@ -6,7 +6,10 @@ use reactive_graph::{
     traits::Set,
 };
 use std::hash::Hash;
-use tachys::{reactive_graph::OwnedView, view::keyed::keyed};
+use tachys::{
+    reactive_graph::OwnedView,
+    view::keyed::{keyed, SerializableKey},
+};
 
 /// Iterates over children and displays them, keyed by the `key` function given.
 ///
@@ -121,7 +124,7 @@ where
     EF: Fn(T) -> N + Send + Clone + 'static,
     N: IntoView + 'static,
     KF: Fn(&T) -> K + Send + Clone + 'static,
-    K: Eq + Hash + ToString + 'static,
+    K: Eq + Hash + SerializableKey + 'static,
     T: Send + 'static,
 {
     // this takes the owner of the For itself
@@ -195,7 +198,7 @@ where
     EF: Fn(ReadSignal<usize>, T) -> N + Send + Clone + 'static,
     N: IntoView + 'static,
     KF: Fn(&T) -> K + Send + Clone + 'static,
-    K: Eq + Hash + ToString + 'static,
+    K: Eq + Hash + SerializableKey + 'static,
     T: Send + 'static,
 {
     // this takes the owner of the For itself
@@ -218,6 +221,7 @@ where
     };
     move || keyed(each(), key.clone(), children.clone())
 }
+
 /*
 #[cfg(test)]
 mod tests {

tachys/Cargo.toml

@@ -162,6 +162,8 @@ sledgehammer_bindgen = { version = "0.6.0", features = [
 ], optional = true }
 sledgehammer_utils = { version = "0.3.1", optional = true }
 tracing = { version = "0.1.41", optional = true }
+serde = { version = "1", optional = true }
+serde_json = { version = "1", optional = true }
 
 [dev-dependencies]
 tokio-test = "0.4.4"
@@ -172,7 +174,7 @@ default = ["testing"]
 delegation = []                                                       # enables event delegation
 error-hook = []
 hydrate = []
-islands = []
+islands = ["dep:serde", "dep:serde_json"]
 ssr = []
 oco = ["dep:oco_ref"]
 nightly = ["reactive_graph/nightly"]

tachys/src/view/keyed.rs

@@ -50,6 +50,39 @@ where
     view_fn: VF,
 }
 
+/// By default, keys used in for keyed iteration do not need to be serializable.
+///
+/// However, for some scenarios (like the “islands routing” mode that mixes server-side
+/// rendering with client-side navigation) it is useful to have serializable keys.
+///
+/// When the `islands` feature is not enabled, this trait is implemented by all types.
+///
+/// When the `islands` features is enabled, this is automatically implemented for all types
+/// that implement [`Serialize`](serde::Serialize), and can be manually implemented otherwise.
+pub trait SerializableKey {
+    /// Serializes the key to a unique string.
+    ///
+    /// The string can have any value, as long as it is idempotent (i.e., serializing the same key
+    /// multiple times will give the same value).
+    fn ser_key(&self) -> String;
+}
+
+#[cfg(not(feature = "islands"))]
+impl<T> SerializableKey for T {
+    fn ser_key(&self) -> String {
+        panic!(
+            "SerializableKey called without the `islands` feature enabled. \
+             Something has gone wrong."
+        );
+    }
+}
+#[cfg(feature = "islands")]
+impl<T: serde::Serialize> SerializableKey for T {
+    fn ser_key(&self) -> String {
+        serde_json::to_string(self).expect("failed to serialize key")
+    }
+}
+
 /// Retained view state for a keyed list.
 pub struct KeyedState<K, VFS, V>
 where
@@ -66,7 +99,7 @@ where
 impl<T, I, K, KF, VF, VFS, V> Render for Keyed<T, I, K, KF, VF, VFS, V>
 where
     I: IntoIterator<Item = T>,
-    K: Eq + Hash + ToString + 'static,
+    K: Eq + Hash + SerializableKey + 'static,
     KF: Fn(&T) -> K,
     V: Render,
     VF: Fn(usize, T) -> (VFS, V),
@@ -132,7 +165,7 @@ where
 impl<T, I, K, KF, VF, VFS, V> AddAnyAttr for Keyed<T, I, K, KF, VF, VFS, V>
 where
     I: IntoIterator<Item = T> + Send + 'static,
-    K: Eq + Hash + ToString + 'static,
+    K: Eq + Hash + SerializableKey + 'static,
     KF: Fn(&T) -> K + Send + 'static,
     V: RenderHtml,
     V: 'static,
@@ -185,7 +218,7 @@ where
 impl<T, I, K, KF, VF, VFS, V> RenderHtml for Keyed<T, I, K, KF, VF, VFS, V>
 where
     I: IntoIterator<Item = T> + Send + 'static,
-    K: Eq + Hash + ToString + 'static,
+    K: Eq + Hash + SerializableKey + 'static,
     KF: Fn(&T) -> K + Send + 'static,
     V: RenderHtml + 'static,
     VF: Fn(usize, T) -> (VFS, V) + Send + 'static,
@@ -261,7 +294,7 @@ where
         for (index, item) in self.items.into_iter().enumerate() {
             let branch_name = mark_branches.then(|| {
                 let key = (self.key_fn)(&item);
-                let key = key.to_string();
+                let key = key.ser_key();
                 format!("item-{key}")
             });
             let (_, item) = (self.view_fn)(index, item);