Replace TryFrom with custom TryFromJsValue trait (#3709)

CHANGELOG.md

@@ -16,6 +16,9 @@
 * The DWARF section is now correctly modified instead of leaving it in a broken state.
   [#3483](https://github.com/rustwasm/wasm-bindgen/pull/3483)
 
+* Fixed an issue where `#[wasm_bindgen]` automatically derived the `TryFrom` trait for any struct, preventing custom `TryFrom<JsValue>` implementations. It has been updated to utilize a new `TryFromJsValue` trait instead.
+  [#3709](https://github.com/rustwasm/wasm-bindgen/pull/3709)
+
 * Update the TypeScript signature of `__wbindgen_thread_destroy` to indicate that it's parameters are optional.
   [#3703](https://github.com/rustwasm/wasm-bindgen/pull/3703)
 

crates/backend/src/codegen.rs

@@ -297,10 +297,10 @@ impl ToTokens for ast::Struct {
             }
 
             #[allow(clippy::all)]
-            impl #wasm_bindgen::__rt::core::convert::TryFrom<#wasm_bindgen::JsValue> for #name {
+            impl #wasm_bindgen::convert::TryFromJsValue for #name {
                 type Error = #wasm_bindgen::JsValue;
 
-                fn try_from(value: #wasm_bindgen::JsValue)
+                fn try_from_js_value(value: #wasm_bindgen::JsValue)
                     -> #wasm_bindgen::__rt::std::result::Result<Self, Self::Error> {
                     let idx = #wasm_bindgen::convert::IntoWasmAbi::into_abi(&value);
 
@@ -819,6 +819,7 @@ impl ToTokens for ast::ImportType {
 
             #[automatically_derived]
             const _: () = {
+                use #wasm_bindgen::convert::TryFromJsValue;
                 use #wasm_bindgen::convert::{IntoWasmAbi, FromWasmAbi};
                 use #wasm_bindgen::convert::{OptionIntoWasmAbi, OptionFromWasmAbi};
                 use #wasm_bindgen::convert::{RefFromWasmAbi, LongRefFromWasmAbi};
@@ -1452,11 +1453,12 @@ impl ToTokens for ast::Enum {
             }
 
             #[allow(clippy::all)]
-            impl #wasm_bindgen::__rt::core::convert::TryFrom<#wasm_bindgen::JsValue> for #enum_name {
+            impl #wasm_bindgen::convert::TryFromJsValue for #enum_name {
                 type Error = #wasm_bindgen::JsValue;
 
-                fn try_from(value: #wasm_bindgen::JsValue)
-                    -> #wasm_bindgen::__rt::std::result::Result<Self, <#enum_name as #wasm_bindgen::__rt::core::convert::TryFrom<JsValue>>::Error> {
+                fn try_from_js_value(value: #wasm_bindgen::JsValue)
+                    -> #wasm_bindgen::__rt::std::result::Result<Self, <#enum_name as #wasm_bindgen::convert::TryFromJsValue>::Error> {
+                    use #wasm_bindgen::__rt::core::convert::TryFrom;
                     let js = f64::try_from(&value)? as u32;
 
                     #wasm_bindgen::__rt::std::result::Result::Ok(

src/convert/impls.rs

@@ -2,13 +2,13 @@ use core::char;
 use core::mem::{self, ManuallyDrop};
 
 use crate::convert::traits::{WasmAbi, WasmPrimitive};
+use crate::convert::TryFromJsValue;
 use crate::convert::{FromWasmAbi, IntoWasmAbi, LongRefFromWasmAbi, RefFromWasmAbi};
 use crate::convert::{OptionFromWasmAbi, OptionIntoWasmAbi, ReturnWasmAbi};
 use crate::{Clamped, JsError, JsValue, UnwrapThrowExt};
 
 if_std! {
     use std::boxed::Box;
-    use std::convert::{TryFrom, TryInto};
     use std::fmt::Debug;
     use std::vec::Vec;
 }
@@ -415,7 +415,7 @@ if_std! {
         js_vals.into_abi()
     }
 
-    pub unsafe fn js_value_vector_from_abi<T: TryFrom<JsValue>>(js: <Box<[JsValue]> as FromWasmAbi>::Abi) -> Box<[T]> where T::Error: Debug {
+    pub unsafe fn js_value_vector_from_abi<T: TryFromJsValue>(js: <Box<[JsValue]> as FromWasmAbi>::Abi) -> Box<[T]> where T::Error: Debug {
         let js_vals = <Vec<JsValue> as FromWasmAbi>::from_abi(js);
 
         let mut result = Vec::with_capacity(js_vals.len());
@@ -430,7 +430,7 @@ if_std! {
             // we're talking about, it can only see functions that actually make it to the
             // final wasm binary (i.e., not inlined functions). All of those internal
             // iterator functions get inlined in release mode, and so they don't show up.
-            result.push(value.try_into().expect_throw("array contains a value of the wrong type"));
+            result.push(T::try_from_js_value(value).expect_throw("array contains a value of the wrong type"));
         }
         result.into_boxed_slice()
     }

src/convert/traits.rs

@@ -2,6 +2,7 @@ use core::borrow::Borrow;
 use core::ops::{Deref, DerefMut};
 
 use crate::describe::*;
+use crate::JsValue;
 
 /// A trait for anything that can be converted into a type that can cross the
 /// wasm ABI directly, eg `u32` or `f64`.
@@ -249,3 +250,18 @@ impl<T: WasmAbi> WasmRet<T> {
         T::join(self.prim1, self.prim2, self.prim3, self.prim4)
     }
 }
+
+/// [`TryFromJsValue`] is a trait for converting a JavaScript value ([`JsValue`])
+/// into a Rust type. It is used by the [`wasm_bindgen`](wasm_bindgen_macro::wasm_bindgen)
+/// proc-macro to allow conversion to user types.
+///
+/// Types implementing this trait must specify their conversion logic from
+/// [`JsValue`] to the Rust type, handling any potential errors that may occur
+/// during the conversion process.
+pub trait TryFromJsValue: Sized {
+    /// The type returned in the event of a conversion error.
+    type Error;
+
+    /// Performs the conversion.
+    fn try_from_js_value(value: JsValue) -> Result<Self, Self::Error>;
+}

src/lib.rs

@@ -18,7 +18,7 @@ use core::ops::{
 };
 use core::u32;
 
-use crate::convert::{FromWasmAbi, WasmRet, WasmSlice};
+use crate::convert::{FromWasmAbi, TryFromJsValue, WasmRet, WasmSlice};
 
 macro_rules! if_std {
     ($($i:item)*) => ($(
@@ -815,6 +815,17 @@ if_std! {
             }
         }
     }
+
+    impl TryFromJsValue for String {
+        type Error = JsValue;
+
+        fn try_from_js_value(value: JsValue) -> Result<Self, Self::Error> {
+            match value.as_string() {
+                Some(s) => Ok(s),
+                None => Err(value),
+            }
+        }
+    }
 }
 
 impl From<bool> for JsValue {