From 0d075831a8d215651d85e4eeb7c5ccf02e17b854 Mon Sep 17 00:00:00 2001
From: Jules Bertholet <jules.bertholet@gmail.com>
Date: Mon, 9 Aug 2021 16:20:19 +0200
Subject: [PATCH] Remmove panic by adding `Default` bound

---
 Cargo.toml            |  3 ++-
 src/convert/slices.rs | 15 ++++++++-------
 2 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index 828dd99b466..df0fe064e11 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -22,7 +22,7 @@ test = false
 [features]
 default = ["spans", "std"]
 spans = ["wasm-bindgen-macro/spans"]
-std = []
+std = ["array-init"]
 serde-serialize = ["serde", "serde_json", "std"]
 nightly = []
 enable-interning = ["std"]
@@ -40,6 +40,7 @@ wasm-bindgen-macro = { path = "crates/macro", version = "=0.2.75" }
 serde = { version = "1.0", optional = true }
 serde_json = { version = "1.0", optional = true }
 cfg-if = "1.0.0"
+array-init = { version = "2.0.0", optional = true }
 
 [target.'cfg(target_arch = "wasm32")'.dev-dependencies]
 js-sys = { path = 'crates/js-sys', version = '0.3.52' }
diff --git a/src/convert/slices.rs b/src/convert/slices.rs
index 5286685882e..a0c08602755 100644
--- a/src/convert/slices.rs
+++ b/src/convert/slices.rs
@@ -146,7 +146,7 @@ cfg_if! {
 }
 
 if_std! {
-    use std::convert::TryFrom;
+    use std::{hint, iter};
 
     impl<T> IntoWasmAbi for Vec<T> where Box<[T]>: IntoWasmAbi<Abi = WasmSlice> {
         type Abi = <Box<[T]> as IntoWasmAbi>::Abi;
@@ -190,20 +190,21 @@ if_std! {
         fn none() -> WasmSlice { null_slice() }
     }
 
-    impl<T, const N: usize> FromWasmAbi for [T; N] where Box<[T]>: FromWasmAbi<Abi = WasmSlice> {
+    impl<T: Default, const N: usize> FromWasmAbi for [T; N] where Box<[T]>: FromWasmAbi<Abi = WasmSlice> {
         type Abi = <Box<[T]> as FromWasmAbi>::Abi;
 
         #[inline]
         unsafe fn from_abi(js: Self::Abi) -> Self {
-            let result = <[T; N]>::try_from(<Vec<T>>::from(<Box<[T]>>::from_abi(js)));
-            return match result {
-                Ok(arr) => arr,
-                Err(_) => panic!("JS array length does not match Rust array")
+            let vec = <Vec<T>>::from(<Box<[T]>>::from_abi(js));
+            let iter = vec.into_iter().chain(iter::repeat_with(T::default));
+            match array_init::from_iter(iter) {
+                Some(arr) => arr,
+                None => hint::unreachable_unchecked(),
             }
         }
     }
 
-    impl<T, const N: usize> OptionFromWasmAbi for [T; N] where Box<[T]>: FromWasmAbi<Abi = WasmSlice> {
+    impl<T: Default, const N: usize> OptionFromWasmAbi for [T; N] where Box<[T]>: FromWasmAbi<Abi = WasmSlice> {
         #[inline]
         fn is_none(abi: &WasmSlice) -> bool { abi.ptr == 0 }
     }