Revert "Remove feature(alloc_error_handler)"

This reverts commit 5f725871b67de32235d8ac5140f81c32006af237.

substrate/primitives/application-crypto/Cargo.toml

@@ -42,6 +42,7 @@ serde = [ "dep:serde", "scale-info/serde", "sp-core/serde" ]
 # For the regular wasm runtime builds this should not be used.
 full_crypto = [
 	"sp-core/full_crypto",
+	"sp-io/disable_oom",
 	# Don't add `panic_handler` and `alloc_error_handler` since they are expected to be provided
 	# by the user anyway.
 	"sp-io/disable_panic_handler",

substrate/primitives/io/Cargo.toml

@@ -63,10 +63,11 @@ std = [
 with-tracing = [ "sp-tracing/with-tracing" ]
 
 # These two features are used for `no_std` builds for the environments which already provides
-# `#[panic_handler]` and `#[global_allocator]`.
+# `#[panic_handler]`, `#[alloc_error_handler]` and `#[global_allocator]`.
 #
 # For the regular wasm runtime builds those are not used.
 disable_panic_handler = []
+disable_oom = []
 disable_allocator = []
 
 # This feature flag controls the runtime's behavior when encountering
@@ -80,7 +81,8 @@ disable_allocator = []
 # logs, with the caller receving a generic "wasm `unreachable` instruction executed"
 # error message.
 #
-# This has no effect if `disable_panic_handler` enabled.
+# This has no effect if both `disable_panic_handler` and `disable_oom`
+# are enabled.
 #
 # WARNING: Enabling this feature flag requires the `PanicHandler::abort_on_panic`
 #          host function to be supported by the host. Do *not* enable it for your

substrate/primitives/io/src/lib.rs

@@ -75,6 +75,7 @@
 
 #![warn(missing_docs)]
 #![cfg_attr(not(feature = "std"), no_std)]
+#![cfg_attr(enable_alloc_error_handler, feature(alloc_error_handler))]
 
 use sp_std::vec::Vec;
 
@@ -1765,34 +1766,33 @@ mod allocator_impl {
 #[panic_handler]
 #[no_mangle]
 pub fn panic(info: &core::panic::PanicInfo) -> ! {
-	use sp_std::alloc::{alloc::AllocErrorPanicPayload, format, string::String};
-
-	let improved_panic_error_reporting = match () {
-		#[cfg(feature = "improved_panic_error_reporting")]
-		() => true,
-		#[cfg(not(feature = "improved_panic_error_reporting"))]
-		() => false,
-	};
-
-	let message = info
-		.payload()
-		.downcast_ref::<AllocErrorPanicPayload>()
-		.map(|_| {
-			let msg = improved_panic_error_reporting
-				.then_some("Runtime memory exhausted.")
-				.unwrap_or("Runtime memory exhausted. Aborting");
-			String::from(msg)
-		})
-		.unwrap_or_else(|| format!("{info}"));
-
-	if improved_panic_error_reporting {
+	let message = sp_std::alloc::format!("{}", info);
+	#[cfg(feature = "improved_panic_error_reporting")]
+	{
 		panic_handler::abort_on_panic(&message);
-	} else {
+	}
+	#[cfg(not(feature = "improved_panic_error_reporting"))]
+	{
 		logging::log(LogLevel::Error, "runtime", message.as_bytes());
 		core::arch::wasm32::unreachable();
 	}
 }
 
+/// A default OOM handler for WASM environment.
+#[cfg(all(not(feature = "disable_oom"), enable_alloc_error_handler))]
+#[alloc_error_handler]
+pub fn oom(_: core::alloc::Layout) -> ! {
+	#[cfg(feature = "improved_panic_error_reporting")]
+	{
+		panic_handler::abort_on_panic("Runtime memory exhausted.");
+	}
+	#[cfg(not(feature = "improved_panic_error_reporting"))]
+	{
+		logging::log(LogLevel::Error, "runtime", b"Runtime memory exhausted. Aborting");
+		core::arch::wasm32::unreachable();
+	}
+}
+
 /// Type alias for Externalities implementation used in tests.
 #[cfg(feature = "std")]
 pub type TestExternalities = sp_state_machine::TestExternalities<sp_core::Blake2Hasher>;