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fix: host_bindgen! returns Result instead of panicking on guest errors #1317

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fix: host_bindgen! returns Result instead of panicking on guest errors #1317

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2 changes: 2 additions & 0 deletions src/hyperlight_component_util/src/emit.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -124,6 +124,7 @@ pub struct Mod {
pub items: TokenStream,
pub traits: BTreeMap<Ident, Trait>,
pub impls: BTreeMap<(Vec<Ident>, Ident), TokenStream>,
pub emitted_type_names: BTreeSet<Ident>,

@syntactically syntactically Jun 25, 2026

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I don't follow what this is being used for?

}
impl Mod {
pub fn empty() -> Self {
Expand All @@ -132,6 +133,7 @@ impl Mod {
items: TokenStream::new(),
traits: BTreeMap::new(),
impls: BTreeMap::new(),
emitted_type_names: BTreeSet::new(),
}
}
/// Get a reference to a sub-module, creating it if necessary
Expand Down
7 changes: 4 additions & 3 deletions src/hyperlight_component_util/src/host.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,7 @@ fn emit_export_extern_decl<'a, 'b, 'c>(
.map(|p| rtypes::emit_func_param(s, p))
.collect::<Vec<_>>();
let result_decl = rtypes::emit_func_result(s, &ft.result);
let result_decl = quote! { ::std::result::Result<#result_decl, ::hyperlight_host::error::HyperlightError> };
let hln = emit_fn_hl_name(s, ed.kebab_name);
let ret = format_ident!("ret");
let marshal = ft
Expand All @@ -66,11 +67,11 @@ fn emit_export_extern_decl<'a, 'b, 'c>(
#hln,
marshalled,
);
let ::std::result::Result::Ok(#ret) = #ret else { panic!("bad return from guest {:?}", #ret) };
let #ret = #ret?;
#[allow(clippy::unused_unit)]
let mut rts = self.rt.lock().unwrap();

@danbugs danbugs Jun 25, 2026

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This will still panic--fine?

#[allow(clippy::unused_unit)]
#unmarshal
Ok(#unmarshal)
}
}
}
Expand Down Expand Up @@ -121,7 +122,7 @@ fn emit_export_instance<'a, 'b, 'c>(s: &'c mut State<'a, 'b>, wn: WitName, it: &

let ns = wn.namespace_path();
let nsi = wn.namespace_idents();
let trait_name = kebab_to_type(wn.name);
let trait_name = kebab_to_exports_name(wn.name);
let r#trait = s.r#trait(&nsi, trait_name.clone());
let tvs = r#trait
.tvs
Expand Down
2 changes: 1 addition & 1 deletion src/hyperlight_component_util/src/resource.rs
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Expand Up @@ -99,7 +99,7 @@ pub fn emit_tables<'a, 'b, 'c>(
#sphantom
}
impl<I: #bound #sv> #rtsid<I #svs> {
fn new() -> Self {
pub(crate) fn new() -> Self {
#rtsid {
#(#inits,)*
_phantomI: ::core::marker::PhantomData,
Expand Down
38 changes: 34 additions & 4 deletions src/hyperlight_component_util/src/rtypes.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -641,6 +641,11 @@ fn emit_extern_decl<'a, 'b, 'c>(
.map(|p| emit_func_param(&mut s, p))
.collect::<Vec<_>>();
let result = emit_func_result(&mut s, &ft.result);
let result = if !s.is_guest && s.is_export {
quote! { ::std::result::Result<#result, ::hyperlight_host::error::HyperlightError> }
} else {
result
};
Comment on lines +644 to +648

@danbugs danbugs Jun 25, 2026

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Might want a helper for this? It seems to repeat enough times.

@syntactically syntactically Jun 25, 2026

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I think it should be pushed into emit_func_result, whose semantic job is to centralize the logic for converting a C-M result type into a Rust type for bindings generation.

Are there any times where we use that where we don't want it?

quote! {
fn #n(&mut self, #(#params),*) -> #result;
}
Expand All @@ -663,12 +668,22 @@ fn emit_extern_decl<'a, 'b, 'c>(
}
ResourceItemName::Method(n) => {
let result = emit_func_result(&mut sv, &ft.result);
let result = if !sv.is_guest && sv.is_export {
quote! { ::std::result::Result<#result, ::hyperlight_host::error::HyperlightError> }
} else {
result
};
sv.cur_trait().items.extend(quote! {
fn #n(&mut self, #(#params),*) -> #result;
});
}
ResourceItemName::Static(n) => {
let result = emit_func_result(&mut sv, &ft.result);
let result = if !sv.is_guest && sv.is_export {
quote! { ::std::result::Result<#result, ::hyperlight_host::error::HyperlightError> }
} else {
result
};
sv.cur_trait().items.extend(quote! {
fn #n(&mut self, #(#params),*) -> #result;
});
Expand All @@ -691,6 +706,9 @@ fn emit_extern_decl<'a, 'b, 'c>(
) -> TokenStream {
let id = kebab_to_type(ed.kebab_name);
let mut s = s.helper();
if !s.cur_mod().emitted_type_names.insert(id.clone()) {

@syntactically syntactically Jun 25, 2026

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What is this being used for? It seems like it will simply drop some definitions, which doesn't seem ideal?

return TokenStream::new();
}

let t = emit_defined(&mut s, v, id, t);
s.cur_mod().items.extend(t);
Expand All @@ -712,6 +730,9 @@ fn emit_extern_decl<'a, 'b, 'c>(
let rn = kebab_to_type(ed.kebab_name);
s.add_helper_supertrait(rn.clone());
let mut s = s.helper();
if !s.cur_mod().emitted_type_names.insert(rn.clone()) {
return quote! {};
}
s.cur_trait = Some(rn.clone());
s.cur_trait().items.extend(quote! {
type T: ::core::marker::Send;
Expand All @@ -729,7 +750,12 @@ fn emit_extern_decl<'a, 'b, 'c>(
emit_instance(&mut s, wn.clone(), it);

let nsids = wn.namespace_idents();
let repr = s.r#trait(&nsids, kebab_to_type(wn.name));
let trait_name = if !s.is_guest && s.is_export {
kebab_to_exports_name(wn.name)
} else {
kebab_to_type(wn.name)
};
let repr = s.r#trait(&nsids, trait_name.clone());
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let vs = if !repr.tvs.is_empty() {
let vs = repr.tvs.clone();
let tvs = vs
Expand All @@ -745,9 +771,9 @@ fn emit_extern_decl<'a, 'b, 'c>(
let tns = wn.namespace_path();
let tn = kebab_to_type(wn.name);
let trait_bound = if tns.is_empty() {
quote! { #rp #tn }
quote! { #rp #trait_name }
} else {
quote! { #rp #tns::#tn }
quote! { #rp #tns::#trait_name }
};
quote! {
type #tn: #trait_bound #vs;
Expand All @@ -766,7 +792,11 @@ fn emit_instance<'a, 'b, 'c>(s: &'c mut State<'a, 'b>, wn: WitName, it: &'c Inst
tracing::debug!("emitting instance {:?}", wn);
let mut s = s.with_cursor(wn.namespace_idents());

let name = kebab_to_type(wn.name);
let name = if !s.is_guest && s.is_export {
kebab_to_exports_name(wn.name)
} else {
kebab_to_type(wn.name)
};

s.cur_helper_mod = Some(kebab_to_namespace(wn.name));
s.cur_trait = Some(name.clone());
Expand Down
29 changes: 21 additions & 8 deletions src/hyperlight_host/tests/wit_test.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -293,9 +293,12 @@ fn sb() -> TestSandbox<Host, MultiUseSandbox> {

mod wit_test {

use hyperlight_host::error::HyperlightError;
use proptest::prelude::*;

use crate::bindings::test::wit::{Roundtrip, TestExports, TestHostResource, roundtrip};
use crate::bindings::test::wit::{
FailableExports, RoundtripExports, TestExports, TestHostResourceExports, roundtrip,
};
use crate::sb;

prop_compose! {
Expand Down Expand Up @@ -347,7 +350,7 @@ mod wit_test {
proptest! {
#[test]
fn $fn(x $($ty)*) {
assert_eq!(x, sb().roundtrip().$fn(x.clone()))
assert_eq!(x, sb().roundtrip().$fn(x.clone()).unwrap())
}
}
}
Expand Down Expand Up @@ -394,7 +397,7 @@ mod wit_test {

#[test]
fn test_roundtrip_no_result() {
sb().roundtrip().roundtrip_no_result(42);
sb().roundtrip().roundtrip_no_result(42).unwrap();
}

use std::sync::atomic::Ordering::Relaxed;
Expand All @@ -404,7 +407,7 @@ mod wit_test {
let guard = crate::SERIALIZE_TEST_RESOURCE_TESTS.lock();
crate::HAS_BEEN_DROPPED.store(false, Relaxed);
{
sb().test_host_resource().test_uses_locally();
sb().test_host_resource().test_uses_locally().unwrap();
}
assert!(crate::HAS_BEEN_DROPPED.load(Relaxed));
drop(guard);
Expand All @@ -416,14 +419,24 @@ mod wit_test {
{
let mut sb = sb();
let inst = sb.test_host_resource();
let r = inst.test_makes();
inst.test_accepts_borrow(&r);
inst.test_accepts_own(r);
inst.test_returns();
let r = inst.test_makes().unwrap();
inst.test_accepts_borrow(&r).unwrap();
inst.test_accepts_own(r).unwrap();
inst.test_returns().unwrap();
}
assert!(crate::HAS_BEEN_DROPPED.load(Relaxed));
drop(guard);
}

#[test]
fn test_guest_call_error_returns_error() {
let mut sb = sb();
let err = sb.failable().guest_panic().unwrap_err();
assert!(matches!(
err,
HyperlightError::GuestAborted(_, msg) if msg.contains("deliberate guest panic")
));
}
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}

mod pick_world_bindings {
Expand Down
5 changes: 5 additions & 0 deletions src/tests/rust_guests/witguest/guest.wit
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@ world test {
import host-resource;
export roundtrip;
export test-host-resource;
export failable;
}

interface roundtrip {
Expand Down Expand Up @@ -89,4 +90,8 @@ interface test-host-resource {
test-accepts-borrow: func(x: borrow<testresource>);
test-accepts-own: func(x: own<testresource>);
test-returns: func() -> own<testresource>;
}

interface failable {
guest-panic: func() -> string;
}
10 changes: 10 additions & 0 deletions src/tests/rust_guests/witguest/src/main.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -166,6 +166,12 @@ impl test::wit::Roundtrip for Guest {
}
}

impl test::wit::Failable for Guest {
fn guest_panic(&mut self) -> alloc::string::String {
panic!("deliberate guest panic")
}
}

use alloc::string::ToString;

use test::wit::host_resource::Testresource;
Expand Down Expand Up @@ -214,6 +220,10 @@ impl test::wit::TestExports<Host> for Guest {
fn test_host_resource(&mut self) -> &mut Self {
self
}
type Failable = Self;
fn failable(&mut self) -> &mut Self {
self
}
}

static GUEST_STATE: Mutex<Guest> = Mutex::new(Guest {
Expand Down
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