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Fix clippy unused_unit warnings in host_bindgen macro for void return functions #658

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Fix clippy unused_unit warnings in host_bindgen macro for void return functions #658

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544f52f
Initial plan for issue
Copilot Jun 23, 2025
95c27d0
Fix clippy unused_unit warnings in host_bindgen macro for void return…
Copilot Jun 23, 2025
412ab9f
Address PR feedback: Add void return test case, simplify clippy logic…
Copilot Jun 23, 2025
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2 changes: 1 addition & 1 deletion src/hyperlight_component_util/src/guest.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,7 @@ fn emit_import_extern_decl<'a, 'b, 'c>(
ResourceItemName::Static(mn) => quote! { #mn },
},
};
// Use unmarshal directly since empty TokenStream generates no code
let decl = quote! {
fn #n(&mut self, #(#param_decls),*) -> #result_decl {
let mut args = ::alloc::vec::Vec::new();
Expand All @@ -78,7 +79,6 @@ fn emit_import_extern_decl<'a, 'b, 'c>(
::hyperlight_common::flatbuffer_wrappers::function_types::ReturnType::VecBytes,
);
let ::core::result::Result::Ok(#ret) = #ret else { panic!("bad return from guest {:?}", #ret) };
#[allow(clippy::unused_unit)]
#unmarshal
}
};
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2 changes: 1 addition & 1 deletion src/hyperlight_component_util/src/hl.rs
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Expand Up @@ -655,7 +655,7 @@ pub fn emit_hl_unmarshal_param(s: &mut State, id: Ident, pt: &Value) -> TokenStr
/// are no names in it (i.e. a unit type)
pub fn emit_hl_unmarshal_result(s: &mut State, id: Ident, rt: &etypes::Result) -> TokenStream {
match rt {
etypes::Result::Named(rs) if rs.is_empty() => quote! { () },
etypes::Result::Named(rs) if rs.is_empty() => TokenStream::new(),
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I don't like this as a solution, because it changes the contract for this helper to something a lot less intuitive:

The resultant token stream will be an expression which typechecks at the Rust type ...

becomes

The resultant token stream will typecheck at the Rust type of the unnamed type of the result, or the empty stream if named results are used

which means that it can't generally be used to uniformly generate a return value. Right now, this expression is only used in the tail position of a function definition, so it works "by coincidence"---but this change makes the interface more brittle (e.g. if you wanted to refactor the macro to trace the return value, you would need special cases to not accidentally generate an empty let statement).

etypes::Result::Unnamed(vt) => {
let toks = emit_hl_unmarshal_value(s, id, vt);
quote! { { #toks }.0 }
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8 changes: 4 additions & 4 deletions src/tests/rust_guests/witguest/Cargo.lock
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2 changes: 2 additions & 0 deletions src/tests/rust_guests/witguest/guest.wit
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Expand Up @@ -53,6 +53,8 @@ interface roundtrip {
enum-a, enum-b, enum-c
}
roundtrip-enum: func(x: testenum) -> testenum;
// Test case for void return function (no clippy unused_unit warnings)
do-something: func(number: u32);
}

interface host-resource {
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3 changes: 3 additions & 0 deletions src/tests/rust_guests/witguest/src/main.rs
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Expand Up @@ -113,6 +113,9 @@ impl test::wit::Roundtrip for Guest {
) -> test::wit::roundtrip::Testenum {
(Host {}).roundtrip_enum(x)
}
fn do_something(&mut self, number: u32) {
(Host {}).do_something(number)
}
}

impl test::wit::TestHostResource for Guest {
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