Fix invalid allocation_size code generation when dealing with empty records

bindgen/src/bindings/cpp/templates/rec.cpp

@@ -33,7 +33,11 @@ void {{ ffi_converter_name }}::write(RustStream &stream, const {{ class_name }}
 }
 
 int32_t {{ ffi_converter_name }}::allocation_size(const {{ class_name }} &val) {
+    {% if rec.fields().is_empty() %}
+    return 0;
+    {% else %}
     return {% for field in rec.fields() %}
         {{ field|allocation_size_fn}}(val.{{ field.name()|var_name() }}){% if !loop.last %} +{% else -%};{%- endif %}
     {%- endfor %}
-}
+    {% endif %}
+}

cpp-tests/CMakeLists.txt

@@ -87,6 +87,7 @@ test_case(uniffi_docstring)
 test_case(trait_methods)
 test_case(custom_types_builtin)
 test_case(enum_style_test)
+test_case(empty_type)
 
 scaffolding_test_case(arithmetic)
 scaffolding_test_case(callbacks)
@@ -101,6 +102,7 @@ scaffolding_test_case(traits)
 scaffolding_test_case(coverall)
 scaffolding_test_case(custom_types_builtin)
 scaffolding_test_case(enum_style_test)
+scaffolding_test_case(empty_type)
 
 add_library(uniffi_fixtures SHARED
     ${SCAFFOLDING_LIB_FILES})

cpp-tests/scaffolding_tests/empty_type/lib_empty_type.cpp

@@ -0,0 +1,9 @@
+#include <lib_empty_type.hpp>
+
+empty_type::Empty empty_type::get_empty_type() {
+    return Empty {};
+}
+
+void empty_type::send_empty_type(Empty e) {}
+
+#include <empty_type_cpp_scaffolding.cpp>

cpp-tests/scaffolding_tests/empty_type/lib_empty_type.hpp

@@ -0,0 +1,11 @@
+#include <cstdint>
+
+namespace {
+    namespace empty_type {
+        struct Empty {};
+
+        Empty get_empty_type();
+
+        void send_empty_type(Empty e);
+    }
+}

cpp-tests/tests/empty_type/main.cpp

@@ -0,0 +1,11 @@
+#include "test_common.hpp"
+
+#include <empty_type.hpp>
+
+int main() {
+    auto empty = empty_type::get_empty_type();
+
+    empty_type::send_empty_type(empty);
+
+    return 0;
+}

fixtures/Cargo.toml

@@ -22,3 +22,4 @@ uniffi-fixture-time = { git = "https://github.com/NordSecurity/uniffi-rs.git", t
 uniffi-fixture-trait-methods = { git = "https://github.com/NordSecurity/uniffi-rs.git", tag = "v0.3.1+v0.25.0" }
 uniffi-custom-types-builtin = { path = "custom-types-builtin" }
 uniffi-enum-style-test = { path = "enum-style-test" }
+uniffi-empty-type = { path = "empty-type" }

fixtures/empty-type/Cargo.toml

@@ -0,0 +1,14 @@
+[package]
+name = "uniffi-empty-type"
+version = "0.1.0"
+edition = "2021"
+
+[lib]
+crate-type = ["lib", "cdylib"]
+name = "uniffi_empty_type"
+
+[dependencies]
+uniffi = { workspace = true }
+
+[build-dependencies]
+uniffi = { workspace = true, features = ["build"] }

fixtures/empty-type/build.rs

@@ -0,0 +1,3 @@
+fn main() {
+    uniffi::generate_scaffolding("src/empty_type.udl").unwrap();
+}

fixtures/empty-type/src/empty_type.udl

@@ -0,0 +1,6 @@
+dictionary Empty {};
+
+namespace empty_type{
+    Empty get_empty_type();
+    void send_empty_type(Empty e);
+};

fixtures/empty-type/src/lib.rs

@@ -0,0 +1,9 @@
+pub struct Empty {}
+
+pub fn get_empty_type() -> Empty {
+    Empty {}
+}
+
+pub fn send_empty_type(empty: Empty) {}
+
+uniffi::include_scaffolding!("empty_type");

fixtures/src/lib.rs

@@ -15,4 +15,5 @@ mod uniffi_fixtures {
 
     uniffi_cpp_custom_types_builtin::uniffi_reexport_scaffolding!();
     uniffi_enum_style_test::uniffi_reexport_scaffolding!();
+    uniffi_empty_type::uniffi_reexport_scaffolding!();
 }