c++/feature: make possible to return Option<&ForeignClass>

may be it is possible to simplify code after
resolving rust-lang/rust#48869

Author: Dushistov

c++_tests/c++/main.cpp

@@ -353,8 +353,20 @@ TEST(TestOptional, smokeTest)
         ASSERT_FALSE(!!val2);
     }
 
-    EXPECT_NEAR(10., x.f4({5.}), std::numeric_limits<double>::epsilon());
+    EXPECT_NEAR(10., x.f4({ 5. }), std::numeric_limits<double>::epsilon());
     EXPECT_NEAR(-1., x.f4({}), std::numeric_limits<double>::epsilon());
+
+    {
+        auto val = x.f5(true);
+        ASSERT_TRUE(!!val);
+        FooRef foo = std::move(*val);
+        EXPECT_EQ(5, foo.f(0, 0));
+        EXPECT_EQ(std::string("aaa"), foo.getName().to_std_string());
+    }
+    {
+        auto foo = x.f5(false);
+        EXPECT_FALSE(!!foo);
+    }
 }
 
 TEST(TestResult, smokeTest)

c++_tests/src/lib.rs.in

@@ -365,9 +365,17 @@ foreigner_class!(class TestPassPathAsParam {
     method TestPassPathAsParam::path(&self) -> &str;
 });
 
-#[derive(Default)]
-pub struct TestOptional {}
+pub struct TestOptional {
+    foo: Foo,
+}
 
+impl Default for TestOptional {
+    fn default() -> TestOptional {
+        TestOptional {
+            foo: Foo::new(5, "aaa"),
+        }
+    }
+}
 impl TestOptional {
     fn f1(&self, ret_notnull: bool) -> Option<Foo> {
         if ret_notnull {
@@ -395,6 +403,13 @@ impl TestOptional {
     fn f4(&self, a: Option<f64>) -> f64 {
         a.map(|v| v * 2.).unwrap_or(-1.)
     }
+    fn f5(&self, x: bool) -> Option<&Foo> {
+        if x {
+            Some(&self.foo)
+        } else {
+            None
+        }
+    }
 }
 
 foreigner_class!(class TestOptional {
@@ -404,6 +419,7 @@ foreigner_class!(class TestOptional {
     method TestOptional::f2(&self, ret_notnull: bool) -> Option<f64>;
     method TestOptional::f3(&self, ret_notnull: bool) -> Option<u32>;
     method TestOptional::f4(&self, _: Option<f64>) -> f64;
+    method TestOptional::f5(&self, x: bool) -> Option<&Foo>;
 });
 
 #[derive(Default)]

macroslib/src/cpp/map_type.rs

@@ -8,7 +8,8 @@ use petgraph::Direction;
 use my_ast::{code_to_item, if_option_return_some_type, if_result_return_ok_err_types,
              if_vec_return_elem_type, normalized_ty_string, parse_ty, RustType};
 use errors::fatal_error;
-use types_conv_map::{ForeignTypeInfo, FROM_VAR_TEMPLATE};
+use types_conv_map::{make_unique_rust_typename, ForeignTypeInfo, FROM_VAR_TEMPLATE,
+                     TO_VAR_TEMPLATE};
 use {CppConfig, CppOptional, CppVariant, ForeignEnumInfo, ForeignerClassInfo, TypesConvMap};
 use cpp::{CppConverter, CppForeignTypeInfo};
 use cpp::cpp_code::c_class_type;
@@ -571,6 +572,86 @@ fn handle_option_type_in_result<'a>(
             }),
         }));
     }
+
+    //handle Option<&ForeignClass> case
+    if let ast::TyKind::Rptr(
+        _,
+        ast::MutTy {
+            ty: ref under_ref_ty,
+            mutbl: ast::Mutability::Immutable,
+        },
+    ) = opt_ty.node
+    {
+        if let Some(fclass) = conv_map
+            .find_foreigner_class_with_such_self_type(under_ref_ty, false)
+            .map(|v| v.clone())
+        {
+            let foreign_info =
+                foreign_class_foreign_name(sess, conv_map, &fclass, under_ref_ty.span, false)?;
+            let this_type_for_method = fclass.this_type_for_method.as_ref().ok_or_else(|| {
+                fatal_error(
+                    sess,
+                    fclass.span,
+                    &format!(
+                        "Class {} (namespace {}) return as reference, but there is no constructor",
+                        fclass.name, cpp_cfg.namespace_name,
+                    ),
+                )
+            })?;
+            let this_type: RustType = this_type_for_method.clone().into();
+            let void_ptr_typename = Symbol::intern("*mut ::std::os::raw::c_void");
+            let my_void_ptr_ti = RustType::new(
+                parse_ty(sess, DUMMY_SP, void_ptr_typename)?,
+                make_unique_rust_typename(void_ptr_typename, this_type.normalized_name),
+            );
+            let arg_rust_ty: RustType = arg_ty.clone().into();
+            conv_map.add_type(arg_rust_ty.clone());
+            conv_map.add_conversation_rule(
+                arg_rust_ty,
+                my_void_ptr_ti,
+                Symbol::intern(&format!(
+                    r#"
+    let {to_var}: *mut ::std::os::raw::c_void = match {from_var} {{
+        Some(x) => x as *const {self_type} as *mut ::std::os::raw::c_void,
+        None => ::std::ptr::null_mut(),
+    }};
+"#,
+                    to_var = TO_VAR_TEMPLATE,
+                    from_var = FROM_VAR_TEMPLATE,
+                    self_type = this_type.normalized_name,
+                )).into(),
+            );
+
+            let (typename, output_converter) = match cpp_cfg.cpp_optional {
+                CppOptional::Std17 => (
+                    Symbol::intern(&format!("std::optional<{}Ref>", fclass.name)),
+                    format!(
+                        "{var} != nullptr ? {Type}Ref({var}) : std::optional<{Type}Ref>()",
+                        Type = fclass.name,
+                        var = FROM_VAR_TEMPLATE,
+                    ),
+                ),
+                CppOptional::Boost => (
+                    Symbol::intern(&format!("boost::optional<{}Ref>", fclass.name)),
+                    format!(
+                        "{var} != nullptr ? {Type}Ref({var}) : boost::optional<{Type}Ref>()",
+                        Type = fclass.name,
+                        var = FROM_VAR_TEMPLATE,
+                    ),
+                ),
+            };
+            return Ok(Some(CppForeignTypeInfo {
+                base: foreign_info,
+                c_converter: String::new(),
+                cpp_converter: Some(CppConverter {
+                    typename,
+                    output_converter,
+                    input_converter: "#error".to_string(),
+                }),
+            }));
+        }
+    }
+
     let mut cpp_info_opt = map_ordinal_result_type(sess, conv_map, arg_ty)?;
     let cpp_info_ty = map_ordinal_result_type(sess, conv_map, opt_ty)?;
     let f_opt_ty = cpp_info_ty.base.name;

macroslib/src/types_conv_map/mod.rs

@@ -780,7 +780,7 @@ impl TypesConvMap {
         debug!("TypesConvMap::add_conversation_rule {} -> {}", from, to);
         let from = get_graph_node(&mut self.conv_graph, &mut self.rust_names_map, from);
         let to = get_graph_node(&mut self.conv_graph, &mut self.rust_names_map, to);
-        self.conv_graph.add_edge(from, to, rule);
+        self.conv_graph.update_edge(from, to, rule);
     }
 
     pub(crate) fn register_exported_enum(&mut self, enum_info: &ForeignEnumInfo) {

macroslib/tests/test_complex_cases.rs

@@ -651,6 +651,7 @@ foreigner_class!(class Foo {
    method Foo::f2(&self) -> Option<f64>;
    method Foo::f3(&self) -> Option<u32>;
    method Foo::f4(&self) -> Option<usize>;
+   method Foo::f5(&self) -> Option<&Boo>;
 });
 "#,
         &[ForeignLang::Cpp],
@@ -681,6 +682,11 @@ foreigner_class!(class Foo {
             .foreign_code
             .contains("std::optional<uintptr_t> f4()")
     );
+    assert!(
+        cpp_code_pair
+            .foreign_code
+            .contains("std::optional<BooRef> f5()")
+    );
 }
 
 #[test]