fix from_unmanaged not being implemented for C++ types, and add corre…

…sponding test

gen/src/write.rs

@@ -1776,6 +1776,18 @@ fn write_shared_ptr(out: &mut OutFile, key: NamedImplKey) {
         writeln!(out, "}}");
     }
     begin_function_definition(out);
+    writeln!(
+        out,
+        "void cxxbridge1$shared_ptr${}$from_unmanaged(::std::shared_ptr<{}>* ptr, void* data) noexcept {{",
+        instance, inner,
+    );
+    writeln!(
+        out,
+        "new (ptr) std::shared_ptr<{}>(static_cast<{}*>(data));",
+        inner, inner
+    );
+    writeln!(out, "}}");
+    begin_function_definition(out);
     writeln!(
         out,
         "void cxxbridge1$shared_ptr${}$clone(const ::std::shared_ptr<{}>& self, ::std::shared_ptr<{}> *ptr) noexcept {{",

tests/test.rs

@@ -281,14 +281,22 @@ fn test_shared_ptr_weak_ptr() {
 }
 
 #[test]
-fn test_unique_to_shared_ptr() {
+fn test_unique_to_shared_ptr_string() {
     let unique = ffi::c_return_unique_ptr_string();
     let ptr = &*unique as *const _;
     let shared = unique.to_shared();
     assert_eq!(&*shared as *const _, ptr);
     assert_eq!(&*shared, "2020");
 }
 
+#[test]
+fn test_unique_to_shared_ptr_cpp_type() {
+    let unique = ffi::c_return_unique_ptr();
+    let ptr = &*unique as *const _;
+    let shared = unique.to_shared();
+    assert_eq!(&*shared as *const _, ptr);
+}
+
 #[test]
 fn test_c_ns_method_calls() {
     let unique_ptr = ffi2::ns_c_return_unique_ptr_ns();