Python: Fix class hierarchy generated for traits. Fixes mozilla#2264.

CHANGELOG.md

@@ -16,6 +16,7 @@
 
 - `uniffi.toml` of crates without a `lib` type where ignored in 0.28.1
 - Python: Fixed a bug when enum/error names were not proper camel case (HTMLError instead of HtmlError).
+- Python: Fixed the class hierarcy generated for traits ((#2264)[https://github.com/mozilla/uniffi-rs/issues/2264])
 
 [All changes in [[UnreleasedUniFFIVersion]]](https://github.com/mozilla/uniffi-rs/compare/v0.28.1...HEAD).
 

fixtures/proc-macro/tests/bindings/test_proc_macro.py

@@ -3,6 +3,7 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 from proc_macro import *
+from proc_macro import TraitWithForeignImpl
 
 one = make_one(123)
 assert one.inner == 123
@@ -25,11 +26,14 @@
 assert(rename_test())
 
 trait_impl = obj.get_trait(None)
+assert isinstance(trait_impl, Trait)
 assert trait_impl.concat_strings("foo", "bar") == "foobar"
 assert obj.get_trait(trait_impl).concat_strings("foo", "bar") == "foobar"
 assert concat_strings_by_ref(trait_impl, "foo", "bar") == "foobar"
 
 trait_impl2 = obj.get_trait_with_foreign(None)
+# This is an instance of `TraitWithForeignImpl` - `TraitWithForeign` is used primarily for subclassing.
+assert isinstance(trait_impl2, TraitWithForeignImpl)
 assert trait_impl2.name() == "RustTraitImpl"
 assert obj.get_trait_with_foreign(trait_impl2).name() == "RustTraitImpl"
 

uniffi_bindgen/src/bindings/python/gen_python/mod.rs

@@ -423,24 +423,6 @@ impl PythonCodeOracle {
             None => "0".to_owned(),
         }
     }
-
-    /// Get the name of the protocol and class name for an object.
-    ///
-    /// If we support callback interfaces, the protocol name is the object name, and the class name is derived from that.
-    /// Otherwise, the class name is the object name and the protocol name is derived from that.
-    ///
-    /// This split determines what types `FfiConverter.lower()` inputs.  If we support callback
-    /// interfaces, `lower` must lower anything that implements the protocol.  If not, then lower
-    /// only lowers the concrete class.
-    fn object_names(&self, obj: &Object) -> (String, String) {
-        let class_name = self.class_name(obj.name());
-        if obj.has_callback_interface() {
-            let impl_name = format!("{class_name}Impl");
-            (class_name, impl_name)
-        } else {
-            (format!("{class_name}Protocol"), class_name)
-        }
-    }
 }
 
 impl VisitMut for PythonCodeOracle {
@@ -659,11 +641,6 @@ pub mod filters {
         Ok(PythonCodeOracle.ffi_struct_name(nm))
     }
 
-    /// Get the idiomatic Python rendering of an individual enum variant.
-    pub fn object_names(obj: &Object) -> Result<(String, String), askama::Error> {
-        Ok(PythonCodeOracle.object_names(obj))
-    }
-
     /// Get the idiomatic Python rendering of docstring
     pub fn docstring(docstring: &str, spaces: &i32) -> Result<String, askama::Error> {
         let docstring = textwrap::dedent(docstring);

uniffi_bindgen/src/bindings/python/templates/CallbackInterfaceTemplate.py

@@ -1,6 +1,7 @@
 {%- let cbi = ci|get_callback_interface_definition(name) %}
 {%- let ffi_init_callback = cbi.ffi_init_callback() %}
 {%- let protocol_name = type_name.clone() %}
+{%- let protocol_base_class = "typing.Protocol" %}
 {%- let protocol_docstring = cbi.docstring() %}
 {%- let vtable = cbi.vtable() %}
 {%- let methods = cbi.methods() %}

uniffi_bindgen/src/bindings/python/templates/ObjectTemplate.py

@@ -1,11 +1,28 @@
 {%- let obj = ci|get_object_definition(name) %}
-{%- let (protocol_name, impl_name) = obj|object_names %}
 {%- let methods = obj.methods() %}
+{%- let protocol_name = format!("{type_name}Protocol") %}
 {%- let protocol_docstring = obj.docstring() %}
+{%- let protocol_base_class = "typing.Protocol" %}
+{%- include "Protocol.py" %}
 
-{% include "Protocol.py" %}
+{%- let impl_name %}
+{%- if obj.has_callback_interface() %}
+# {{ type_name }} is a foreign trait so treated like a callback interface, where the
+# primary use-case is the trait being implemented locally.
+# It is a base-class local implementations might subclass.
+{# We reuse "Protocol.py" for this, even though here we are not generating a protocol #}
+{%-     let protocol_name = format!("{type_name}") %}
+{%-     let protocol_base_class = "" %}
+{%      include "Protocol.py" %}
+
+{%-     let impl_name = format!("{type_name}Impl") %}
+# `{{ impl_name }}` is the implementation for a Rust implemented version.
+{%- else %}
+# {{ type_name }} is a Rust-only trait - it's a wrapper around a Rust implementation.
+{%-     let impl_name = type_name.clone() %}
+{%- endif %}
 
-{% if ci.is_name_used_as_error(name) %}
+{%- if ci.is_name_used_as_error(name) %}
 class {{ impl_name }}(Exception):
 {%- else %}
 class {{ impl_name }}:

uniffi_bindgen/src/bindings/python/templates/Protocol.py

@@ -1,4 +1,5 @@
-class {{ protocol_name }}(typing.Protocol):
+{# misnamed - a generic "abstract base class". Used as both a protocol and an ABC for traits. #}
+class {{ protocol_name }}({{ protocol_base_class }}):
     {%- call py::docstring_value(protocol_docstring, 4) %}
     {%- for meth in methods.iter() %}
     def {{ meth.name() }}(self, {% call py::arg_list_decl(meth) %}):