Fix several issues dealing with the error interface

bindgen/src/gen_go/mod.rs

@@ -370,7 +370,7 @@ impl GoCodeOracle {
 pub mod filters {
     use super::*;
 
-    fn oracle() -> &'static GoCodeOracle {
+    pub fn oracle() -> &'static GoCodeOracle {
         &GoCodeOracle
     }
 
@@ -575,4 +575,12 @@ impl<'a> TypeRenderer<'a> {
     pub fn cgo_callback_fn(&self, name: &str, module_path: &str) -> String {
         format!("{module_path}_cgo_{name}")
     }
+
+    pub fn field_type_name(&self, field: &Field) -> String {
+        let name = filters::oracle().find(&field.as_type()).type_label();
+        match self.ci.is_name_used_as_error(&name) {
+            true => format!("*{name}"),
+            false => name.to_string(),
+        }
+    }
 }

bindgen/templates/ErrorTemplate.go

@@ -30,7 +30,7 @@ type {{ variant_class_name }} struct {
 	message string
 	{%- else %}
 	{%- for field in variant.fields() %}
-	{{ field.name()|error_field_name }} {{ field|type_name}}
+	{{ field.name()|error_field_name }} {{ self.field_type_name(field) }}
 	{%- endfor %}
 	{%- endif %}
 }
@@ -39,7 +39,7 @@ type {{ variant_class_name }} struct {
 func New{{ variant_class_name }}(
 	{%- if !e.is_flat() %}
 	{%- for field in variant.fields() %}
-	{{ field.name()|var_name }} {{ field|type_name}},
+	{{ field.name()|var_name }} {{ self.field_type_name(field) }},
 	{%- endfor %}
 	{%- endif %}
 ) *{{ type_name.clone() }} {
@@ -81,14 +81,14 @@ type {{ e|ffi_converter_name }} struct{}
 var {{ e|ffi_converter_name }}INSTANCE = {{ e|ffi_converter_name }}{}
 
 func (c {{ e|ffi_converter_name }}) Lift(eb RustBufferI) error {
-	return LiftFromRustBuffer[error](c, eb)
+	return LiftFromRustBuffer[*{{ type_name|class_name }}](c, eb)
 }
 
 func (c {{ e|ffi_converter_name }}) Lower(value *{{ type_name|class_name }}) RustBuffer {
 	return LowerIntoRustBuffer[*{{ type_name|class_name }}](c, value)
 }
 
-func (c {{ e|ffi_converter_name }}) Read(reader io.Reader) error {
+func (c {{ e|ffi_converter_name }}) Read(reader io.Reader) *{{ type_name|class_name }} {
 	errorID := readUint32(reader)
 
 	{%- if e.is_flat() %}

binding_tests/errors_test.go

@@ -151,3 +151,13 @@ func TestErrorNamedError(t *testing.T) {
 	assert.ErrorAs(t, err, &expectedError)
 	assert.Equal(t, "it's an error", expectedError.Unwrap().(*errors.ErrorNamedErrorError).Error_)
 }
+
+func TestNestedError(t *testing.T) {
+	assert.Equal(t, nil, errors.TryNested(false))
+	err := errors.TryNested(true)
+	var expectedError *errors.NestedError
+	assert.ErrorAs(t, err, &expectedError)
+	var expectedNestedError *errors.NestedErrorNested
+	assert.ErrorAs(t, expectedError.Unwrap(), &expectedNestedError)
+	assert.Equal(t, "ValidationError: UnknownError", expectedNestedError.Source.Error())
+}

fixtures/errors/src/errors.udl

@@ -19,6 +19,11 @@ enum BoobyTrapError {
   "HotDoorKnob",
 };
 
+[Error]
+interface NestedError {
+  Nested(ValidationError source);
+};
+
 [Error]
 interface ValidationError {
   InvalidUser(i32 user_id);
@@ -40,6 +45,10 @@ interface ComplexError {
     Option(i32? id_a, i32? id_b);
 };
 
+callback interface Callback {
+    void do_something(BoobyTrapError error);
+};
+
 dictionary Vec2 {
     double x;
     double y;

fixtures/errors/src/lib.rs

@@ -45,6 +45,12 @@ pub enum ComplexError {
     },
 }
 
+#[derive(Debug, thiserror::Error)]
+pub enum NestedError {
+    #[error(transparent)]
+    Nested { source: ValidationError },
+}
+
 #[derive(Debug)]
 pub struct Vec2 {
     x: f64,
@@ -57,6 +63,21 @@ impl Vec2 {
     }
 }
 
+#[uniffi::export]
+fn try_nested(trip: bool) -> Result<(), NestedError> {
+    if trip {
+        Err(NestedError::Nested {
+            source: ValidationError::UnknownError,
+        })
+    } else {
+        Ok(())
+    }
+}
+
+pub trait Callback {
+    fn do_something(&self, error: BoobyTrapError);
+}
+
 fn try_void(trip: bool) -> Result<(), BoobyTrapError> {
     if trip {
         Err(BoobyTrapError::IceSlip)