Generate a __typename handler branch in stubgen. (#500)

* Generate a `__typename` handler branch in stubgen.

* Unset rustflags in tests job, that's for the lints job.

.github/workflows/ci.yml

@@ -179,6 +179,8 @@ jobs:
 
       - name: Install rust + caching
         uses: actions-rust-lang/setup-rust-toolchain@v1
+        with:
+          rustflags: ""
 
       - name: Set up sccache
         uses: mozilla-actions/[email protected]

trustfall_stubgen/src/adapter_creator.rs

@@ -159,6 +159,8 @@ fn emit_property_handling(
     external_imports.insert(parse_import("trustfall::provider::ContextOutcomeIterator"));
     external_imports.insert(parse_import("trustfall::provider::ResolveInfo"));
     external_imports.insert(parse_import("trustfall::FieldValue"));
+    external_imports.insert(parse_import("trustfall::provider::Typename"));
+    external_imports.insert(parse_import("trustfall::provider::resolve_property_with"));
 
     quote! {
         fn resolve_property(
@@ -168,6 +170,10 @@ fn emit_property_handling(
             property_name: &Arc<str>,
             resolve_info: &ResolveInfo,
         ) -> ContextOutcomeIterator<'a, Self::Vertex, FieldValue> {
+            if property_name.as_ref() == "__typename" {
+                return resolve_property_with(contexts, |vertex| vertex.typename().into());
+            }
+
             match type_name.as_ref() {
                 #arms
                 _ => unreachable!("attempted to read property '{property_name}' on unexpected type: {type_name}"),

trustfall_stubgen/test_data/expected_outputs/hackernews/adapter/adapter_impl.rs

@@ -1,6 +1,6 @@
 use std::sync::{Arc, OnceLock};
 
-use trustfall::{FieldValue, Schema, provider::{ContextIterator, ContextOutcomeIterator, EdgeParameters, ResolveEdgeInfo, ResolveInfo, VertexIterator, resolve_coercion_using_schema}};
+use trustfall::{FieldValue, Schema, provider::{ContextIterator, ContextOutcomeIterator, EdgeParameters, ResolveEdgeInfo, ResolveInfo, Typename, VertexIterator, resolve_coercion_using_schema, resolve_property_with}};
 
 use super::vertex::Vertex;
 
@@ -171,6 +171,9 @@ impl<'a> trustfall::provider::Adapter<'a> for Adapter {
         property_name: &Arc<str>,
         resolve_info: &ResolveInfo,
     ) -> ContextOutcomeIterator<'a, Self::Vertex, FieldValue> {
+        if property_name.as_ref() == "__typename" {
+            return resolve_property_with(contexts, |vertex| vertex.typename().into());
+        }
         match type_name.as_ref() {
             "Comment" => {
                 super::properties::resolve_comment_property(

trustfall_stubgen/test_data/expected_outputs/use_reserved_rust_names_in_schema/adapter/adapter_impl.rs

@@ -1,6 +1,6 @@
 use std::sync::{Arc, OnceLock};
 
-use trustfall::{FieldValue, Schema, provider::{ContextIterator, ContextOutcomeIterator, EdgeParameters, ResolveEdgeInfo, ResolveInfo, VertexIterator, resolve_coercion_using_schema}};
+use trustfall::{FieldValue, Schema, provider::{ContextIterator, ContextOutcomeIterator, EdgeParameters, ResolveEdgeInfo, ResolveInfo, Typename, VertexIterator, resolve_coercion_using_schema, resolve_property_with}};
 
 use super::vertex::Vertex;
 
@@ -68,6 +68,9 @@ impl<'a> trustfall::provider::Adapter<'a> for Adapter {
         property_name: &Arc<str>,
         resolve_info: &ResolveInfo,
     ) -> ContextOutcomeIterator<'a, Self::Vertex, FieldValue> {
+        if property_name.as_ref() == "__typename" {
+            return resolve_property_with(contexts, |vertex| vertex.typename().into());
+        }
         match type_name.as_ref() {
             "const2" => {
                 super::properties::resolve_const2_property(