Improve error messages when __typename is missing on an union selection

Author: tomhoule

graphql_client/tests/union_query.rs

@@ -56,16 +56,20 @@ fn fragment_on_union() {
 
     let expected = fragment_on_union::ResponseData {
         names: Some(vec![
-            fragment_on_union::MyQueryNames::Person(fragment_on_union::MyQueryNamesOnPerson {
-                first_name: "Audrey".to_string(),
-                last_name: Some("Lorde".to_string()),
-            }),
-            fragment_on_union::MyQueryNames::Dog(fragment_on_union::MyQueryNamesOnDog {
+            fragment_on_union::FragmentOnUnionNames::Person(
+                fragment_on_union::MyQueryNamesOnPerson {
+                    first_name: "Audrey".to_string(),
+                    last_name: Some("Lorde".to_string()),
+                },
+            ),
+            fragment_on_union::FragmentOnUnionNames::Dog(fragment_on_union::MyQueryNamesOnDog {
                 name: "Laïka".to_string(),
             }),
-            fragment_on_union::MyQueryNames::Organization(fragment_on_union::MyQueryNamesOnOrganization {
-                title: "Mozilla".to_string(),
-            }),
+            fragment_on_union::FragmentOnUnionNames::Organization(
+                fragment_on_union::MyQueryNamesOnOrganization {
+                    title: "Mozilla".to_string(),
+                },
+            ),
             fragment_on_union::MyQueryNames::Dog(fragment_on_union::MyQueryNamesOnDog {
                 name: "Norbert".to_string(),
             }),

graphql_client/tests/unions/union_query.graphql

@@ -29,7 +29,6 @@ fragment NamesFragment on NamedThing {
 
 query FragmentOnUnion {
   names {
-    __typename
     ...NamesFragment
   }
 }

graphql_client_codegen/src/codegen.rs

@@ -90,14 +90,8 @@ pub fn response_for_query(
             ))?
         }
 
-        definitions.extend(
-            definition
-                .field_impls_for_selection(&context, &selection, &prefix)
-                .unwrap(),
-        );
-        definition
-            .response_fields_for_selection(&context, &selection, &prefix)
-            .unwrap()
+        definitions.extend(definition.field_impls_for_selection(&context, &selection, &prefix)?);
+        definition.response_fields_for_selection(&context, &selection, &prefix)?
     };
 
     let enum_definitions = context.schema.enums.values().filter_map(|enm| {

graphql_client_codegen/src/interfaces.rs

@@ -131,7 +131,7 @@ impl GqlInterface {
         let name = Ident::new(&prefix, Span::call_site());
         let derives = query_context.response_derives();
 
-        selection.extract_typename().ok_or_else(|| {
+        selection.extract_typename(query_context).ok_or_else(|| {
             format_err!(
                 "Missing __typename in selection for the {} interface (type: {})",
                 prefix,

graphql_client_codegen/src/selection.rs

@@ -41,7 +41,10 @@ impl SelectionItem {
 pub struct Selection(pub Vec<SelectionItem>);
 
 impl Selection {
-    pub fn extract_typename(&self) -> Option<&SelectionField> {
+    pub(crate) fn extract_typename(
+        &self,
+        context: &crate::query::QueryContext,
+    ) -> Option<&SelectionField> {
         self.0.iter().filter_map(|f| f.as_typename()).next()
     }
 }
@@ -88,6 +91,14 @@ mod tests {
     use super::*;
     use graphql_parser;
 
+    #[test]
+    fn selection_extract_typename_simple_case() {
+        let mut selection = Selection(Vec::new());
+        let context = query::QueryContext::new_empty();
+
+        assert!(selection.extract_typename(&context).is_none());
+    }
+
     #[test]
     fn selection_from_graphql_parser_selection_set() {
         let query = r##"

graphql_client_codegen/src/unions.rs

@@ -105,7 +105,8 @@ impl GqlUnion {
         let struct_name = Ident::new(prefix, Span::call_site());
         let derives = query_context.response_derives();
 
-        let typename_field = selection.extract_typename();
+        // TODO: do this inside fragments
+        let typename_field = selection.extract_typename(query_context);
 
         if typename_field.is_none() {
             Err(UnionError::MissingTypename {

graphql_query_derive/src/lib.rs

@@ -19,8 +19,10 @@ pub fn graphql_query_derive(input: proc_macro::TokenStream) -> proc_macro::Token
     let ast = syn::parse2(input).expect("Derive input is well formed");
     let (query_path, schema_path) = build_query_and_schema_path(&ast);
     let options = build_graphql_client_derive_options(&ast);
-    let gen = generate_module_token_stream(query_path, schema_path, Some(options)).unwrap();
-    gen.into()
+    match generate_module_token_stream(query_path, schema_path, Some(options)) {
+        Ok(module) => module.into(),
+        Err(err) => panic!("{}", err),
+    }
 }
 
 fn build_query_and_schema_path(