total rewrite to interface handling; not complete but it compiles

generate/testdata/UnionNoFragments.graphql.go

@@ -0,0 +1,79 @@
+package test
+
+// Code generated by github.com/Khan/genql, DO NOT EDIT.
+
+import (
+	"context"
+
+	"github.com/Khan/genql/graphql"
+)
+
+type Article struct {
+	Typename *string `json:"__typename"`
+}
+
+func (v Article) implementsGraphQLInterfaceLeafContent() {}
+
+type LeafContent interface {
+	implementsGraphQLInterfaceLeafContent()
+}
+
+type UnionNoFragmentsQueryResponse struct {
+	RandomLeaf LeafContent `json:"-"`
+}
+
+func (v *UnionNoFragmentsQueryResponse) UnmarshalJSON(b []byte) error {
+	var firstPass struct {
+		*UnionNoFragmentsQueryResponse
+		RandomLeaf json.RawMessage `json:"randomLeaf"`
+	}
+	firstPass.UnionNoFragmentsQueryResponse = v
+
+	err := json.Unmarshal(b, &typenames)
+	if err != nil {
+		return err
+	}
+
+	var tn struct {
+		TypeName string `json:"__typename"`
+	}
+	err = json.Unmarshal(firstPass.RandomLeaf, &tn)
+	if err != nil {
+		return err
+	}
+	switch tn.TypeName {
+
+	case "Article":
+		v.RandomLeaf = Article{}
+		err = json.Unmarshal(
+			firstPass.RandomLeaf, &v.RandomLeaf)
+
+	case "Video":
+		v.RandomLeaf = Video{}
+		err = json.Unmarshal(
+			firstPass.RandomLeaf, &v.RandomLeaf)
+
+	}
+	if err != nil {
+		return err
+	}
+
+}
+
+type Video struct {
+	Typename *string `json:"__typename"`
+}
+
+func (v Video) implementsGraphQLInterfaceLeafContent() {}
+
+func UnionNoFragmentsQuery(client *graphql.Client) (*UnionNoFragmentsQueryResponse, error) {
+	var retval UnionNoFragmentsQueryResponse
+	err := client.MakeRequest(context.Background(), `
+query UnionNoFragmentsQuery {
+	randomLeaf {
+		__typename
+	}
+}
+`, &retval, nil)
+	return &retval, err
+}