Update UniquenessKey for when Element is/isn't nullable (#896)

codegen/config/binder.go

@@ -285,7 +285,12 @@ func (t *TypeReference) UniquenessKey() string {
 		nullability = "N"
 	}
 
-	return nullability + t.Definition.Name + "2" + templates.TypeIdentifier(t.GO)
+	var elemNullability = ""
+	if t.GQL.Elem != nil && t.GQL.Elem.NonNull {
+		// Fix for #896
+		elemNullability = "ᚄ"
+	}
+	return nullability + t.Definition.Name + "2" + templates.TypeIdentifier(t.GO) + elemNullability
 }
 
 func (t *TypeReference) MarshalFunc() string {

codegen/testserver/issue896.graphql

@@ -0,0 +1,18 @@
+# This example should build stable output. If the file content starts
+# alternating nondeterministically between two outputs, then see
+# https://github.com/99designs/gqlgen/issues/896.
+
+extend schema {
+  query: Query
+  subscription: Subscription
+}
+
+type CheckIssue896 {id: Int}
+
+extend type Query {
+  issue896a: [CheckIssue896!] # Note the "!" or lack thereof.
+}
+
+extend type Subscription {
+  issue896b: [CheckIssue896] # Note the "!" or lack thereof.
+}

codegen/testserver/resolver.go

@@ -194,6 +194,9 @@ func (r *queryResolver) Shapes(ctx context.Context) ([]Shape, error) {
 func (r *queryResolver) NoShape(ctx context.Context) (Shape, error) {
 	panic("not implemented")
 }
+func (r *queryResolver) Issue896a(ctx context.Context) ([]*CheckIssue896, error) {
+	panic("not implemented")
+}
 func (r *queryResolver) MapStringInterface(ctx context.Context, in map[string]interface{}) (map[string]interface{}, error) {
 	panic("not implemented")
 }
@@ -263,6 +266,9 @@ func (r *subscriptionResolver) DirectiveDouble(ctx context.Context) (<-chan *str
 func (r *subscriptionResolver) DirectiveUnimplemented(ctx context.Context) (<-chan *string, error) {
 	panic("not implemented")
 }
+func (r *subscriptionResolver) Issue896b(ctx context.Context) (<-chan []*CheckIssue896, error) {
+	panic("not implemented")
+}
 
 type userResolver struct{ *Resolver }
 

codegen/type.go

@@ -1,15 +1,29 @@
 package codegen
 
 import (
+	"fmt"
+
 	"github.com/99designs/gqlgen/codegen/config"
 )
 
 func (b *builder) buildTypes() map[string]*config.TypeReference {
 	ret := map[string]*config.TypeReference{}
+	var key string
+	var existing *config.TypeReference
+	var found bool
 
 	for _, ref := range b.Binder.References {
 		for ref != nil {
-			ret[ref.UniquenessKey()] = ref
+			key = ref.UniquenessKey()
+			if existing, found = ret[key]; found {
+				// Simplistic check of content which is obviously different.
+				existingGQL := fmt.Sprintf("%v", existing.GQL)
+				newGQL := fmt.Sprintf("%v", ref.GQL)
+				if existingGQL != newGQL {
+					panic(fmt.Sprintf("non-unique key \"%s\", trying to replace %s with %s", key, existingGQL, newGQL))
+				}
+			}
+			ret[key] = ref
 
 			ref = ref.Elem()
 		}