Implement UniqueOperationNames validator

validator/unique_operation_names.go

@@ -0,0 +1,20 @@
+package validator
+
+import (
+	"github.com/vektah/gqlparser"
+)
+
+func init() {
+	addRule("UniqueOperationNames", func(observers *Events, addError addErrFunc) {
+		seen := map[string]bool{}
+
+		observers.OnOperation(func(walker *Walker, operation *gqlparser.OperationDefinition) {
+			if seen[operation.Name] {
+				addError(
+					Message(`There can be only one operation named "%s".`, operation.Name),
+				)
+			}
+			seen[operation.Name] = true
+		})
+	})
+}

validator/validate_test.go

@@ -47,6 +47,7 @@ func TestSpec(t *testing.T) {
 	t.Run("UniqueDirectivesPerLocation", runSpec(schemas, deviations, "../spec/validation/UniqueDirectivesPerLocation.yml"))
 	t.Run("UniqueFragmentNames", runSpec(schemas, deviations, "../spec/validation/UniqueFragmentNames.yml"))
 	t.Run("UniqueInputFieldNames", runSpec(schemas, deviations, "../spec/validation/UniqueInputFieldNames.yml"))
+	t.Run("UniqueOperationNames", runSpec(schemas, deviations, "../spec/validation/UniqueOperationNames.yml"))
 }
 
 func runSpec(schemas []*gqlparser.Schema, deviations map[string]*Spec, filename string) func(t *testing.T) {