Appropriately Handle Falsy Default Field Values (#1623)

codegen/input.gotpl

@@ -7,7 +7,7 @@
 			asMap[k] = v
 		}
 		{{ range $field := .Fields}}
-			{{- if $field.Default}}
+			{{- if notNil "Default" $field }}
 				if _, present := asMap[{{$field.Name|quote}}] ; !present {
 					asMap[{{$field.Name|quote}}] = {{ $field.Default | dump }}
 				}

codegen/testserver/defaults.graphql

@@ -0,0 +1,20 @@
+extend type Query {
+    defaultParameters(
+        falsyBoolean: Boolean = false
+        truthyBoolean: Boolean = true
+    ): DefaultParametersMirror!
+}
+
+extend type Mutation {
+    defaultInput(input: DefaultInput!): DefaultParametersMirror!
+}
+
+input DefaultInput {
+    falsyBoolean: Boolean = false
+    truthyBoolean: Boolean = true
+}
+
+type DefaultParametersMirror {
+    falsyBoolean: Boolean
+    truthyBoolean: Boolean
+}

codegen/testserver/defaults_test.go

@@ -0,0 +1,68 @@
+package testserver
+
+import (
+	"context"
+	"testing"
+
+	"github.com/99designs/gqlgen/client"
+	"github.com/99designs/gqlgen/graphql/handler"
+	"github.com/stretchr/testify/require"
+)
+
+func assertDefaults(t *testing.T, ret *DefaultParametersMirror) {
+	require.NotNil(t, ret)
+	require.NotNil(t, ret.FalsyBoolean)
+	require.Equal(t, *ret.FalsyBoolean, false)
+	require.NotNil(t, ret.TruthyBoolean)
+	require.Equal(t, *ret.TruthyBoolean, true)
+}
+
+func TestDefaults(t *testing.T) {
+	resolvers := &Stub{}
+	srv := handler.NewDefaultServer(NewExecutableSchema(Config{Resolvers: resolvers}))
+	c := client.New(srv)
+
+	t.Run("default field parameters", func(t *testing.T) {
+		resolvers.QueryResolver.DefaultParameters = func(
+			ctx context.Context,
+			falsyBoolean, truthyBoolean *bool,
+		) (*DefaultParametersMirror, error) {
+			return &DefaultParametersMirror{
+				FalsyBoolean:  falsyBoolean,
+				TruthyBoolean: truthyBoolean,
+			}, nil
+		}
+
+		var resp struct{ DefaultParameters *DefaultParametersMirror }
+		err := c.Post(`query {
+			defaultParameters {
+				falsyBoolean
+				truthyBoolean
+			}
+		}`, &resp)
+		require.NoError(t, err)
+		assertDefaults(t, resp.DefaultParameters)
+	})
+
+	t.Run("default input fields", func(t *testing.T) {
+		resolvers.MutationResolver.DefaultInput = func(
+			ctx context.Context,
+			input DefaultInput,
+		) (*DefaultParametersMirror, error) {
+			return &DefaultParametersMirror{
+				FalsyBoolean:  input.FalsyBoolean,
+				TruthyBoolean: input.TruthyBoolean,
+			}, nil
+		}
+
+		var resp struct{ DefaultInput *DefaultParametersMirror }
+		err := c.Post(`mutation {
+			defaultInput(input: {}) {
+				falsyBoolean
+				truthyBoolean
+			}
+		}`, &resp)
+		require.NoError(t, err)
+		assertDefaults(t, resp.DefaultInput)
+	})
+}