work in progress for generating nulls for gqlgen types

main.go

package main

import (
	"fmt"
	"go/importer"
	"go/types"
	"log"

	"github.com/99designs/gqlgen/api"
	"github.com/99designs/gqlgen/codegen/config"
	"github.com/99designs/gqlgen/plugin"
	"github.com/99designs/gqlgen/plugin/modelgen"
	"github.com/vektah/gqlparser/v2/ast"
)

var (
	sql_NullTime   types.Type
	sql_NullString types.Type
	sql_Null       types.Type
)

func init() {
	{
		pkg, err := importer.Default().Import("database/sql")
		if err != nil {
			panic(err)
		}
		sql_NullTime = pkg.Scope().Lookup("NullTime").Type()
		sql_NullString = pkg.Scope().Lookup("NullString").Type()
		sql_NullString = pkg.Scope().Lookup("Null").Type()
	}
}

func main() {
	cfg, err := config.LoadConfigFromDefaultLocations()
	if err != nil {
		log.Fatal(err)
	}

	if err := api.Generate(cfg, ReplaceModelgen()); err != nil {
		log.Fatal(err)
	}
}

func ReplaceModelgen() api.Option {
	m := (modelgen.New()).(*modelgen.Plugin)
	m.FieldHook = FieldHook
	p := &Plugin{m}
	return api.ReplacePlugin(p)
}

var _ plugin.ConfigMutator = &Plugin{}

type Plugin struct {
	m *modelgen.Plugin
}

func (p *Plugin) Name() string { return p.m.Name() }

func (p *Plugin) MutateConfig(cfg *config.Config) error {
	return p.m.MutateConfig(cfg)
}

func FieldHook(td *ast.Definition, fd *ast.FieldDefinition, f *modelgen.Field) (*modelgen.Field, error) {
	if !fd.Type.NonNull {
		if p, ok := f.Type.(*types.Pointer); ok {
			switch v := p.Elem().(type) {
			case *types.Basic:
				switch v.Kind() {
				case types.String:
					f.Type = sql_NullString
				default:
					return f, fmt.Errorf("do not support nulls for basic type: %v", v)
				}
			case *types.Named:
				pkg := v.Obj().Pkg()
				switch pkgPath := pkg.Name(); pkgPath {
				case "time":
					switch name := v.Obj().Name(); name {
					case "Time":
						f.Type = sql_NullTime
					default:
						return f, fmt.Errorf("do not support null types in package %s for type: %v", pkgPath, name)
					}
				default:
					return f, fmt.Errorf("do not support null types for package: %v", pkgPath)
				}
			default:
				return f, fmt.Errorf("do not support nulls for type: %T", v)
			}
		}
	}
	// fd.Type = f.Type
	return modelgen.DefaultFieldMutateHook(td, fd, f)
}