copy old imports through before gofmt prunes

internal/rewrite/rewriter.go

@@ -5,6 +5,8 @@ import (
 	"go/ast"
 	"go/token"
 	"io/ioutil"
+	"path/filepath"
+	"strconv"
 
 	"golang.org/x/tools/go/packages"
 )
@@ -62,7 +64,7 @@ func (r *Rewriter) GetMethodBody(structname string, methodname string) string {
 				if d.Name.Name != methodname {
 					continue
 				}
-				if d.Recv.List == nil {
+				if d.Recv == nil || d.Recv.List == nil {
 					continue
 				}
 				recv := d.Recv.List[0].Type
@@ -85,3 +87,37 @@ func (r *Rewriter) GetMethodBody(structname string, methodname string) string {
 
 	return ""
 }
+
+func (r *Rewriter) ExistingImports(filename string) []Import {
+	filename, err := filepath.Abs(filename)
+	if err != nil {
+		panic(err)
+	}
+	for _, f := range r.pkg.Syntax {
+		pos := r.pkg.Fset.Position(f.Pos())
+
+		if filename != pos.Filename {
+			continue
+		}
+
+		var imps []Import
+		for _, i := range f.Imports {
+			name := ""
+			if i.Name != nil {
+				name = i.Name.Name
+			}
+			path, err := strconv.Unquote(i.Path.Value)
+			if err != nil {
+				panic(err)
+			}
+			imps = append(imps, Import{name, path})
+		}
+		return imps
+	}
+	return nil
+}
+
+type Import struct {
+	Alias      string
+	ImportPath string
+}

internal/rewrite/rewriter_test.go

@@ -3,6 +3,7 @@ package rewrite
 import (
 	"testing"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -19,4 +20,17 @@ func TestRewriter(t *testing.T) {
 
 	// trailing comment
 `, body)
+
+	imps := r.ExistingImports("testdata/example.go")
+	require.Len(t, imps, 2)
+	assert.Equal(t, []Import{
+		{
+			Alias:      "",
+			ImportPath: "fmt",
+		},
+		{
+			Alias:      "lol",
+			ImportPath: "bytes",
+		},
+	}, imps)
 }

internal/rewrite/testdata/example.go

@@ -1,5 +1,9 @@
 package testdata
 
+import "fmt"
+
+import lol "bytes"
+
 type Foo struct {
 	Field int
 }
@@ -12,3 +16,9 @@ func (m *Foo) Method(arg int) {
 
 	// trailing comment
 }
+
+func (m *Foo) String() string {
+	var buf lol.Buffer
+	buf.WriteString(fmt.Sprintf("%d", m.Field))
+	return buf.String()
+}

plugin/resolvergen/resolver.go

@@ -89,7 +89,9 @@ func (m *Plugin) generatePerSchema(data *codegen.Data) error {
 		if o.HasResolvers() {
 			fn := gqlToResolverName(data.Config.Resolver.Dir(), o.Position.Src.Name)
 			if files[fn] == nil {
-				files[fn] = &File{}
+				files[fn] = &File{
+					imports: rewriter.ExistingImports(fn),
+				}
 			}
 
 			files[fn].Objects = append(files[fn].Objects, o)
@@ -166,6 +168,18 @@ type File struct {
 	//resolver method implementations, for example when extending a type in a different graphql schema file
 	Objects   []*codegen.Object
 	Resolvers []*Resolver
+	imports   []rewrite.Import
+}
+
+func (f *File) Imports() string {
+	for _, imp := range f.imports {
+		if imp.Alias == "" {
+			templates.CurrentImports.Reserve(imp.ImportPath)
+		} else {
+			templates.CurrentImports.Reserve(imp.ImportPath, imp.Alias)
+		}
+	}
+	return ""
 }
 
 type Resolver struct {

plugin/resolvergen/resolver.gotpl

@@ -12,6 +12,8 @@
 {{ reserveImport "github.com/99designs/gqlgen/graphql" }}
 {{ reserveImport "github.com/99designs/gqlgen/graphql/introspection" }}
 
+{{ .Imports }}
+
 {{ if .HasRoot }}
 	type {{.ResolverType}} struct {}
 {{ end }}