Support references to external types for 3rd party use

staging/src/k8s.io/code-generator/cmd/applyconfiguration-gen/args/args.go

@@ -20,20 +20,51 @@ import (
 	"fmt"
 	"path"
 
+	"github.com/spf13/pflag"
 	"k8s.io/gengo/args"
+	"k8s.io/gengo/types"
 
 	codegenutil "k8s.io/code-generator/pkg/util"
 )
 
+// ClientGenArgs is a wrapper for arguments to applyconfiguration-gen.
+type CustomArgs struct {
+	// ExternalApplyConfigurations provides the locations of externally generated
+	// apply configuration types for types referenced by the go structs provided as input.
+	// Locations are provided as a comma separated list of <package>.<typeName>:<applyconfiguration-package>
+	// entries.
+	//
+	// E.g. if a type references appsv1.Deployment, the location of its apply configuration should
+	// be provided:
+	//   k8s.io/api/apps/v1.Deployment:k8s.io/client-go/applyconfigurations/apps/v1
+	//
+	// meta/v1 types (TypeMeta and ObjectMeta) are always included and do not need to be passed in.
+	ExternalApplyConfigurations map[types.Name]string
+}
+
 // NewDefaults returns default arguments for the generator.
-func NewDefaults() *args.GeneratorArgs {
+func NewDefaults() (*args.GeneratorArgs, *CustomArgs) {
 	genericArgs := args.Default().WithoutDefaultFlagParsing()
+	customArgs := &CustomArgs{
+		ExternalApplyConfigurations: map[types.Name]string{
+			// Always include TypeMeta and ObjectMeta. They are sufficient for the vast majority of use cases.
+			{Package: "k8s.io/apimachinery/pkg/apis/meta/v1", Name: "TypeMeta"}:   "k8s.io/client-go/applyconfigurations/meta/v1",
+			{Package: "k8s.io/apimachinery/pkg/apis/meta/v1", Name: "ObjectMeta"}: "k8s.io/client-go/applyconfigurations/meta/v1",
+		},
+	}
+	genericArgs.CustomArgs = customArgs
 
 	if pkg := codegenutil.CurrentPackage(); len(pkg) != 0 {
 		genericArgs.OutputPackagePath = path.Join(pkg, "pkg/client/applyconfigurations")
 	}
 
-	return genericArgs
+	return genericArgs, customArgs
+}
+
+func (ca *CustomArgs) AddFlags(fs *pflag.FlagSet, inputBase string) {
+	pflag.Var(NewExternalApplyConfigurationValue(&ca.ExternalApplyConfigurations, nil), "external-applyconfigurations",
+		"list of comma separated external apply configurations locations in <type-package>.<type-name>:<applyconfiguration-package> form."+
+			"For example: k8s.io/api/apps/v1.Deployment:k8s.io/client-go/applyconfigurations/apps/v1")
 }
 
 // Validate checks the given arguments.

staging/src/k8s.io/code-generator/cmd/applyconfiguration-gen/args/externaltypes.go

@@ -0,0 +1,125 @@
+/*
+Copyright 2021 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package args
+
+import (
+	"bytes"
+	"encoding/csv"
+	"flag"
+	"fmt"
+	"strings"
+
+	"k8s.io/gengo/types"
+)
+
+type externalApplyConfigurationValue struct {
+	externals *map[types.Name]string
+	changed   bool
+}
+
+func NewExternalApplyConfigurationValue(externals *map[types.Name]string, def []string) *externalApplyConfigurationValue {
+	val := new(externalApplyConfigurationValue)
+	val.externals = externals
+	if def != nil {
+		if err := val.set(def); err != nil {
+			panic(err)
+		}
+	}
+	return val
+}
+
+var _ flag.Value = &externalApplyConfigurationValue{}
+
+func (s *externalApplyConfigurationValue) set(vs []string) error {
+	if !s.changed {
+		*s.externals = map[types.Name]string{}
+	}
+
+	for _, input := range vs {
+		typ, pkg, err := parseExternalMapping(input)
+		if err != nil {
+			return err
+		}
+		if _, ok := (*s.externals)[typ]; ok {
+			return fmt.Errorf("duplicate type found in --external-applyconfigurations: %v", typ)
+		}
+		(*s.externals)[typ] = pkg
+	}
+
+	return nil
+}
+
+func (s *externalApplyConfigurationValue) Set(val string) error {
+	vs, err := readAsCSV(val)
+	if err != nil {
+		return err
+	}
+	if err := s.set(vs); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (s *externalApplyConfigurationValue) Type() string {
+	return "string"
+}
+
+func (s *externalApplyConfigurationValue) String() string {
+	var strs []string
+	for k, v := range *s.externals {
+		strs = append(strs, fmt.Sprintf("%s.%s:%s", k.Package, k.Name, v))
+	}
+	str, _ := writeAsCSV(strs)
+	return "[" + str + "]"
+}
+
+func readAsCSV(val string) ([]string, error) {
+	if val == "" {
+		return []string{}, nil
+	}
+	stringReader := strings.NewReader(val)
+	csvReader := csv.NewReader(stringReader)
+	return csvReader.Read()
+}
+
+func writeAsCSV(vals []string) (string, error) {
+	b := &bytes.Buffer{}
+	w := csv.NewWriter(b)
+	err := w.Write(vals)
+	if err != nil {
+		return "", err
+	}
+	w.Flush()
+	return strings.TrimSuffix(b.String(), "\n"), nil
+}
+
+func parseExternalMapping(mapping string) (typ types.Name, pkg string, err error) {
+	parts := strings.Split(mapping, ":")
+	if len(parts) != 2 {
+		return types.Name{}, "", fmt.Errorf("expected string of the form <package>.<typeName>:<applyconfiguration-package> but got %s", mapping)
+	}
+	packageTypeStr := parts[0]
+	pkg = parts[1]
+	ptParts := strings.Split(packageTypeStr, ".")
+	if len(ptParts) != 2 {
+		return types.Name{}, "", fmt.Errorf("expected package and type of the form <package>#<typeName> but got %s", packageTypeStr)
+	}
+	structPkg := ptParts[0]
+	structType := ptParts[1]
+
+	return types.Name{Package: structPkg, Name: structType}, pkg, nil
+}

staging/src/k8s.io/code-generator/cmd/applyconfiguration-gen/generators/packages.go

@@ -28,6 +28,7 @@ import (
 	"k8s.io/gengo/types"
 	"k8s.io/klog/v2"
 
+	applygenargs "k8s.io/code-generator/cmd/applyconfiguration-gen/args"
 	clientgentypes "k8s.io/code-generator/cmd/client-gen/types"
 )
 
@@ -59,7 +60,8 @@ func Packages(context *generator.Context, arguments *args.GeneratorArgs) generat
 	}
 
 	pkgTypes := packageTypesForInputDirs(context, arguments.InputDirs, arguments.OutputPackagePath)
-	refs := refGraphForReachableTypes(pkgTypes)
+	initialTypes := arguments.CustomArgs.(*applygenargs.CustomArgs).ExternalApplyConfigurations
+	refs := refGraphForReachableTypes(pkgTypes, initialTypes)
 
 	groupVersions := make(map[string]clientgentypes.GroupVersions)
 	groupGoNames := make(map[string]string)

staging/src/k8s.io/code-generator/cmd/applyconfiguration-gen/generators/refgraph.go

@@ -28,8 +28,8 @@ type refGraph map[types.Name]string
 
 // refGraphForReachableTypes returns a refGraph that contains all reachable types from
 // the root clientgen types of the provided packages.
-func refGraphForReachableTypes(pkgTypes map[string]*types.Package) refGraph {
+func refGraphForReachableTypes(pkgTypes map[string]*types.Package, initialTypes map[types.Name]string) refGraph {
-	refs := refGraph{}
+	var refs refGraph = initialTypes
 
 	// Include only types that are reachable from the root clientgen types.
 	// We don't want to generate apply configurations for types that are not reachable from a root

staging/src/k8s.io/code-generator/cmd/applyconfiguration-gen/main.go

@@ -32,9 +32,10 @@ import (
 
 func main() {
 	klog.InitFlags(nil)
-	genericArgs := generatorargs.NewDefaults()
+	genericArgs, customArgs := generatorargs.NewDefaults()
 	genericArgs.GoHeaderFilePath = filepath.Join(args.DefaultSourceTree(), util.BoilerplatePath())
 	genericArgs.AddFlags(pflag.CommandLine)
+	customArgs.AddFlags(pflag.CommandLine, "k8s.io/kubernetes/pkg/apis") // TODO: move this input path out of client-gen
 	if err := flag.Set("logtostderr", "true"); err != nil {
 		klog.Fatalf("Error: %v", err)
 	}