Make generated build tag parameterizable for go2idl

Downstream generators that want to reuse the upstream generated types
need to be able to define a different ignore tag (so that they can see
the already generated types).

cmd/libs/go2idl/args/args.go

@@ -39,8 +39,9 @@ import (
 // before calling AddFlags.
 func Default() *GeneratorArgs {
 	generatorArgs := &GeneratorArgs{
-		OutputBase:       DefaultSourceTree(),
-		GoHeaderFilePath: filepath.Join(DefaultSourceTree(), "k8s.io/kubernetes/hack/boilerplate/boilerplate.go.txt"),
+		OutputBase:        DefaultSourceTree(),
+		GoHeaderFilePath:  filepath.Join(DefaultSourceTree(), "k8s.io/kubernetes/hack/boilerplate/boilerplate.go.txt"),
+		GeneratedBuildTag: "ignore_autogenerated",
 	}
 	generatorArgs.AddFlags(pflag.CommandLine)
 	return generatorArgs
@@ -66,6 +67,12 @@ type GeneratorArgs struct {
 	// If true, only verify, don't write anything.
 	VerifyOnly bool
 
+	// GeneratedBuildTag is the tag used to identify code generated by execution
+	// of this type. Each generator should use a different tag, and different
+	// groups of generators (external API that depends on Kube generations) should
+	// keep tags distinct as well.
+	GeneratedBuildTag string
+
 	// Any custom arguments go here
 	CustomArgs interface{}
 }
@@ -77,6 +84,7 @@ func (g *GeneratorArgs) AddFlags(fs *pflag.FlagSet) {
 	fs.StringVarP(&g.GoHeaderFilePath, "go-header-file", "h", g.GoHeaderFilePath, "File containing boilerplate header text. The string YEAR will be replaced with the current 4-digit year.")
 	fs.BoolVar(&g.VerifyOnly, "verify-only", g.VerifyOnly, "If true, only verify existing output, do not write anything.")
 	fs.BoolVar(&g.Recursive, "recursive", g.VerifyOnly, "If true, recurse into all children of input directories.")
+	fs.StringVar(&g.GeneratedBuildTag, "build-tag", g.GeneratedBuildTag, "A Go build tag to use to identify files generated by this command. Should be unique.")
 }
 
 // LoadGoBoilerplate loads the boilerplate file passed to --go-header-file.
@@ -94,7 +102,7 @@ func (g *GeneratorArgs) LoadGoBoilerplate() ([]byte, error) {
 func (g *GeneratorArgs) NewBuilder() (*parser.Builder, error) {
 	b := parser.New()
 	// Ignore all auto-generated files.
-	b.AddBuildTags("ignore_autogenerated")
+	b.AddBuildTags(g.GeneratedBuildTag)
 
 	for _, d := range g.InputDirs {
 		d = strings.TrimLeft(d, "+-*")

cmd/libs/go2idl/conversion-gen/generators/conversion.go

@@ -210,10 +210,7 @@ func Packages(context *generator.Context, arguments *args.GeneratorArgs) generat
 
 	inputs := sets.NewString(arguments.InputDirs...)
 	packages := generator.Packages{}
-	header := append([]byte(
-		`// +build !ignore_autogenerated
-
-`), boilerplate...)
+	header := append([]byte(fmt.Sprintf("// +build !%s\n\n", arguments.GeneratedBuildTag)), boilerplate...)
 	header = append(header, []byte(
 		`
 // This file was autogenerated by conversion-gen. Do not edit it manually!

cmd/libs/go2idl/deepcopy-gen/generators/deepcopy.go

@@ -99,10 +99,7 @@ func Packages(context *generator.Context, arguments *args.GeneratorArgs) generat
 	}
 
 	packages := generator.Packages{}
-	header := append([]byte(
-		`// +build !ignore_autogenerated
-
-`), boilerplate...)
+	header := append([]byte(fmt.Sprintf("// +build !%s\n\n", arguments.GeneratedBuildTag)), boilerplate...)
 	header = append(header, []byte(
 		`
 // This file was autogenerated by deepcopy-gen. Do not edit it manually!

hack/verify-flags/known-flags.txt

@@ -37,6 +37,7 @@ bind-pods-burst
 bind-pods-qps
 build-only
 build-services
+build-tag
 cadvisor-port
 cert-dir
 certificate-authority