Restore build-tag for conversion and defaulter gen

The build-tag flag is removed but it is still useful to provide a way
to inject a custom build tag that is different from the default build tag.
This custom build tag will allow gengo to load certain conversion and defaults
funcs that reside in files with default build tag which is usually ignored by
gengo.

Signed-off-by: Vu Dinh <vudinh@outlook.com>

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

@@ -20,6 +20,8 @@ import (
 	"fmt"
 
 	"github.com/spf13/pflag"
+
+	"k8s.io/gengo/v2"
 )
 
 // DefaultBasePeerDirs are the peer-dirs nearly everybody will use, i.e. those coming from
@@ -57,13 +59,20 @@ type Args struct {
 	// GoHeaderFile is the path to a boilerplate header file for generated
 	// code.
 	GoHeaderFile string
+
+	// 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
 }
 
 // New returns default arguments for the generator.
 func New() *Args {
 	return &Args{
-		BasePeerDirs: DefaultBasePeerDirs,
-		SkipUnsafe:   false,
+		BasePeerDirs:      DefaultBasePeerDirs,
+		SkipUnsafe:        false,
+		GeneratedBuildTag: gengo.StdBuildTag,
 	}
 }
 
@@ -81,6 +90,7 @@ func (args *Args) AddFlags(fs *pflag.FlagSet) {
 		"If true, will not generate code using unsafe pointer conversions; resulting code may be slower.")
 	fs.StringVar(&args.GoHeaderFile, "go-header-file", "",
 		"the path to a file containing boilerplate header text; the string \"YEAR\" will be replaced with the current 4-digit year")
+	fs.StringVar(&args.GeneratedBuildTag, "build-tag", args.GeneratedBuildTag, "A Go build tag to use to identify files generated by this command. Should be unique.")
 }
 
 // Validate checks the given arguments.

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

@@ -196,7 +196,7 @@ func getManualConversionFunctions(context *generator.Context, pkg *types.Package
 }
 
 func GetTargets(context *generator.Context, args *args.Args) []generator.Target {
-	boilerplate, err := gengo.GoBoilerplate(args.GoHeaderFile, gengo.StdBuildTag, gengo.StdGeneratedBy)
+	boilerplate, err := gengo.GoBoilerplate(args.GoHeaderFile, args.GeneratedBuildTag, gengo.StdGeneratedBy)
 	if err != nil {
 		klog.Fatalf("Failed loading boilerplate: %v", err)
 	}

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

@@ -128,7 +128,7 @@ func main() {
 		generators.NameSystems(),
 		generators.DefaultNameSystem(),
 		myTargets,
-		gengo.StdBuildTag,
+		args.GeneratedBuildTag,
 		pflag.Args(),
 	); err != nil {
 		klog.Fatalf("Error: %v", err)

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

@@ -20,17 +20,27 @@ import (
 	"fmt"
 
 	"github.com/spf13/pflag"
+
+	"k8s.io/gengo/v2"
 )
 
 type Args struct {
 	OutputFile    string
 	ExtraPeerDirs []string // Always consider these as last-ditch possibilities for conversions.
 	GoHeaderFile  string
+
+	// 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
 }
 
 // New returns default arguments for the generator.
 func New() *Args {
-	return &Args{}
+	return &Args{
+		GeneratedBuildTag: gengo.StdBuildTag,
+	}
 }
 
 // AddFlags add the generator flags to the flag set.
@@ -41,6 +51,7 @@ func (args *Args) AddFlags(fs *pflag.FlagSet) {
 		"Comma-separated list of import paths which are considered, after tag-specified peers, for conversions.")
 	fs.StringVar(&args.GoHeaderFile, "go-header-file", "",
 		"the path to a file containing boilerplate header text; the string \"YEAR\" will be replaced with the current 4-digit year")
+	fs.StringVar(&args.GeneratedBuildTag, "build-tag", args.GeneratedBuildTag, "A Go build tag to use to identify files generated by this command. Should be unique.")
 }
 
 // Validate checks the given arguments.

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

@@ -222,7 +222,7 @@ func getManualDefaultingFunctions(context *generator.Context, pkg *types.Package
 }
 
 func GetTargets(context *generator.Context, args *args.Args) []generator.Target {
-	boilerplate, err := gengo.GoBoilerplate(args.GoHeaderFile, gengo.StdBuildTag, gengo.StdGeneratedBy)
+	boilerplate, err := gengo.GoBoilerplate(args.GoHeaderFile, args.GeneratedBuildTag, gengo.StdGeneratedBy)
 	if err != nil {
 		klog.Fatalf("Failed loading boilerplate: %v", err)
 	}

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

@@ -74,7 +74,7 @@ func main() {
 		generators.NameSystems(),
 		generators.DefaultNameSystem(),
 		myTargets,
-		gengo.StdBuildTag,
+		args.GeneratedBuildTag,
 		pflag.Args(),
 	); err != nil {
 		klog.Fatalf("Error: %v", err)