Move the k8s code generator.

cmd/k8scopy/main.go

@@ -0,0 +1,54 @@
+// Copyright 2020 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+// k8scopy is a code reuse mechanism for k8s.io code.
+//
+// kustomize, kyaml, cmd/config are kustomize repo modules that want to reuse
+// some small bits of k8s.io code. These modules cannot depend k8s.io via
+// normal Go import or vendoring because kubectl will depend on these things
+// eventually (see kubernetes-sigs/kustomize/issues/1500), and kubectl's code
+// reuse is tricky. While kubectl remains in the k/k repo, it depends on local
+// relative symlinked paths to a 'staging' version of k8s.io code.  No code
+// imported by kubectl can refer to any other version of k8s.io code, not by
+// Go importing, not by Go vendoring.
+//
+// This main exists to allow "go generate" to copy select k8s.io packages into
+// the kustomize repo at well defined tags in reproducible fashion.  It's
+// a form of vendoring reuse that avoids the problems created by k8s staging.
+// The copied code is labelled as generated and is not otherwise edited.
+//
+// When/if kubectl is finally extracted from k/k to its own repo, it can
+// depend on k8s.io code via normal imports, and then so can kustomize,
+// so this technique can be dropped.
+//
+// Until then, if a bug is found in a particular instance of copied k8s.io
+// (highly unlikely, since only old stable versions are copied), just update
+// the version being copied, re-generate, and if need be adjust call points.
+package main
+
+import (
+	"log"
+	"os"
+
+	"sigs.k8s.io/kustomize/cmd/k8scopy/internal"
+)
+
+func main() {
+	if len(os.Args) < 2 {
+		log.Fatal("Need name of yaml file containing module specs.")
+	}
+	spec := internal.ReadSpec(os.Args[1])
+	c := internal.NewCopier(spec)
+	internal.RunNoOutputCommand("go", "get", spec.Name())
+	for _, p := range spec.Packages {
+		for _, n := range p.Files {
+			if err := c.CopyFile(p.Name, n); err != nil {
+				log.Fatal(err)
+			}
+		}
+	}
+	internal.RunNoOutputCommand(
+		"go", "mod", "edit", "-droprequire="+spec.Module)
+	internal.RunNoOutputCommand("go", "mod", "tidy")
+	internal.RunGetOutputCommand("go", "fmt", "./...")
+}