Add config.Resource.PreviousVersions to specify the previous versions of an MR API

pkg/config/resource.go

@@ -401,6 +401,11 @@ type Resource struct {
 	// Version is the API version being generated for the corresponding CRD.
 	Version string
 
+	// PreviousVersions is the list of API versions previously generated for this
+	// resource for multi-versioned managed resources. upjet will attempt to load
+	// the type definitions from these previous versions if configured.
+	PreviousVersions []string
+
 	// ControllerReconcileVersion is the CRD API version the associated
 	// controller will watch & reconcile. If left unspecified,
 	// defaults to the value of Version. This configuration parameter
@@ -536,6 +541,9 @@ type Resource struct {
 	// conflict. By convention, also used in upjet, the field name is preceded by
 	// the value of the generated Kind, for example:
 	// "TagParameters": "ClusterTagParameters"
+	// Deprecated: OverrideFieldNames has been deprecated in favor of loading
+	// the already existing type names from the older versions of the MR APIS
+	// via the PreviousVersions API.
 	OverrideFieldNames map[string]string
 
 	// requiredFields are the fields that will be marked as required in the

pkg/pipeline/run.go

@@ -98,6 +98,10 @@ func Run(pc *config.Provider, rootDir string) { //nolint:gocyclo
 			tfGen := NewTerraformedGenerator(versionGen.Package(), rootDir, group, version)
 			ctrlGen := NewControllerGenerator(rootDir, pc.ModulePath, group)
 
+			if err := versionGen.InsertPreviousObjects(versions); err != nil {
+				panic(errors.Wrapf(err, "cannot insert type definitions from the previous versions into the package scope for group %q", group))
+			}
+
 			for _, name := range sortedResources(resources) {
 				paramTypeName, err := crdGen.Generate(resources[name])
 				if err != nil {

pkg/pipeline/version.go

@@ -5,14 +5,17 @@
 package pipeline
 
 import (
+	"fmt"
 	"go/types"
 	"os"
 	"path/filepath"
 	"strings"
 
 	"github.com/muvaf/typewriter/pkg/wrapper"
 	"github.com/pkg/errors"
+	"golang.org/x/tools/go/packages"
 
+	"github.com/crossplane/upjet/pkg/config"
 	"github.com/crossplane/upjet/pkg/pipeline/templates"
 )
 
@@ -60,3 +63,36 @@ func (vg *VersionGenerator) Generate() error {
 func (vg *VersionGenerator) Package() *types.Package {
 	return vg.pkg
 }
+
+// InsertPreviousObjects inserts into this VersionGenerator's package scope all
+// the type definitions from the previous versions of the managed resource APIs
+// found in the Go package.
+func (vg *VersionGenerator) InsertPreviousObjects(versions map[string]map[string]*config.Resource) error {
+	for _, resources := range versions {
+		for _, r := range resources {
+			for _, v := range r.PreviousVersions {
+				if vg.Version != v {
+					// if this previous version v is not the version we are currently
+					// processing
+					continue
+				}
+				pkgs, err := packages.Load(&packages.Config{
+					Mode: packages.NeedTypes,
+					Dir:  vg.DirectoryPath,
+				}, fmt.Sprintf("zz_%s_types.go", strings.ToLower(r.Kind)))
+				if err != nil {
+					return errors.Wrapf(err, "cannot load the previous versions of %q from path %s", r.Name, vg.pkg.Path())
+				}
+				for _, p := range pkgs {
+					if p.Types == nil || p.Types.Scope() == nil {
+						continue
+					}
+					for _, n := range p.Types.Scope().Names() {
+						vg.pkg.Scope().Insert(p.Types.Scope().Lookup(n))
+					}
+				}
+			}
+		}
+	}
+	return nil
+}