all: add EDITION_UNSTABLE support

The UNSTABLE edition serves as a sandbox for all features in-development.
The --experimental_edition protoc flag is required to accept it.

Google-Internally, see go/edition-unstable for more details.

Originally authored by Rachel Goldfinger, who asked me to send the change.

Change-Id: If3acc284f70b7690e837d4746202823880a13355
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/727960
Reviewed-by: Lasse Folger <lassefolger@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: stapelberg

internal/filedesc/desc.go

@@ -32,6 +32,7 @@ const (
 	EditionProto3      Edition = 999
 	Edition2023        Edition = 1000
 	Edition2024        Edition = 1001
+	EditionUnstable    Edition = 9999
 	EditionUnsupported Edition = 100000
 )
 

reflect/protodesc/desc.go

@@ -108,7 +108,9 @@ func (o FileOptions) New(fd *descriptorpb.FileDescriptorProto, r Resolver) (prot
 	if f.L1.Path == "" {
 		return nil, errors.New("file path must be populated")
 	}
-	if f.L1.Syntax == protoreflect.Editions && (fd.GetEdition() < editionssupport.Minimum || fd.GetEdition() > editionssupport.Maximum) {
+	if f.L1.Syntax == protoreflect.Editions &&
+		(fd.GetEdition() < editionssupport.Minimum || fd.GetEdition() > editionssupport.Maximum) &&
+		fd.GetEdition() != descriptorpb.Edition_EDITION_UNSTABLE {
 		// Allow cmd/protoc-gen-go/testdata to use any edition for easier
 		// testing of upcoming edition features.
 		if !strings.HasPrefix(fd.GetName(), "cmd/protoc-gen-go/testdata/") {

reflect/protodesc/editions.go

@@ -58,7 +58,7 @@ func getFeatureSetFor(ed filedesc.Edition) *descriptorpb.FeatureSet {
 		return def
 	}
 	edpb := toEditionProto(ed)
-	if defaults.GetMinimumEdition() > edpb || defaults.GetMaximumEdition() < edpb {
+	if (defaults.GetMinimumEdition() > edpb || defaults.GetMaximumEdition() < edpb) && edpb != descriptorpb.Edition_EDITION_UNSTABLE {
 		// This should never happen protodesc.(FileOptions).New would fail when
 		// initializing the file descriptor.
 		// This most likely means the embedded defaults were not updated.