add --format flag for proto/JSON plan bundles (#8825)

This change adds a new flag for emitting plan bundles in the new protobuf wire format. `opa build --format=json|proto`. With `--format=proto`, the bundle contains `/plan.pb` and `/.manifest.pb` in place of `/plan.json`and `/.manifest`. Bundle Reader auto-detects both forms; mixed-format bundles are rejected at read, merge, and write time.

Signed-off-by: Sebastian Spaink <sebastianspaink@gmail.com>

e2e/proto/manifest_test.go

@@ -29,6 +29,11 @@ func TestManifestProtoConsistency(t *testing.T) {
 			{
 				Name:   "Manifest",
 				GoType: reflect.TypeOf(bundle.Manifest{}),
+				// roots_set is wire-form bookkeeping: it preserves the
+				// nil-vs-explicit-empty distinction that Manifest.Roots
+				// (*[]string) carries on the Go side. No Go counterpart by
+				// design.
+				SkipProtoFields: []string{"roots_set"},
 			},
 			{
 				Name:   "WasmResolver",

e2e/proto/protoschemacheck/protoschemacheck.go

@@ -73,6 +73,11 @@ type MessageSpec struct {
 	// is intentionally absent from the proto because consumers consult
 	// their own registry for builtin signatures.
 	SkipGoFields []string
+	// SkipProtoFields names proto fields with no Go counterpart by design —
+	// wire-form bookkeeping that the Go side carries differently. For
+	// example, bundle.Manifest.roots_set distinguishes nil from explicit-
+	// empty on the wire; the Go side already carries that as Roots *[]string.
+	SkipProtoFields []string
 }
 
 // OneofSpec asserts that the named oneof on MessageName has exactly the
@@ -289,6 +294,14 @@ func checkMessage(t *testing.T, declared map[string]protoreflect.MessageDescript
 		}
 	}
 
+	skipProto := map[string]bool{}
+	for _, n := range m.SkipProtoFields {
+		skipProto[n] = true
+		if msg.Fields().ByName(protoreflect.Name(n)) == nil {
+			t.Errorf("%s: SkipProtoFields entry %q does not match any proto field on this message", m.Name, n)
+		}
+	}
+
 	// Validate FieldNameOverride entries point at real Go fields.
 	for goJSONName := range override {
 		if !goJSONNameExists(m.GoType, goJSONName) {
@@ -333,6 +346,9 @@ func checkMessage(t *testing.T, declared map[string]protoreflect.MessageDescript
 		if opaque[name] {
 			continue
 		}
+		if skipProto[name] {
+			continue
+		}
 		// Fields belonging to a oneof handled by an OneofSpec are
 		// validated there, not here. Skip them so the orphan check
 		// doesn't double-fire.