[errors] de-specialize Transient in favor of Tags.

grpc/grpcutil/errors.go

Index: grpc/grpcutil/errors.go
diff --git a/grpc/grpcutil/errors.go b/grpc/grpcutil/errors.go
index 760892e5f5a6c0232add46d4037538043869e238..e34f3216a004f95904eaa54abe83ec1a9afdac76 100644
--- a/grpc/grpcutil/errors.go
+++ b/grpc/grpcutil/errors.go
@@ -5,10 +5,11 @@
 package grpcutil
 
 import (
-	"github.com/luci/luci-go/common/errors"
-
 	"google.golang.org/grpc"
 	"google.golang.org/grpc/codes"
+
+	"github.com/luci/luci-go/common/errors"
+	"github.com/luci/luci-go/common/retry/transient"
 )
 
 var (
@@ -81,30 +82,38 @@ func WrapIfTransient(err error) error {
 	}
 
 	if IsTransientCode(Code(err)) {
-		err = errors.WrapTransient(err)
+		err = transient.Tag.Apply(err)
 	}
 	return err
 }
 
-const grpcCodeKey = "__grpcutil.Code"
+type grpcCodeTag struct{ Key errors.TagKey }

[dnj, 2017/06/27 03:57:03]

QQ: why is "Key" named here (and elsewhere)?

[iannucci, 2017/06/27 18:14:27]

Because TagKey is a pointer type, it can't be embedded. Not that it matters,
because it can't have any methods on it anyway...

+
+func (g grpcCodeTag) With(code codes.Code) errors.TagValue { return errors.MkTagValue(g.Key, code) }
+func (g grpcCodeTag) In(err error) (v codes.Code, ok bool) {
+	d, ok := errors.TagValueIn(g.Key, err)
+	if ok {
+		v = d.(codes.Code)
+	}
+	return
+}
+
+// Tag may be used to associate a gRPC status code with this error.
+//
+// The tag value MUST be a "google.golang.org/grpc/codes".Code.
+var Tag = grpcCodeTag{errors.NewTagKey("gRPC Code")}
 
 // Code returns the gRPC code for a given error.
 //
 // In addition to the functionality of grpc.Code, this will unwrap any wrapped
 // errors before asking for its code.
 func Code(err error) codes.Code {
-	if code := errors.ExtractData(err, grpcCodeKey); code != nil {
-		return code.(codes.Code)
+	if code, ok := Tag.In(err); ok {
+		return code
 	}
 	return grpc.Code(errors.Unwrap(err))
 }
 
-// Annotate begins annotating the error, and adds the given gRPC code.
-// This code may be extracted with the Code function in this package.
-func Annotate(err error, code codes.Code) *errors.Annotator {
-	return errors.Annotate(err).D(grpcCodeKey, code)
-}
-
 // ToGRPCErr is a shorthand for Errf(Code(err), "%s", err)
 func ToGRPCErr(err error) error {
 	return Errf(Code(err), "%s", err)