feat: custom get signers

proto/cosmos/msg/v1/msg.proto

@@ -27,4 +27,10 @@ extend google.protobuf.MessageOptions {
   // kind in case the signer information is contained within
   // a message inside the cosmos message.
   repeated string signer = 11110000;
+
+  // custom_signer indicates that a message does not define signers in the
+  // standard way using the signer option but instead defines its own custom
+  // way of defining signers. Frameworks and clients will need to provide
+  // custom logic to handle these messages.
+  bool custom_signer = 57938276;
 }

x/tx/go.mod

@@ -31,3 +31,6 @@ require (
 	google.golang.org/grpc v1.55.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )
+
+// temporary replace
+replace cosmossdk.io/api => ../../api

x/tx/signing/context.go

@@ -10,8 +10,9 @@ import (
 	"google.golang.org/protobuf/reflect/protoreflect"
 	"google.golang.org/protobuf/reflect/protoregistry"
 
-	msgv1 "cosmossdk.io/api/cosmos/msg/v1"
 	"cosmossdk.io/core/address"
+
+	msgv1 "cosmossdk.io/api/cosmos/msg/v1"
 )
 
 // Context is a context for retrieving the list of signers from a
@@ -110,7 +111,7 @@ func (c *Context) Validate() error {
 			for j := 0; j < sd.Methods().Len(); j++ {
 				md := sd.Methods().Get(j).Input()
 				_, err := c.getGetSignersFn(md)
-				if err != nil {
+				if err != nil && !errors.Is(err, NeedCustomSignersError) { // don't fail on custom signers
 					errs = append(errs, err)
 				}
 			}
@@ -123,6 +124,11 @@ func (c *Context) Validate() error {
 }
 
 func (c *Context) makeGetSignersFunc(descriptor protoreflect.MessageDescriptor) (getSignersFunc, error) {
+	isCustom := proto.GetExtension(descriptor.Options(), msgv1.E_CustomSigner).(bool)
+	if isCustom {
+		return nil, fmt.Errorf("%w: %s", NeedCustomSignersError, descriptor.FullName())
+	}
+
 	signersFields, err := getSignersFieldNames(descriptor)
 	if err != nil {
 		return nil, err
@@ -316,11 +322,28 @@ func (c *Context) ValidatorAddressCodec() address.Codec {
 	return c.validatorAddressCodec
 }
 
-// FileResolver returns the proto file resolver used by the context.
+// FileResolver returns the protobuf file resolver used by the context.
 func (c *Context) FileResolver() ProtoFileResolver {
 	return c.fileResolver
 }
 
+// TypeResolver returns the protobuf type resolver used by the context.
 func (c *Context) TypeResolver() protoregistry.MessageTypeResolver {
 	return c.typeResolver
 }
+
+// DefineCustomGetSigners defines a custom GetSigners function for a given
+// message type. It is defined as a function rather than a method on Context
+// because of how go generics work.
+//
+// NOTE: if a custom signers function is defined, the message type used to
+// define this function MUST be the concrete type passed to GetSigners,
+// otherwise a runtime type error will occur.
+func DefineCustomGetSigners[T proto.Message](ctx *Context, getSigners func(T) ([][]byte, error)) {
+	t := *new(T)
+	ctx.getSignersFuncs[t.ProtoReflect().Descriptor().FullName()] = func(msg proto.Message) ([][]byte, error) {
+		return getSigners(msg.(T))
+	}
+}
+
+var NeedCustomSignersError = errors.New("need custom signers function")