signer/core: EIP-712 encoded data should not reject a Domain without a ChainId (#21306)

* Do not check for a non-nil ChainId

* Add encoding test

signer/core/signed_data.go

@@ -965,11 +965,7 @@ func isPrimitiveTypeValid(primitiveType string) bool {
 // validate checks if the given domain is valid, i.e. contains at least
 // the minimum viable keys and values
 func (domain *TypedDataDomain) validate() error {
-	if domain.ChainId == nil {
+	if domain.ChainId == nil && len(domain.Name) == 0 && len(domain.Version) == 0 && len(domain.VerifyingContract) == 0 && len(domain.Salt) == 0 {
-		return errors.New("chainId must be specified according to EIP-155")
-	}
-
-	if len(domain.Name) == 0 && len(domain.Version) == 0 && len(domain.VerifyingContract) == 0 && len(domain.Salt) == 0 {
 		return errors.New("domain is undefined")
 	}
 

signer/core/signed_data_test.go

@@ -245,6 +245,10 @@ func TestDomainChainId(t *testing.T) {
 	if _, ok := withoutChainID.Domain.Map()["chainId"]; ok {
 		t.Errorf("Expected the chainId key to not be present in the domain map")
 	}
+	// should encode successfully
+	if _, err := withoutChainID.HashStruct("EIP712Domain", withoutChainID.Domain.Map()); err != nil {
+		t.Errorf("Expected the typedData to encode the domain successfully, got %v", err)
+	}
 	withChainID := core.TypedData{
 		Types: core.Types{
 			"EIP712Domain": []core.Type{
@@ -261,6 +265,10 @@ func TestDomainChainId(t *testing.T) {
 	if _, ok := withChainID.Domain.Map()["chainId"]; !ok {
 		t.Errorf("Expected the chainId key be present in the domain map")
 	}
+	// should encode successfully
+	if _, err := withChainID.HashStruct("EIP712Domain", withChainID.Domain.Map()); err != nil {
+		t.Errorf("Expected the typedData to encode the domain successfully, got %v", err)
+	}
 }
 
 func TestHashStruct(t *testing.T) {