THRIFT-5845: Return TException for union check in Write

Client: go

In compiler generated Write method for union types, return a TException
(TProtocolException) when the number of fields set is not exactly 1, to
help customer logic to decide whether to reuse a connection after an
error.

While I'm here, also do the same thing for the uniqueness check failure
for set fields in Write as well.

compiler/cpp/src/thrift/generate/t_go_generator.cc

@@ -1701,7 +1701,7 @@ void t_go_generator::generate_go_struct_reader(ostream& out,
       out << indent() << "if !isset" << field_name << "{" << '\n';
       indent_up();
       out << indent() << "return thrift.NewTProtocolExceptionWithType(thrift.INVALID_DATA, "
-                         "fmt.Errorf(\"Required field " << field_name << " is not set\"));" << '\n';
+                      << "fmt.Errorf(\"Required field " << field_name << " is not set\"))" << '\n';
       indent_down();
       out << indent() << "}" << '\n';
     }
@@ -1748,7 +1748,8 @@ void t_go_generator::generate_go_struct_writer(ostream& out,
     std::string tstruct_name(publicize(tstruct->get_name()));
     out << indent() << "if c := p.CountSetFields" << tstruct_name << "(); c != 1 {" << '\n';
     indent_up();
-    out << indent() << "return fmt.Errorf(\"%T write union: exactly one field must be set (%d set)\", p, c)" << '\n';
+    out << indent() << "return thrift.NewTProtocolExceptionWithType(thrift.INVALID_DATA, "
+                    << "fmt.Errorf(\"%T write union: exactly one field must be set (%d set)\", p, c))" << '\n';
     indent_down();
     out << indent() << "}" << '\n';
   }
@@ -3719,10 +3720,9 @@ void t_go_generator::generate_serialize_container(ostream& out,
     indent_down();
     out << indent() << "}(" << wrapped_prefix << "[i], " << wrapped_prefix << "[j]) {" << '\n';
     indent_up();
-    out << indent()
-        << "return thrift.PrependError(\"\", fmt.Errorf(\"%T error writing set field: slice is not "
-           "unique\", "
-        << wrapped_prefix << "))" << '\n';
+    out << indent() << "return thrift.NewTProtocolExceptionWithType(thrift.INVALID_DATA, "
+                    << "fmt.Errorf(\"%T error writing set field: slice is not " "unique\", "
+                    << wrapped_prefix << "))" << '\n';
     indent_down();
     out << indent() << "}" << '\n';
     indent_down();

lib/go/test/UnionBinaryTest.thrift

@@ -21,5 +21,6 @@
 union Sample {
   1: map<string, string> u1,
   2: binary u2,
-  3: list<string> u3
+  3: list<string> u3,
+  4: set<string> u4,
 }

lib/go/test/tests/write_texception_test.go

@@ -0,0 +1,69 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements. See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership. The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied. See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package tests
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/apache/thrift/lib/go/test/gopath/src/unionbinarytest"
+	"github.com/apache/thrift/lib/go/thrift"
+)
+
+func TestWriteUnionTException(t *testing.T) {
+	// See https://issues.apache.org/jira/browse/THRIFT-5845
+	s := unionbinarytest.NewSample()
+	proto := thrift.NewTBinaryProtocolConf(thrift.NewTMemoryBuffer(), nil)
+	err := s.Write(context.Background(), proto)
+	t.Log(err)
+	if err == nil {
+		t.Fatal("Writing empty union did not produce error")
+	}
+	var te thrift.TException
+	if !errors.As(err, &te) {
+		t.Fatalf("Error from writing empty union is not TException: (%T) %v", err, err)
+	}
+	if typ := te.TExceptionType(); typ != thrift.TExceptionTypeProtocol && typ != thrift.TExceptionTypeTransport {
+		t.Errorf("Got TExceptionType %v, want one of TProtocolException or TTransportException", typ)
+	}
+}
+
+func TestWriteSetTException(t *testing.T) {
+	// See https://issues.apache.org/jira/browse/THRIFT-5845
+	s := unionbinarytest.NewSample()
+	s.U4 = []string{
+		"foo",
+		"foo", // duplicate
+	}
+	proto := thrift.NewTBinaryProtocolConf(thrift.NewTMemoryBuffer(), nil)
+	err := s.Write(context.Background(), proto)
+	t.Log(err)
+	if err == nil {
+		t.Fatal("Writing duplicate set did not produce error")
+	}
+	var te thrift.TException
+	if !errors.As(err, &te) {
+		t.Fatalf("Error from writing duplicate set is not TException: (%T) %v", err, err)
+	}
+	if typ := te.TExceptionType(); typ != thrift.TExceptionTypeProtocol && typ != thrift.TExceptionTypeTransport {
+		t.Errorf("Got TExceptionType %v, want one of TProtocolException or TTransportException", typ)
+	}
+}