protoc-c: add use_oneof_field_name option

Allows for generic oneof offset lookups based on the name of the oneof,
instead of having to know the field name. All oneof fields should have
the same offset, since they are members of a union.

Fixes #204

Makefile.am

@@ -226,6 +226,23 @@ t_version_version_SOURCES = \
 t_version_version_LDADD = \
 	protobuf-c/libprotobuf-c.la
 
+# Issue #204
+check_PROGRAMS += \
+	t/issue204/issue204
+TESTS += \
+	t/issue204/issue204
+t_issue204_issue204_SOURCES = \
+	t/issue204/issue204.c \
+	t/issue204/issue204.pb-c.c
+t_issue204_issue204_LDADD = \
+	protobuf-c/libprotobuf-c.la
+t/issue204/issue204.pb-c.c t/issue204/issue204.pb-c.h: $(top_builddir)/protoc-c/protoc-gen-c$(EXEEXT) $(top_srcdir)/t/issue204/issue204.proto
+	$(AM_V_GEN)@PROTOC@ --plugin=protoc-gen-c=$(top_builddir)/protoc-c/protoc-gen-c$(EXEEXT) -I$(top_srcdir) --c_out=$(top_builddir) $(top_srcdir)/t/issue204/issue204.proto
+BUILT_SOURCES += \
+	t/issue204/issue204.pb-c.c t/issue204/issue204.pb-c.h
+EXTRA_DIST += \
+	t/issue204/issue204.proto
+
 # Issue #220
 check_PROGRAMS += \
 	t/issue220/issue220

protobuf-c/protobuf-c.proto

@@ -48,6 +48,10 @@ message ProtobufCFileOptions {
 
     // Use const char * instead of char * for string fields
     optional bool const_strings = 4 [default = false];
+
+    // For oneof fields, set ProtobufCFieldDescriptor name field to the
+    // name of the containing oneof, instead of the field name
+    optional bool use_oneof_field_name = 5 [default = false];
 }
 
 extend google.protobuf.FileOptions {

protoc-c/c_field.cc

@@ -107,13 +107,17 @@ void FieldGenerator::GenerateDescriptorInitializerGeneric(io::Printer* printer,
 							  const std::string &descriptor_addr) const
 {
   std::map<std::string, std::string> variables;
+  const OneofDescriptor *oneof = descriptor_->containing_oneof();
+  const ProtobufCFileOptions opt = descriptor_->file()->options().GetExtension(pb_c_file);
   variables["TYPE"] = type_macro;
   variables["classname"] = FullNameToC(FieldScope(descriptor_)->full_name());
   variables["name"] = FieldName(descriptor_);
+  if (opt.use_oneof_field_name())
+    variables["proto_name"] = oneof->name();
+  else
     variables["proto_name"] = descriptor_->name();
   variables["descriptor_addr"] = descriptor_addr;
   variables["value"] = SimpleItoa(descriptor_->number());
-  const OneofDescriptor *oneof = descriptor_->containing_oneof();
   if (oneof != NULL)
     variables["oneofname"] = FullNameToLower(oneof->name());
 

t/issue204/.gitignore

+issue204

t/issue204/issue204.c

+#include <stdlib.h>
+
+#include "t/issue251/issue251.pb-c.h"
+
+int main(void)
+{
+	TwoOneofs msg = TWO_ONEOFS__INIT;
+	const ProtobufCFieldDescriptor *field;
+	unsigned off1, off2, off_name;
+	field = protobuf_c_message_descriptor_get_field_by_name(
+						msg.base.descriptor,
+						"first_oneof");
+	assert (field);
+	off_name = field->offset;
+	field = protobuf_c_message_descriptor_get_field(
+						msg.base.descriptor,
+						10);
+	assert (field);
+	off1 = field->offset;
+	field = protobuf_c_message_descriptor_get_field(
+						msg.base.descriptor,
+						11);
+	assert (field);
+	off2 = field->offset;
+
+	assert (off_name == off1);
+	assert (off1 == off2);
+
+	field = protobuf_c_message_descriptor_get_field_by_name(
+						msg.base.descriptor,
+						"second_oneof");
+	assert (field);
+	off_name = field->offset;
+	field = protobuf_c_message_descriptor_get_field(
+						msg.base.descriptor,
+						20);
+	assert (field);
+	off1 = field->offset;
+	field = protobuf_c_message_descriptor_get_field(
+						msg.base.descriptor,
+						21);
+	assert (field);
+	off2 = field->offset;
+
+	assert (off_name == off1);
+	assert (off1 == off2);
+	return EXIT_SUCCESS;
+}

t/issue204/issue204.proto

+import "protobuf-c/protobuf-c.proto";
+
+option (pb_c_file).use_oneof_field_name = true;
+
+message two_oneofs {
+    oneof first_oneof {
+        bool a = 10;
+        bool b = 11;
+    }
+
+    oneof second_oneof {
+        bool c = 20;
+        bool d = 21;
+    }
+}