add omitempty options

This change adds a `gogoproto.omitempty` option that can be used (in
conjunction with `(gogoproto.nullable) = false`) for non-nullable
message fields.

When a message field is not nullable, its tag is always encoded - even
if all message fields are unset. The `omitempty` option changes the
marshalling code to check an `Empty()` method on that message, which
must be defined by the user. The result is that when the message is
empty, the encoding matches the one we would get if the field was
nullable and the pointer is unset.

Makefile

@@ -140,6 +140,7 @@ regenerate:
 	make -C test/issue620 regenerate
 	make -C test/protobuffer regenerate
 	make -C test/issue630 regenerate
+	make -C test/omitempty regenerate
 
 	make gofmt
 

gogoproto/gogo.proto

@@ -141,4 +141,11 @@ extend google.protobuf.FieldOptions {
 	optional bool stdduration = 65011;
 	optional bool wktpointer = 65012;
 
+
+	// omitempty is used to skip marshaling non-nullable fields which are empty
+	// (unset). The field's type must implement an `.Empty()` method which will be
+	// consulted prior to marshaling.
+	//
+	// Added by cockroach.
+	optional bool omitempty = 65013;
 }

gogoproto/helper.go

@@ -39,6 +39,10 @@ func IsNullable(field *google_protobuf.FieldDescriptorProto) bool {
 	return proto.GetBoolExtension(field.Options, E_Nullable, true)
 }
 
+func IsOmitEmpty(field *google_protobuf.FieldDescriptorProto) bool {
+	return proto.GetBoolExtension(field.Options, E_Omitempty, false)
+}
+
 func IsStdTime(field *google_protobuf.FieldDescriptorProto) bool {
 	return proto.GetBoolExtension(field.Options, E_Stdtime, false)
 }

plugin/marshalto/marshalto.go

@@ -338,6 +338,7 @@ func (p *marshalto) generateField(proto3 bool, numGen NumGen, file *generator.Fi
 
 	protoSizer := gogoproto.IsProtoSizer(file.FileDescriptorProto, message.DescriptorProto)
 	doNilCheck := gogoproto.NeedsNilCheck(proto3, field)
+	omitEmpty := gogoproto.IsOmitEmpty(field)
 	if required && nullable {
 		p.P(`if m.`, fieldname, `== nil {`)
 		p.In()
@@ -354,6 +355,10 @@ func (p *marshalto) generateField(proto3 bool, numGen NumGen, file *generator.Fi
 	} else if doNilCheck {
 		p.P(`if m.`, fieldname, ` != nil {`)
 		p.In()
+	} else if omitEmpty {
+		p.P(`// Field has gogoproto.omitempty set.`)
+		p.P(`if !m.`, fieldname, `.Empty() {`)
+		p.In()
 	}
 	packed := field.IsPacked() || (proto3 && field.IsPacked3())
 	wireType := field.WireType()
@@ -689,6 +694,7 @@ func (p *marshalto) generateField(proto3 bool, numGen NumGen, file *generator.Fi
 			nullableMsg := nullable && (m.ValueField.GetType() == descriptor.FieldDescriptorProto_TYPE_MESSAGE ||
 				gogoproto.IsCustomType(field) && m.ValueField.IsBytes())
 			plainBytes := m.ValueField.IsBytes() && !gogoproto.IsCustomType(field)
+			omitEmpty := gogoproto.IsOmitEmpty(field)
 			if nullableMsg {
 				p.P(`if `, accessor, ` != nil { `)
 				p.In()
@@ -699,10 +705,14 @@ func (p *marshalto) generateField(proto3 bool, numGen NumGen, file *generator.Fi
 					p.P(`if `, accessor, ` != nil {`)
 				}
 				p.In()
+			} else if omitEmpty {
+				p.P(`// Field has gogoproto.omitempty set.`)
+				p.P(`if !`, accessor, `.Empty() {`)
+				p.In()
 			}
 			p.mapField(numGen, field, m.ValueAliasField, accessor, protoSizer)
 			p.encodeKey(2, wireToType(valuewire))
-			if nullableMsg || plainBytes {
+			if nullableMsg || plainBytes || omitEmpty {
 				p.Out()
 				p.P(`}`)
 			}
@@ -877,7 +887,7 @@ func (p *marshalto) generateField(proto3 bool, numGen NumGen, file *generator.Fi
 	default:
 		panic("not implemented")
 	}
-	if (required && nullable) || repeated || doNilCheck {
+	if (required && nullable) || repeated || doNilCheck || omitEmpty {
 		p.Out()
 		p.P(`}`)
 	}

protoc-gen-gogo/generator/helper.go

@@ -284,6 +284,11 @@ func (g *Generator) GetMapValueField(field, valField *descriptor.FieldDescriptor
 	if err := proto.SetExtension(valField.Options, gogoproto.E_Nullable, &nullable); err != nil {
 		g.Fail(err.Error())
 	}
+
+	omitEmpty := gogoproto.IsOmitEmpty(field)
+	if err := proto.SetExtension(valField.Options, gogoproto.E_Omitempty, &omitEmpty); err != nil {
+		g.Fail(err.Error())
+	}
 	return valField
 }
 

test/omitempty/Makefile

@@ -0,0 +1,32 @@
+# Protocol Buffers for Go with Gadgets
+#
+# Copyright (c) 2015, The GoGo Authors. All rights reserved.
+# http://github.com/gogo/protobuf
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+#     * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#     * Redistributions in binary form must reproduce the above
+# copyright notice, this list of conditions and the following disclaimer
+# in the documentation and/or other materials provided with the
+# distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+# "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+# LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+# A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+# OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+# DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+# THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+# (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+# OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+regenerate:
+	go install github.com/gogo/protobuf/protoc-gen-combo
+	go install github.com/gogo/protobuf/protoc-gen-gogo
+	protoc-gen-combo --gogo_out=. --version="3.0.0" --proto_path=../../protobuf/:../../../../../:. omitempty.proto

test/omitempty/combos/both/mymethod.go

@@ -0,0 +1,5 @@
+package omitempty
+
+func (o *OmitEmpty_Inner) Empty() bool {
+	return o.Foo == 0
+}