protopatch

Patch protoc plugin output with Go-specific features. The protoc-gen-go-patch command wraps calls to Go code generators like protoc-gen-go or protoc-gen-go-grpc and patches the Go syntax before being written to disk.

Install

go install github.com/alta/protopatch/cmd/protoc-gen-go-patch

Usage

After installing protoc-gen-go-patch, use it by specifying it with a --go-patch_out=... argument to protoc:

protoc \
	-I . \
	-I `go list -m -f {{.Dir}} github.com/alta/protopatch` \
	-I `go list -m -f {{.Dir}} google.golang.org/protobuf` \
	--go-patch_out=plugin=go,paths=source_relative:. \
	--go-patch_out=plugin=go-grpc,paths=source_relative:. \
	*.proto

Features

Patches are defined via an Options extension on messages, fields, oneof fields, enums, and enum values.

• go.message — message options, which modify the generated Go struct for a message.
• go.field — message field options, which modify Go struct fields and getter methods.
• go.oneof — oneof field options, which modify struct fields, interface types, and wrapper types.
• go.enum — enum options, which modify Go enum types and values.
• go.value — enum value options, which modify Go const values.

Custom Names

import "patch/go.proto";

message OldName {
	option (go.message).name = 'NewName';
	int id = 1 [(go.field).name = 'ID'];
}

enum Error {
	option (go.enum).name = 'ProtocolError';
	INVALID = 1 [(go.value).name = 'ErrInvalid'];
	NOT_FOUND = 2 [(go.value).name = 'ErrNotFound'];
	TOO_FUN = 3 [(go.value).name = 'ErrTooFun'];
}

Alternate Syntax

Multiple options can be grouped together with a message bounded by {}:

import "patch/go.proto";

message OldName {
	option (go.message) = {name: 'NewName'};
	int32 id = 1 [(go.field) = {name: 'ID'}];
}

enum Error {
	option (go.enum) = {name: 'ProtocolError'};
	INVALID = 1 [(go.value) = {name: 'ErrInvalid'}];
	NOT_FOUND = 2 [(go.value) = {name: 'ErrNotFound'}];
	TOO_FUN = 3 [(go.value) = {name: 'ErrTooFun'}];
}

Struct Tags

message ToDo {
	int32 id = 1 [(go.field).name: 'ID', (go.field).tags = 'xml:"id,attr"'];
	string description = 2 [(go.field).tags: 'xml:"desc"'];
}

Alternate Syntax

Multiple options can be grouped together with a message bounded by {}:

message ToDo {
	int32 id = 1 [(go.field) = {name: 'ID', tags: 'xml:"id,attr"'}];
	string description = 2 [(go.field) = {tags: 'xml:"desc"'}];
}

Embedded Fields

A message field can be embedded in the generated Go struct with the (go.field).embed option. This only works for message fields, and will not work for oneof fields or basic types.

import "patch/go.proto";

message A {
	B b = 1 [(go.field).embed = true];
}

message B {
	string value = 1;
}

The resulting Go struct will partially have the form:

type A struct {
	*B
}

type B struct {
	Value string
}

var a A
a.Value = "value" // This works because B is embedded in A

Alternate Syntax

Multiple options can be grouped together with a message bounded by {}:

import "patch/go.proto";

message A {
	B b = 1 [(go.field) = {embed: true}];
}

message B {
	string value = 1;
}

Linting

Protopatch can automatically “lint” generated names into something resembling idiomatic Go style. This feature should be considered unstable, and the names it generates are subject to change as this feature evolves.

• Initialisms: names with ID or URL or other well-known initialisms will have their case preserved. For example Id would lint to ID, and ApiBaseUrl would lint to APIBaseURL.
• Stuttering: it will attempt to remove repeated prefixed names from enum values. An enum value of type Foo named Foo_FOO_BAR would lint to FooBar.

To lint all generated Go names, add option (go.lint).all = true to your proto file. To lint only enum values, add option (go.lint).values = true. To specify one or more custom initialisms, specify an initialism with option (go.lint).initialisms = 'HSV' for the HSV initialism. All names with HSV will preserve its case.

option (go.lint).all = true;
option (go.lint).initialisms = 'RGB';
option (go.lint).initialisms = 'RGBA';
option (go.lint).initialisms = 'HSV';

enum Protocol {
	// PROTOCOL_INVALID value should lint to ProtocolInvalid.
	PROTOCOL_INVALID = 0;
	// PROTOCOL_IP value should lint to ProtocolIP.
	PROTOCOL_IP = 1;
	// PROTOCOL_UDP value should lint to ProtocolUDP.
	PROTOCOL_UDP = 2;
	// PROTOCOL_TCP value should lint to ProtocolTCP.
	PROTOCOL_TCP = 3;
}

message Color {
	oneof value {
		// rgb should lint to RGB.
		string rgb = 1;
		// rgba should lint to RGBA.
		string rgba = 2;
		// hsv should lint to HSV.
		string hsv = 3;
	}
}