Add new protoc-gen-alias command to allow backwards version compat

cmd/protoc-gen-alias/Makefile

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+test: build
+	cd test && make clean test
+
+build:
+	go install .

cmd/protoc-gen-alias/README.md

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+# protoc-gen-alias
+
+`protoc-gen-alias` is a plugin for protoc which type alias for all messages, such that one protobuf definition can
+be consumed from many Go packages
+
+## Usage
+
+Usage is typically through `buf`, but you can use directly.
+See `test/Makefile` for example usage.
+
+## Configuration
+
+The plugin looks for a comment like `+cue-gen:Simple:versions:v1,v1alpha` on the package.
+This will generate aliases to the current version, for all versions listed (the current version is ignored).
+
+## Examples Of Generated Code
+
+```go
+// Code generated by protoc-gen-jsonshim. DO NOT EDIT.
+type Simple = v1.Simple
+type Simple_Name = v1.Simple_Name
+type Simple_Number = v1.Simple_Number
+type SimpleWithMap = v1.SimpleWithMap
+type SimpleWithMap_Nested = v1.SimpleWithMap_Nested
+type ReferencedMap = v1.ReferencedMap
+type ImportedReference = v1.ImportedReference
+```

cmd/protoc-gen-alias/main.go

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+// Copyright 2019 Istio Authors
+//
+//   Licensed 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 main
+
+import (
+	"path/filepath"
+	"strings"
+
+	"google.golang.org/protobuf/compiler/protogen"
+	"google.golang.org/protobuf/types/descriptorpb"
+)
+
+func main() {
+	protogen.Options{}.Run(func(gen *protogen.Plugin) error {
+		for _, f := range gen.Files {
+			if !f.Generate {
+				continue
+			}
+			generateFile(gen, f)
+		}
+		return nil
+	})
+}
+
+func generateFile(gen *protogen.Plugin, file *protogen.File) {
+	ourVersion := filepath.Base(filepath.Dir(file.Desc.Path()))
+	var versions []string
+	for _, msg := range file.Messages {
+		for _, line := range strings.Split(msg.Comments.Leading.String(), "\n") {
+			// Looking for something like '// +cue-gen:Simple:versions:v1,v1alpha'
+			if strings.HasPrefix(line, "// +cue-gen:") {
+				items := strings.Split(line, ":")
+				if len(items) != 4 {
+					continue
+				}
+				if items[2] == "versions" {
+					for _, v := range strings.Split(items[3], ",") {
+						if v != ourVersion {
+							versions = append(versions, v)
+						}
+					}
+				}
+			}
+		}
+	}
+	if len(versions) == 0 {
+		return
+	}
+	base := filepath.Dir(filepath.Dir(file.Desc.Path()))
+	fnamePrefix := filepath.Base(file.GeneratedFilenamePrefix)
+	for _, aliasVersion := range versions {
+		filename := filepath.Join(base, aliasVersion, fnamePrefix+"_alias.gen.go")
+		p := gen.NewGeneratedFile(filename, file.GoImportPath)
+
+		p.P("// Code generated by protoc-gen-alias. DO NOT EDIT.")
+		p.P("package ", aliasVersion)
+		p.P(`import `, file.GoImportPath)
+		var processMessages func([]*protogen.Message)
+		var processEnums func([]*protogen.Enum)
+		var processOneofs func([]*protogen.Oneof)
+
+		processEnums = func(enums []*protogen.Enum) {
+			for _, e := range enums {
+				typeName := e.GoIdent.GoName
+				p.P(`type `, typeName, `= `, file.GoPackageName, ".", e.GoIdent)
+				for _, v := range e.Values {
+					p.P(`const `, v.GoIdent, " ", typeName, `= `, file.GoPackageName, ".", v.GoIdent)
+				}
+			}
+		}
+		processOneofs = func(oneofs []*protogen.Oneof) {
+			for _, e := range oneofs {
+				for _, f := range e.Fields {
+					p.P(`type `, f.GoIdent, `= `, file.GoPackageName, ".", f.GoIdent)
+				}
+			}
+		}
+		processMessages = func(messages []*protogen.Message) {
+			for _, message := range messages {
+				// skip maps in protos.
+				if message.Desc.Options().(*descriptorpb.MessageOptions).GetMapEntry() {
+					continue
+				}
+				typeName := message.GoIdent.GoName
+				p.P(`type `, typeName, "= ", file.GoPackageName, ".", message.GoIdent)
+				processMessages(message.Messages)
+				processEnums(message.Enums)
+				processOneofs(message.Oneofs)
+			}
+		}
+		processMessages(file.Messages)
+		processEnums(file.Enums)
+
+	}
+}

cmd/protoc-gen-alias/test/Makefile

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+
+go_package = istio.io/tools/cmd/protoc-gen-golang-jsonshim/test/generated
+
+all: clean test
+
+clean:
+	if [ -d "generated" ]; then rm -rf generated; fi
+
+test: generate gobuild gotest
+
+generate:
+	if [ ! -d "generated" ]; then mkdir generated; fi
+	protoc --go_out=. --go_opt=paths=source_relative \
+		   --alias_out=. --alias_opt=paths=source_relative \
+		   v1/*.proto
+
+gobuild:
+	go build ./...
+
+gotest:
+	go test .

cmd/protoc-gen-alias/test/alias_test.go

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+// Copyright 2019 Istio Authors
+//
+//   Licensed 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 test
+
+import (
+	"testing"
+
+	"google.golang.org/protobuf/proto"
+
+	v1 "istio.io/tools/cmd/protoc-gen-alias/test/v1"
+	"istio.io/tools/cmd/protoc-gen-alias/test/v1alpha"
+)
+
+func TestSimpleCase(t *testing.T) {
+	concrete := &v1.Simple{
+		FieldA: 1,
+		FieldB: "test",
+		FieldC: &v1.Simple_Name{
+			Name: "test",
+		},
+	}
+	alias := &v1alpha.Simple{
+		FieldA: 1,
+		FieldB: "test",
+		FieldC: &v1alpha.Simple_Name{
+			Name: "test",
+		},
+	}
+	mixedAliasFirst := &v1alpha.Simple{
+		FieldA: 1,
+		FieldB: "test",
+		FieldC: &v1.Simple_Name{
+			Name: "test",
+		},
+	}
+	mixedConcreteFirst := &v1.Simple{
+		FieldA: 1,
+		FieldB: "test",
+		FieldC: &v1alpha.Simple_Name{
+			Name: "test",
+		},
+	}
+	// Test we can do proto operations
+	proto.Equal(concrete, alias)
+	proto.Equal(concrete, mixedConcreteFirst)
+	proto.Equal(concrete, mixedAliasFirst)
+	if proto.MessageName(mixedConcreteFirst).Name() != "Simple" {
+		t.Errorf("proto name should be Simple")
+	}
+	if proto.MessageName(mixedAliasFirst).Name() != "Simple" {
+		t.Errorf("proto name should be Simple")
+	}
+}