Add protoc-gen-go-fieldpath

This command will replace protobuf/plugin/fieldpath when we migrate
off from gogo/protobuf.

See containerd#6564 for the detail.

Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>

cmd/protoc-gen-go-fieldpath/generator.go

@@ -0,0 +1,155 @@
+/*
+   Copyright The containerd 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 (
+	"google.golang.org/protobuf/compiler/protogen"
+	"google.golang.org/protobuf/reflect/protoreflect"
+)
+
+type generator struct {
+	out *protogen.GeneratedFile
+}
+
+func newGenerator(out *protogen.GeneratedFile) *generator {
+	gen := generator{out: out}
+	return &gen
+}
+
+func (gen *generator) genFieldMethod(m *protogen.Message) {
+	p := gen.out
+
+	p.P("// Field returns the value for the given fieldpath as a string, if defined.")
+	p.P("// If the value is not defined, the second value will be false.")
+	p.P("func (m *", m.GoIdent, ") Field(fieldpath []string) (string, bool) {")
+
+	var (
+		fields    []*protogen.Field
+		unhandled []*protogen.Field
+	)
+
+	for _, f := range m.Fields {
+		if f.Desc.Kind() == protoreflect.BoolKind ||
+			f.Desc.Kind() == protoreflect.StringKind ||
+			isLabelsField(f) || isAnyField(f) || isMessageField(f) {
+			fields = append(fields, f)
+		} else {
+			unhandled = append(unhandled, f)
+		}
+
+	}
+
+	if len(fields) > 0 {
+		p.P("if len(fieldpath) == 0 {")
+		p.P(`return "", false`)
+		p.P("}")
+
+		p.P("switch fieldpath[0] {")
+
+		for _, f := range unhandled {
+			p.P("// unhandled: ", f.Desc.Name())
+		}
+
+		for _, f := range fields {
+			p.P(`case "`, f.Desc.Name(), `":`)
+			switch {
+			case isLabelsField(f):
+				stringsJoin := gen.out.QualifiedGoIdent(protogen.GoIdent{
+					GoImportPath: "strings",
+					GoName:       "Join",
+				})
+
+				p.P(`// Labels fields have been special-cased by name. If this breaks,`)
+				p.P(`// add better special casing to fieldpath plugin.`)
+				p.P("if len(m.", f.GoName, ") == 0 {")
+				p.P(`return "", false`)
+				p.P("}")
+				p.P("value, ok := m.", f.GoName, "[", stringsJoin, `(fieldpath[1:], ".")]`)
+				p.P("return value, ok")
+			case isAnyField(f):
+				typeurlUnmarshalAny := gen.out.QualifiedGoIdent(protogen.GoIdent{
+					GoImportPath: "github.com/containerd/typeurl",
+					GoName:       "UnmarshalAny",
+				})
+
+				p.P("decoded, err := ", typeurlUnmarshalAny, "(m.", f.GoName, ")")
+				p.P("if err != nil {")
+				p.P(`return "", false`)
+				p.P("}")
+				p.P("adaptor, ok := decoded.(interface{ Field([]string) (string, bool) })")
+				p.P("if !ok {")
+				p.P(`return "", false`)
+				p.P("}")
+				p.P("return adaptor.Field(fieldpath[1:])")
+			case isMessageField(f):
+				p.P(`// NOTE(stevvooe): This is probably not correct in many cases.`)
+				p.P(`// We assume that the target message also implements the Field`)
+				p.P(`// method, which isn't likely true in a lot of cases.`)
+				p.P(`//`)
+				p.P(`// If you have a broken build and have found this comment,`)
+				p.P(`// you may be closer to a solution.`)
+				p.P("if m.", f.GoName, " == nil {")
+				p.P(`return "", false`)
+				p.P("}")
+				p.P("return m.", f.GoName, ".Field(fieldpath[1:])")
+			case f.Desc.Kind() == protoreflect.StringKind:
+				p.P("return string(m.", f.GoName, "), len(m.", f.GoName, ") > 0")
+			case f.Desc.Kind() == protoreflect.BoolKind:
+				fmtSprint := gen.out.QualifiedGoIdent(protogen.GoIdent{
+					GoImportPath: "fmt",
+					GoName:       "Sprint",
+				})
+
+				p.P("return ", fmtSprint, "(m.", f.GoName, "), true")
+			}
+		}
+
+		p.P("}")
+	} else {
+		for _, f := range unhandled {
+			p.P("// unhandled: ", f.Desc.Name())
+		}
+	}
+
+	p.P(`return "", false`)
+	p.P("}")
+}
+
+func isMessageField(f *protogen.Field) bool {
+	return f.Desc.Kind() == protoreflect.MessageKind && f.GoIdent.GoName != "Timestamp"
+}
+
+func isLabelsField(f *protogen.Field) bool {
+	return f.Desc.Kind() == protoreflect.MessageKind && f.Desc.Name() == "labels"
+}
+
+func isAnyField(f *protogen.Field) bool {
+	return f.Desc.Kind() == protoreflect.MessageKind && f.GoIdent.GoName == "Any"
+}
+
+func generate(plugin *protogen.Plugin, input *protogen.File) error {
+	file := plugin.NewGeneratedFile(input.GeneratedFilenamePrefix+"_fieldpath.pb.go", input.GoImportPath)
+	file.P("// Code generated by protoc-gen-go-fieldpath. DO NOT EDIT.")
+	file.P("// source: ", input.Desc.Path())
+	file.P("package ", input.GoPackageName)
+
+	gen := newGenerator(file)
+	for _, m := range input.Messages {
+		gen.genFieldMethod(m)
+	}
+	return nil
+}

cmd/protoc-gen-go-fieldpath/main.go

@@ -0,0 +1,35 @@
+/*
+   Copyright The containerd 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 (
+	"google.golang.org/protobuf/compiler/protogen"
+)
+
+func main() {
+	protogen.Options{}.Run(func(gen *protogen.Plugin) error {
+		for _, f := range gen.Files {
+			if !f.Generate {
+				continue
+			}
+			if err := generate(gen, f); err != nil {
+				return err
+			}
+		}
+		return nil
+	})
+}