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logger.go
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logger.go
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// Copyright 2022 Outreach Corporation. All Rights Reserved.
// main
//
// The logger cmd can be used to generate log marshalers for structs.
//
// # See generating.md for generating log marshalers
//
// Usage: logger [flag] [files]
//
// By default the output is written to marshalers.go
package main
import (
"bytes"
"flag"
"fmt"
"go/types"
"io"
"log"
"os"
"reflect"
"sort"
"strings"
"text/template"
"golang.org/x/tools/go/packages"
"golang.org/x/tools/imports"
)
// nolint:gochecknoglobals // Why: flag used in multiple places
var (
outputFile = flag.String("output", "marshalers.go", "location of generated marshalers")
header = `// Code generated by "logger %s"; DO NOT EDIT.
package %s
`
functionHeaderFormat = `
func (s *{{ .name }}) MarshalLog(addField func(key string, value interface{})) {
if s == nil {
return
}
`
timeFieldFormat = `
addField("{{.key}}", s.{{.name}}.UTC().Format(time.RFC3339Nano))`
simpleFieldFormat = `
addField("{{.key}}", s.{{.name}})`
nestedMarshalerFormat = `
s.{{.name}}.MarshalLog(addField)`
nestedNilableMarshalerFormat = `
if s.{{.name}} != nil {
s.{{.name}}.MarshalLog(addField)
}`
)
func main() {
flag.Usage = usage
flag.Parse()
args := flag.Args()
// use current directory if no file names are provided
if len(args) == 0 {
args = []string{"."}
}
mode := packages.NeedName | packages.NeedTypes | packages.NeedTypesInfo | packages.NeedImports | packages.NeedDeps
cfg := &packages.Config{Mode: mode, Tests: false}
pkgs, err := packages.Load(cfg, args...)
if err != nil || len(pkgs) != 1 {
log.Fatalf("generation failed %v", err)
}
scanPackage(pkgs[0])
}
func scanPackage(pkg *packages.Package) {
var buf bytes.Buffer
fmt.Fprintf(&buf, header, strings.Join(os.Args[1:], " "), pkg.Name)
names, structs := filterStructs(pkg)
for kk := range names {
processStruct(&buf, structs[kk], names[kk])
}
// run the equivalent of goimports -w
result, err := imports.Process(*outputFile, buf.Bytes(), nil)
if err != nil {
log.Fatal(err)
}
// write to stdout
if err := os.WriteFile(*outputFile, result, 0o600); err != nil {
log.Fatal(err)
}
}
func filterStructs(pkg *packages.Package) ([]string, []*types.Struct) {
names := []string{}
structs := map[string]*types.Struct{}
// look for structs which have the `log:".."` tag specified
for _, def := range pkg.TypesInfo.Defs {
typeName, ok := def.(*types.TypeName)
if !ok {
continue
}
s, ok := typeName.Type().Underlying().(*types.Struct)
if !ok {
continue
}
for kk := 0; kk < s.NumFields(); kk++ {
if _, ok := reflect.StructTag(s.Tag(kk)).Lookup("log"); ok {
structs[typeName.Name()] = s
names = append(names, typeName.Name())
break
}
}
}
sort.Strings(names)
result := make([]*types.Struct, len(names))
for kk, name := range names {
result[kk] = structs[name]
}
return names, result
}
func processStruct(w io.Writer, s *types.Struct, name string) {
write(w, functionHeaderFormat, map[string]string{"name": name})
for kk := 0; kk < s.NumFields(); kk++ {
if field, ok := reflect.StructTag(s.Tag(kk)).Lookup("log"); ok {
args := map[string]string{"key": field, "name": s.Field(kk).Name()}
switch {
case s.Field(kk).Type().String() == "time.Time":
write(w, timeFieldFormat, args)
case field == "." && isNilable(s.Field(kk).Type()):
write(w, nestedNilableMarshalerFormat, args)
case field == ".":
write(w, nestedMarshalerFormat, args)
default:
write(w, simpleFieldFormat, args)
}
}
}
fmt.Fprintf(w, "\n}\n")
}
func isNilable(t types.Type) bool {
_, isInterface := t.Underlying().(*types.Interface)
_, isPointer := t.Underlying().(*types.Pointer)
return isInterface || isPointer
}
func write(w io.Writer, s string, args map[string]string) {
err := template.Must(template.New("tpl").Parse(s)).Execute(w, args)
if err != nil {
panic(err)
}
}
// usage is printed out automatically by flags when needed
func usage() {
fmt.Fprintf(os.Stderr, "Usage of logger:\n")
fmt.Fprintf(os.Stderr, "\tlogger [go files or directory]\n")
fmt.Fprintf(os.Stderr, "Flags:\n")
flag.PrintDefaults()
}