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jsonenums.go
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jsonenums.go
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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// JSONenums is a tool to automate the creation of methods that satisfy the
// fmt.Stringer, json.Marshaler and json.Unmarshaler interfaces.
// Given the name of a (signed or unsigned) integer type T that has constants
// defined, stringer will create a new self-contained Go source file implementing
//
// func (t T) String() string
// func (t T) MarshalJSON() ([]byte, error)
// func (t *T) UnmarshalJSON([]byte) error
//
// The file is created in the same package and directory as the package that defines T.
// It has helpful defaults designed for use with go generate.
//
// JSONenums is a simple implementation of a concept and the code might not be
// the most performant or beautiful to read.
//
// For example, given this snippet,
//
// package painkiller
//
// type Pill int
//
// const (
// Placebo Pill = iota
// Aspirin
// Ibuprofen
// Paracetamol
// Acetaminophen = Paracetamol
// )
//
// running this command
//
// jsonenums -type=Pill
//
// in the same directory will create the file pill_jsonenums.go, in package painkiller,
// containing a definition of
//
// func (r Pill) String() string
// func (r Pill) MarshalJSON() ([]byte, error)
// func (r *Pill) UnmarshalJSON([]byte) error
//
// That method will translate the value of a Pill constant to the string representation
// of the respective constant name, so that the call fmt.Print(painkiller.Aspirin) will
// print the string "Aspirin".
//
// Typically this process would be run using go generate, like this:
//
// //go:generate stringer -type=Pill
//
// If multiple constants have the same value, the lexically first matching name will
// be used (in the example, Acetaminophen will print as "Paracetamol").
//
// With no arguments, it processes the package in the current directory.
// Otherwise, the arguments must name a single directory holding a Go package
// or a set of Go source files that represent a single Go package.
//
// The -type flag accepts a comma-separated list of types so a single run can
// generate methods for multiple types. The default output file is t_string.go,
// where t is the lower-cased name of the first type listed. THe suffix can be
// overridden with the -suffix flag.
//
package main
import (
"bytes"
"flag"
"go/format"
"io/ioutil"
"log"
"os"
"path/filepath"
"strings"
"github.com/campoy/jsonenums/parser"
)
var (
typeNames = flag.String("type", "", "comma-separated list of type names; must be set")
outputSuffix = flag.String("suffix", "_jsonenums", "suffix to be added to the output file")
)
func main() {
flag.Parse()
if len(*typeNames) == 0 {
log.Fatalf("the flag -type must be set")
}
types := strings.Split(*typeNames, ",")
// Only one directory at a time can be processed, and the default is ".".
dir := "."
if args := flag.Args(); len(args) == 1 {
dir = args[0]
} else if len(args) > 1 {
log.Fatalf("only one directory at a time")
}
pkg, err := parser.ParsePackage(dir, *outputSuffix+".go")
if err != nil {
log.Fatalf("parsing package: %v", err)
}
var analysis = struct {
Command string
PackageName string
TypesAndValues map[string][]string
}{
Command: strings.Join(os.Args[1:], " "),
PackageName: pkg.Name,
TypesAndValues: make(map[string][]string),
}
// Run generate for each type.
for _, typeName := range types {
values, err := pkg.ValuesOfType(typeName)
if err != nil {
log.Fatalf("finding values for type %v: %v", typeName, err)
}
analysis.TypesAndValues[typeName] = values
var buf bytes.Buffer
if err := generatedTmpl.Execute(&buf, analysis); err != nil {
log.Fatalf("generating code: %v", err)
}
src, err := format.Source(buf.Bytes())
if err != nil {
// Should never happen, but can arise when developing this code.
// The user can compile the output to see the error.
log.Printf("warning: internal error: invalid Go generated: %s", err)
log.Printf("warning: compile the package to analyze the error")
src = buf.Bytes()
}
output := strings.ToLower(typeName + *outputSuffix + ".go")
outputPath := filepath.Join(dir, output)
if err := ioutil.WriteFile(outputPath, src, 0644); err != nil {
log.Fatalf("writing output: %s", err)
}
}
}