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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.
// Stringer is a tool to automate the creation of methods that satisfy the fmt.Stringer
// interface. 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
// 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.
//
// Stringer works best with constants that are consecutive values such as created using iota,
// but creates good code regardless. In the future it might also provide custom support for
// constant sets that are bit patterns.
//
// For example, given this snippet,
//
// package painkiller
//
// type Pill int
//
// const (
// Placebo Pill = iota
// Aspirin
// Ibuprofen
// Paracetamol
// Acetaminophen = Paracetamol
// )
//
// running this command
//
// stringer -type=Pill
//
// in the same directory will create the file pill_string.go, in package painkiller,
// containing a definition of
//
// func (Pill) String() string
//
// 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. It can be overridden
// with the -output flag.
//
package main // import "golang.org/x/tools/cmd/stringer"
import (
"bytes"
"flag"
"fmt"
"go/ast"
"go/build"
"go/constant"
"go/format"
"go/parser"
"go/token"
"go/types"
"io/ioutil"
"log"
"os"
"path/filepath"
"sort"
"strings"
)
var (
typeNames = flag.String("type", "", "comma-separated list of type names; must be set")
output = flag.String("output", "", "output file name; default srcdir/<type>_string.go")
trimprefix = flag.String("trimprefix", "", "trim the `prefix` from the generated constant names")
linecomment = flag.Bool("linecomment", false, "use line comment text as printed text when present")
buildTags = flag.String("tags", "", "comma-separated list of build tags to apply")
)
// Usage is a replacement usage function for the flags package.
func Usage() {
fmt.Fprintf(os.Stderr, "Usage of %s:\n", os.Args[0])
fmt.Fprintf(os.Stderr, "\tstringer [flags] -type T [directory]\n")
fmt.Fprintf(os.Stderr, "\tstringer [flags] -type T files... # Must be a single package\n")
fmt.Fprintf(os.Stderr, "For more information, see:\n")
fmt.Fprintf(os.Stderr, "\thttp://godoc.org/golang.org/x/tools/cmd/stringer\n")
fmt.Fprintf(os.Stderr, "Flags:\n")
flag.PrintDefaults()
}
func main() {
log.SetFlags(0)
log.SetPrefix("stringer: ")
flag.Usage = Usage
flag.Parse()
if len(*typeNames) == 0 {
flag.Usage()
os.Exit(2)
}
types := strings.Split(*typeNames, ",")
var tags []string
if len(*buildTags) > 0 {
tags = strings.Split(*buildTags, ",")
}
// We accept either one directory or a list of files. Which do we have?
args := flag.Args()
if len(args) == 0 {
// Default: process whole package in current directory.
args = []string{"."}
}
// Parse the package once.
var dir string
g := Generator{
trimPrefix: *trimprefix,
lineComment: *linecomment,
}
if len(args) == 1 && isDirectory(args[0]) {
dir = args[0]
g.parsePackageDir(args[0], tags)
} else {
if len(tags) != 0 {
log.Fatal("-tags option applies only to directories, not when files are specified")
}
dir = filepath.Dir(args[0])
g.parsePackageFiles(args)
}
// Print the header and package clause.
g.Printf("// Code generated by \"stringer %s\"; DO NOT EDIT.\n", strings.Join(os.Args[1:], " "))
g.Printf("\n")
g.Printf("package %s", g.pkg.name)
g.Printf("\n")
g.Printf("import \"strconv\"\n") // Used by all methods.
// Run generate for each type.
for _, typeName := range types {
g.generate(typeName)
}
// Format the output.
src := g.format()
// Write to file.
outputName := *output
if outputName == "" {
baseName := fmt.Sprintf("%s_string.go", types[0])
outputName = filepath.Join(dir, strings.ToLower(baseName))
}
err := ioutil.WriteFile(outputName, src, 0644)
if err != nil {
log.Fatalf("writing output: %s", err)
}
}
// isDirectory reports whether the named file is a directory.
func isDirectory(name string) bool {
info, err := os.Stat(name)
if err != nil {
log.Fatal(err)
}
return info.IsDir()
}
// Generator holds the state of the analysis. Primarily used to buffer
// the output for format.Source.
type Generator struct {
buf bytes.Buffer // Accumulated output.
pkg *Package // Package we are scanning.
trimPrefix string
lineComment bool
}
func (g *Generator) Printf(format string, args ...interface{}) {
fmt.Fprintf(&g.buf, format, args...)
}
// File holds a single parsed file and associated data.
type File struct {
pkg *Package // Package to which this file belongs.
file *ast.File // Parsed AST.
// These fields are reset for each type being generated.
typeName string // Name of the constant type.
values []Value // Accumulator for constant values of that type.
trimPrefix string
lineComment bool
}
type Package struct {
dir string
name string
defs map[*ast.Ident]types.Object
files []*File
typesPkg *types.Package
}
func buildContext(tags []string) *build.Context {
ctx := build.Default
ctx.BuildTags = tags
return &ctx
}
// parsePackageDir parses the package residing in the directory.
func (g *Generator) parsePackageDir(directory string, tags []string) {
pkg, err := buildContext(tags).ImportDir(directory, 0)
if err != nil {
log.Fatalf("cannot process directory %s: %s", directory, err)
}
var names []string
names = append(names, pkg.GoFiles...)
names = append(names, pkg.CgoFiles...)
// TODO: Need to think about constants in test files. Maybe write type_string_test.go
// in a separate pass? For later.
// names = append(names, pkg.TestGoFiles...) // These are also in the "foo" package.
names = append(names, pkg.SFiles...)
names = prefixDirectory(directory, names)
g.parsePackage(directory, names, nil)
}
// parsePackageFiles parses the package occupying the named files.
func (g *Generator) parsePackageFiles(names []string) {
g.parsePackage(".", names, nil)
}
// prefixDirectory places the directory name on the beginning of each name in the list.
func prefixDirectory(directory string, names []string) []string {
if directory == "." {
return names
}
ret := make([]string, len(names))
for i, name := range names {
ret[i] = filepath.Join(directory, name)
}
return ret
}
// parsePackage analyzes the single package constructed from the named files.
// If text is non-nil, it is a string to be used instead of the content of the file,
// to be used for testing. parsePackage exits if there is an error.
func (g *Generator) parsePackage(directory string, names []string, text interface{}) {
var files []*File
var astFiles []*ast.File
g.pkg = new(Package)
fs := token.NewFileSet()
for _, name := range names {
if !strings.HasSuffix(name, ".go") {
continue
}
parsedFile, err := parser.ParseFile(fs, name, text, parser.ParseComments)
if err != nil {
log.Fatalf("parsing package: %s: %s", name, err)
}
astFiles = append(astFiles, parsedFile)
files = append(files, &File{
file: parsedFile,
pkg: g.pkg,
trimPrefix: g.trimPrefix,
lineComment: g.lineComment,
})
}
if len(astFiles) == 0 {
log.Fatalf("%s: no buildable Go files", directory)
}
g.pkg.name = astFiles[0].Name.Name
g.pkg.files = files
g.pkg.dir = directory
g.pkg.typeCheck(fs, astFiles)
}
// check type-checks the package so we can evaluate contants whose values we are printing.
func (pkg *Package) typeCheck(fs *token.FileSet, astFiles []*ast.File) {
pkg.defs = make(map[*ast.Ident]types.Object)
config := types.Config{
IgnoreFuncBodies: true, // We only need to evaluate constants.
Importer: defaultImporter(),
FakeImportC: true,
}
info := &types.Info{
Defs: pkg.defs,
}
typesPkg, err := config.Check(pkg.dir, fs, astFiles, info)
if err != nil {
log.Fatalf("checking package: %s", err)
}
pkg.typesPkg = typesPkg
}
// generate produces the String method for the named type.
func (g *Generator) generate(typeName string) {
values := make([]Value, 0, 100)
for _, file := range g.pkg.files {
// Set the state for this run of the walker.
file.typeName = typeName
file.values = nil
if file.file != nil {
ast.Inspect(file.file, file.genDecl)
values = append(values, file.values...)
}
}
if len(values) == 0 {
log.Fatalf("no values defined for type %s", typeName)
}
runs := splitIntoRuns(values)
// The decision of which pattern to use depends on the number of
// runs in the numbers. If there's only one, it's easy. For more than
// one, there's a tradeoff between complexity and size of the data
// and code vs. the simplicity of a map. A map takes more space,
// but so does the code. The decision here (crossover at 10) is
// arbitrary, but considers that for large numbers of runs the cost
// of the linear scan in the switch might become important, and
// rather than use yet another algorithm such as binary search,
// we punt and use a map. In any case, the likelihood of a map
// being necessary for any realistic example other than bitmasks
// is very low. And bitmasks probably deserve their own analysis,
// to be done some other day.
switch {
case len(runs) == 1:
g.buildOneRun(runs, typeName)
case len(runs) <= 10:
g.buildMultipleRuns(runs, typeName)
default:
g.buildMap(runs, typeName)
}
}
// splitIntoRuns breaks the values into runs of contiguous sequences.
// For example, given 1,2,3,5,6,7 it returns {1,2,3},{5,6,7}.
// The input slice is known to be non-empty.
func splitIntoRuns(values []Value) [][]Value {
// We use stable sort so the lexically first name is chosen for equal elements.
sort.Stable(byValue(values))
// Remove duplicates. Stable sort has put the one we want to print first,
// so use that one. The String method won't care about which named constant
// was the argument, so the first name for the given value is the only one to keep.
// We need to do this because identical values would cause the switch or map
// to fail to compile.
j := 1
for i := 1; i < len(values); i++ {
if values[i].value != values[i-1].value {
values[j] = values[i]
j++
}
}
values = values[:j]
runs := make([][]Value, 0, 10)
for len(values) > 0 {
// One contiguous sequence per outer loop.
i := 1
for i < len(values) && values[i].value == values[i-1].value+1 {
i++
}
runs = append(runs, values[:i])
values = values[i:]
}
return runs
}
// format returns the gofmt-ed contents of the Generator's buffer.
func (g *Generator) format() []byte {
src, err := format.Source(g.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")
return g.buf.Bytes()
}
return src
}
// Value represents a declared constant.
type Value struct {
name string // The name of the constant.
// The value is stored as a bit pattern alone. The boolean tells us
// whether to interpret it as an int64 or a uint64; the only place
// this matters is when sorting.
// Much of the time the str field is all we need; it is printed
// by Value.String.
value uint64 // Will be converted to int64 when needed.
signed bool // Whether the constant is a signed type.
str string // The string representation given by the "go/constant" package.
}
func (v *Value) String() string {
return v.str
}
// byValue lets us sort the constants into increasing order.
// We take care in the Less method to sort in signed or unsigned order,
// as appropriate.
type byValue []Value
func (b byValue) Len() int { return len(b) }
func (b byValue) Swap(i, j int) { b[i], b[j] = b[j], b[i] }
func (b byValue) Less(i, j int) bool {
if b[i].signed {
return int64(b[i].value) < int64(b[j].value)
}
return b[i].value < b[j].value
}
// genDecl processes one declaration clause.
func (f *File) genDecl(node ast.Node) bool {
decl, ok := node.(*ast.GenDecl)
if !ok || decl.Tok != token.CONST {
// We only care about const declarations.
return true
}
// The name of the type of the constants we are declaring.
// Can change if this is a multi-element declaration.
typ := ""
// Loop over the elements of the declaration. Each element is a ValueSpec:
// a list of names possibly followed by a type, possibly followed by values.
// If the type and value are both missing, we carry down the type (and value,
// but the "go/types" package takes care of that).
for _, spec := range decl.Specs {
vspec := spec.(*ast.ValueSpec) // Guaranteed to succeed as this is CONST.
if vspec.Type == nil && len(vspec.Values) > 0 {
// "X = 1". With no type but a value, the constant is untyped.
// Skip this vspec and reset the remembered type.
typ = ""
continue
}
if vspec.Type != nil {
// "X T". We have a type. Remember it.
ident, ok := vspec.Type.(*ast.Ident)
if !ok {
continue
}
typ = ident.Name
}
if typ != f.typeName {
// This is not the type we're looking for.
continue
}
// We now have a list of names (from one line of source code) all being
// declared with the desired type.
// Grab their names and actual values and store them in f.values.
for _, name := range vspec.Names {
if name.Name == "_" {
continue
}
// This dance lets the type checker find the values for us. It's a
// bit tricky: look up the object declared by the name, find its
// types.Const, and extract its value.
obj, ok := f.pkg.defs[name]
if !ok {
log.Fatalf("no value for constant %s", name)
}
info := obj.Type().Underlying().(*types.Basic).Info()
if info&types.IsInteger == 0 {
log.Fatalf("can't handle non-integer constant type %s", typ)
}
value := obj.(*types.Const).Val() // Guaranteed to succeed as this is CONST.
if value.Kind() != constant.Int {
log.Fatalf("can't happen: constant is not an integer %s", name)
}
i64, isInt := constant.Int64Val(value)
u64, isUint := constant.Uint64Val(value)
if !isInt && !isUint {
log.Fatalf("internal error: value of %s is not an integer: %s", name, value.String())
}
if !isInt {
u64 = uint64(i64)
}
v := Value{
name: name.Name,
value: u64,
signed: info&types.IsUnsigned == 0,
str: value.String(),
}
if c := vspec.Comment; f.lineComment && c != nil && len(c.List) == 1 {
v.name = strings.TrimSpace(c.Text())
}
v.name = strings.TrimPrefix(v.name, f.trimPrefix)
f.values = append(f.values, v)
}
}
return false
}
// Helpers
// usize returns the number of bits of the smallest unsigned integer
// type that will hold n. Used to create the smallest possible slice of
// integers to use as indexes into the concatenated strings.
func usize(n int) int {
switch {
case n < 1<<8:
return 8
case n < 1<<16:
return 16
default:
// 2^32 is enough constants for anyone.
return 32
}
}
// declareIndexAndNameVars declares the index slices and concatenated names
// strings representing the runs of values.
func (g *Generator) declareIndexAndNameVars(runs [][]Value, typeName string) {
var indexes, names []string
for i, run := range runs {
index, name := g.createIndexAndNameDecl(run, typeName, fmt.Sprintf("_%d", i))
if len(run) != 1 {
indexes = append(indexes, index)
}
names = append(names, name)
}
g.Printf("const (\n")
for _, name := range names {
g.Printf("\t%s\n", name)
}
g.Printf(")\n\n")
if len(indexes) > 0 {
g.Printf("var (")
for _, index := range indexes {
g.Printf("\t%s\n", index)
}
g.Printf(")\n\n")
}
}
// declareIndexAndNameVar is the single-run version of declareIndexAndNameVars
func (g *Generator) declareIndexAndNameVar(run []Value, typeName string) {
index, name := g.createIndexAndNameDecl(run, typeName, "")
g.Printf("const %s\n", name)
g.Printf("var %s\n", index)
}
// createIndexAndNameDecl returns the pair of declarations for the run. The caller will add "const" and "var".
func (g *Generator) createIndexAndNameDecl(run []Value, typeName string, suffix string) (string, string) {
b := new(bytes.Buffer)
indexes := make([]int, len(run))
for i := range run {
b.WriteString(run[i].name)
indexes[i] = b.Len()
}
nameConst := fmt.Sprintf("_%s_name%s = %q", typeName, suffix, b.String())
nameLen := b.Len()
b.Reset()
fmt.Fprintf(b, "_%s_index%s = [...]uint%d{0, ", typeName, suffix, usize(nameLen))
for i, v := range indexes {
if i > 0 {
fmt.Fprintf(b, ", ")
}
fmt.Fprintf(b, "%d", v)
}
fmt.Fprintf(b, "}")
return b.String(), nameConst
}
// declareNameVars declares the concatenated names string representing all the values in the runs.
func (g *Generator) declareNameVars(runs [][]Value, typeName string, suffix string) {
g.Printf("const _%s_name%s = \"", typeName, suffix)
for _, run := range runs {
for i := range run {
g.Printf("%s", run[i].name)
}
}
g.Printf("\"\n")
}
// buildOneRun generates the variables and String method for a single run of contiguous values.
func (g *Generator) buildOneRun(runs [][]Value, typeName string) {
values := runs[0]
g.Printf("\n")
g.declareIndexAndNameVar(values, typeName)
// The generated code is simple enough to write as a Printf format.
lessThanZero := ""
if values[0].signed {
lessThanZero = "i < 0 || "
}
if values[0].value == 0 { // Signed or unsigned, 0 is still 0.
g.Printf(stringOneRun, typeName, usize(len(values)), lessThanZero)
} else {
g.Printf(stringOneRunWithOffset, typeName, values[0].String(), usize(len(values)), lessThanZero)
}
}
// Arguments to format are:
// [1]: type name
// [2]: size of index element (8 for uint8 etc.)
// [3]: less than zero check (for signed types)
const stringOneRun = `func (i %[1]s) String() string {
if %[3]si >= %[1]s(len(_%[1]s_index)-1) {
return "%[1]s(" + strconv.FormatInt(int64(i), 10) + ")"
}
return _%[1]s_name[_%[1]s_index[i]:_%[1]s_index[i+1]]
}
`
// Arguments to format are:
// [1]: type name
// [2]: lowest defined value for type, as a string
// [3]: size of index element (8 for uint8 etc.)
// [4]: less than zero check (for signed types)
/*
*/
const stringOneRunWithOffset = `func (i %[1]s) String() string {
i -= %[2]s
if %[4]si >= %[1]s(len(_%[1]s_index)-1) {
return "%[1]s(" + strconv.FormatInt(int64(i + %[2]s), 10) + ")"
}
return _%[1]s_name[_%[1]s_index[i] : _%[1]s_index[i+1]]
}
`
// buildMultipleRuns generates the variables and String method for multiple runs of contiguous values.
// For this pattern, a single Printf format won't do.
func (g *Generator) buildMultipleRuns(runs [][]Value, typeName string) {
g.Printf("\n")
g.declareIndexAndNameVars(runs, typeName)
g.Printf("func (i %s) String() string {\n", typeName)
g.Printf("\tswitch {\n")
for i, values := range runs {
if len(values) == 1 {
g.Printf("\tcase i == %s:\n", &values[0])
g.Printf("\t\treturn _%s_name_%d\n", typeName, i)
continue
}
g.Printf("\tcase %s <= i && i <= %s:\n", &values[0], &values[len(values)-1])
if values[0].value != 0 {
g.Printf("\t\ti -= %s\n", &values[0])
}
g.Printf("\t\treturn _%s_name_%d[_%s_index_%d[i]:_%s_index_%d[i+1]]\n",
typeName, i, typeName, i, typeName, i)
}
g.Printf("\tdefault:\n")
g.Printf("\t\treturn \"%s(\" + strconv.FormatInt(int64(i), 10) + \")\"\n", typeName)
g.Printf("\t}\n")
g.Printf("}\n")
}
// buildMap handles the case where the space is so sparse a map is a reasonable fallback.
// It's a rare situation but has simple code.
func (g *Generator) buildMap(runs [][]Value, typeName string) {
g.Printf("\n")
g.declareNameVars(runs, typeName, "")
g.Printf("\nvar _%s_map = map[%s]string{\n", typeName, typeName)
n := 0
for _, values := range runs {
for _, value := range values {
g.Printf("\t%s: _%s_name[%d:%d],\n", &value, typeName, n, n+len(value.name))
n += len(value.name)
}
}
g.Printf("}\n\n")
g.Printf(stringMap, typeName)
}
// Argument to format is the type name.
const stringMap = `func (i %[1]s) String() string {
if str, ok := _%[1]s_map[i]; ok {
return str
}
return "%[1]s(" + strconv.FormatInt(int64(i), 10) + ")"
}
`