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// extract-changelog extracts the release notes for a specific version from a
// file matching the format prescribed by https://keepachangelog.com/en/1.0.0/.
package main
import (
"bufio"
"bytes"
"errors"
"flag"
"fmt"
"io"
"os"
"strings"
)
func main() {
cmd := mainCmd{
Stdout: os.Stdout,
Stderr: os.Stderr,
}
if err := cmd.Run(os.Args[1:]); err != nil && err != flag.ErrHelp {
fmt.Fprintln(cmd.Stderr, err)
os.Exit(1)
}
}
type mainCmd struct {
Stdout io.Writer
Stderr io.Writer
}
const _usage = `USAGE
%v [OPTIONS] VERSION
Retrieves the release notes for VERSION from a CHANGELOG.md file and prints
them to stdout.
EXAMPLES
extract-changelog -i CHANGELOG.md v1.2.3
extract-changelog 0.2.5
OPTIONS
`
func (cmd *mainCmd) Run(args []string) error {
flag := flag.NewFlagSet("extract-changelog", flag.ContinueOnError)
flag.SetOutput(cmd.Stderr)
flag.Usage = func() {
fmt.Fprintf(flag.Output(), _usage, flag.Name())
flag.PrintDefaults()
}
file := flag.String("i", "CHANGELOG.md", "input file")
if err := flag.Parse(args); err != nil {
return err
}
var version string
if args := flag.Args(); len(args) > 0 {
version = args[0]
}
version = strings.TrimPrefix(version, "v")
if len(version) == 0 {
return errors.New("please provide a version")
}
f, err := os.Open(*file)
if err != nil {
return fmt.Errorf("open changelog: %v", err)
}
defer f.Close()
s, err := extract(f, version)
if err != nil {
return err
}
_, err = io.WriteString(cmd.Stdout, s)
return err
}
func extract(r io.Reader, version string) (string, error) {
type _state int
const (
initial _state = iota
foundHeader
)
var (
state _state
buff bytes.Buffer
scanner = bufio.NewScanner(r)
)
scan:
for scanner.Scan() {
line := scanner.Text()
switch state {
case initial:
// Version headers take one of the following forms:
//
// ## 0.1.3 - 2021-08-18
// ## [0.1.3] - 2021-08-18
switch {
case strings.HasPrefix(line, "## "+version+" "),
strings.HasPrefix(line, "## ["+version+"]"):
fmt.Fprintln(&buff, line)
state = foundHeader
}
case foundHeader:
// Found a new version header. Stop extracting.
if strings.HasPrefix(line, "## ") {
break scan
}
fmt.Fprintln(&buff, line)
default:
// unreachable but guard against it.
return "", fmt.Errorf("unexpected state %v at %q", state, line)
}
}
if err := scanner.Err(); err != nil {
return "", err
}
if state < foundHeader {
return "", fmt.Errorf("changelog for %q not found", version)
}
out := buff.String()
out = strings.TrimSpace(out) + "\n" // always end with a single newline
return out, nil
}
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