go dns breaking change sketch

breaking_generate.go

// +build ignore

package main

import (
	"bytes"
	"fmt"
	"os"
	"os/exec"
)

func Must(a ...interface{}) {
	switch err := a[len(a)-1].(type) {
	case nil:
	case error:
		panic(err)
	default:
		panic("unreachable")
	}
}

func main() {
	// Note: hash_start depends on prettyfmt
	prettyfmt := `%w(0)
    %h %cd %s

    Commit: https://github.com/miekg/dns/commit/%h
    Issues: https://github.com/miekg/dns/search?q=%h&type=Issues

    %w(72,0,4)%b%w(0)

`
	hash_start := 5
	cmd := exec.Command("git", "log", "--grep=#breaking", "--date=short", "--pretty="+prettyfmt)
	var buf bytes.Buffer
	cmd.Stdout = &buf
	Must(cmd.Run())
	stdout := buf.Bytes()
	file, err := os.Create("zbreaking.go")
	Must(err)
	Must(fmt.Fprint(file, "//go:generate go run breaking_generate.go\n\n"))
	if len(stdout) == 0 {
		Must(fmt.Fprint(file, "package dns\n"))
		return
	}
	Must(fmt.Fprintf(file, `/*
Breaking Changes

On rare occasions a breaking change may be introduced to fix a bug or flaw.
As of 22 February 2016 commits introducing breaking changes are tagged
#breaking and the commit hash of the the last breaking change is exported
as the constant LastBreakingChange.

Full list of breaking commits:

%s
*/
package dns

// LastBreakingChange is the short hash of the commit that introduced the last breaking change.
const LastBreakingChange string = "%s"
`, stdout, stdout[hash_start:hash_start+7]))
}

zbreaking.go

//go:generate go run breaking_generate.go

package dns

Idea #2: can't we specify some rewrite rules with gofmt that can be used to rewrite your repro when we have breaking changes?

(haven't looked at the above code yet)

The above looks nice. I wonder, if we should just hold up all breaking changes and then make one release that breaks. I mean just telling there are breaking changes is only one side of the equation.