StringToString usage output is unstable

[SOF3]

Since Go maps have randomized iteration order, FlagUsages() returns inconsistent output:

playground

// You can edit this code!
// Click here and start typing.
package main

import (
	"fmt"

	"github.com/spf13/pflag"
)

func main() {
	counter := map[string]int{}

	for i := 0; i < 100; i++ {
		fs := pflag.NewFlagSet("t", pflag.ExitOnError)
		fs.StringToString("foo", map[string]string{"a": "b", "c": "d"}, "usage")
		output := fs.FlagUsages()
		counter[output]++
	}

	fmt.Print(counter)
}

map[      --foo stringToString   usage (default [a=b,c=d])
:88       --foo stringToString   usage (default [c=d,a=b])
:12]

In projects with a workflow that writes the command usage to a file (e.g. README), this causes unnecessary diff all the time.

[twz123]

It's a general issue concerning reproducibility. If you want to create an OS package including docs, say, man pages, it won't be reproducible since the man pages will differ on each build.