build-release-binaries: support building a subset of all platforms

helpers/build-release-binaries/main.go

@@ -1,11 +1,14 @@
 package main
 
 import (
+	"errors"
 	"fmt"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"runtime"
+	"sort"
+	"strconv"
 	"strings"
 	"time"
 
@@ -14,16 +17,18 @@ import (
 )
 
 var opts = struct {
-	Verbose   bool
-	SourceDir string
-	OutputDir string
-	Version   string
+	Verbose        bool
+	SourceDir      string
+	OutputDir      string
+	PlatformSubset string
+	Version        string
 }{}
 
 func init() {
 	pflag.BoolVarP(&opts.Verbose, "verbose", "v", false, "be verbose")
 	pflag.StringVarP(&opts.SourceDir, "source", "s", "/restic", "path to the source code `directory`")
 	pflag.StringVarP(&opts.OutputDir, "output", "o", "/output", "path to the output `directory`")
+	pflag.StringVar(&opts.PlatformSubset, "platform-subset", "", "specify `n/t` to only build this subset")
 	pflag.StringVar(&opts.Version, "version", "", "use `x.y.z` as the version for output files")
 	pflag.Parse()
 }
@@ -244,15 +249,69 @@ func downloadModules(sourceDir string) {
 	}
 }
 
+func selectSubset(subset string, target map[string][]string) (map[string][]string, error) {
+	t, n, _ := strings.Cut(subset, "/")
+	part, err := strconv.ParseInt(t, 10, 8)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse platform subset %q", subset)
+	}
+	total, err := strconv.ParseInt(n, 10, 8)
+	if err != nil {
+		return nil, fmt.Errorf("failed to parse platform subset %q", subset)
+	}
+	if total < 0 || part < 0 {
+		return nil, errors.New("platform subset out of range")
+	}
+	if part >= total {
+		return nil, errors.New("t must be in 0 <= t < n")
+	}
+
+	// flatten platform list
+	platforms := []string{}
+	for os, archs := range target {
+		for _, arch := range archs {
+			platforms = append(platforms, os+"/"+arch)
+		}
+	}
+	sort.Strings(platforms)
+
+	// select subset
+	lower := len(platforms) * int(part) / int(total)
+	upper := len(platforms) * int(part+1) / int(total)
+	platforms = platforms[lower:upper]
+
+	return buildPlatformList(platforms), nil
+}
+
+func buildPlatformList(platforms []string) map[string][]string {
+	fmt.Printf("Building for %v\n", platforms)
+
+	targets := make(map[string][]string)
+	for _, platform := range platforms {
+		os, arch, _ := strings.Cut(platform, "/")
+		targets[os] = append(targets[os], arch)
+	}
+	return targets
+}
+
 func main() {
 	if len(pflag.Args()) != 0 {
 		die("USAGE: build-release-binaries [OPTIONS]")
 	}
 
+	targets := defaultBuildTargets
+	if opts.PlatformSubset != "" {
+		var err error
+		targets, err = selectSubset(opts.PlatformSubset, targets)
+		if err != nil {
+			die("%s", err)
+		}
+	}
+
 	sourceDir := abs(opts.SourceDir)
 	outputDir := abs(opts.OutputDir)
 	mkdir(outputDir)
 
 	downloadModules(sourceDir)
-	buildTargets(sourceDir, outputDir, defaultBuildTargets)
+	buildTargets(sourceDir, outputDir, targets)
 }