Add build.MultiArch.BuildPackageLists

In the terraform module, we call BuildPackageList for each arch:
https://github.com/chainguard-dev/terraform-provider-apko/blob/812478b999411c183e87fefb9a9ece9fe7e8f2c1/internal/provider/config_data_source.go#L239

And then use that package list to actually build the image, so we
separate the solving from the building.

This bypasses chainguard-dev#1180 which
does this multi-arch constraining through a different entrypoint.

This adds another method to the multi-arch stuff that we can opt into
for just the solve part.

Signed-off-by: Jon Johnson <[email protected]>

internal/cli/show-packages.go

@@ -17,17 +17,13 @@ package cli
 import (
 	"context"
 	"fmt"
-	"log/slog"
 	"os"
-	"path/filepath"
 	"text/template"
 
 	"github.com/spf13/cobra"
-	"golang.org/x/exp/slices"
 
 	"github.com/chainguard-dev/clog"
 
-	apkfs "chainguard.dev/apko/pkg/apk/fs"
 	"chainguard.dev/apko/pkg/build"
 	"chainguard.dev/apko/pkg/build/types"
 )
@@ -166,25 +162,21 @@ func ShowPackagesCmd(ctx context.Context, format string, archs []types.Architect
 		return fmt.Errorf("failed to parse format: %w", err)
 	}
 
-	for _, arch := range archs {
-		arch := arch
-		log := clog.New(slog.Default().Handler()).With("arch", arch.ToAPK())
-		ctx = clog.WithLogger(ctx, log)
-
-		// working directory for this architecture
-		wd := filepath.Join(wd, arch.ToAPK())
-		bopts := slices.Clone(opts)
-		bopts = append(bopts, build.WithArch(arch))
-		fs := apkfs.DirFS(wd, apkfs.WithCreateDir())
-		bc, err := build.New(ctx, fs, bopts...)
-		if err != nil {
-			return err
-		}
-		log.Infof("using working directory %s", wd)
+	opts = append(opts, build.WithImageConfiguration(*ic))
+
+	mc, err := build.NewMultiArch(ctx, archs, opts...)
+	if err != nil {
+		return err
+	}
+
+	lists, err := mc.BuildPackageLists(ctx)
+	if err != nil {
+		return fmt.Errorf("failed to get package list for image: %w", err)
+	}
 
-		pkgs, _, err := bc.BuildPackageList(ctx)
-		if err != nil {
-			return fmt.Errorf("failed to get package list for image: %w", err)
+	for arch, pkgs := range lists {
+		if len(archs) != 1 {
+			log.Infof("packages for %s", arch)
 		}
 		var p pkgInfo
 		for _, pkg := range pkgs {

pkg/build/multi.go

@@ -76,14 +76,54 @@ func (m *MultiArch) BuildLayers(ctx context.Context) (map[types.Architecture]v1.
 
 		g.Go(func() error {
 			_, layer, err := bc.BuildLayer(ctx)
+
+			mu.Lock()
+			defer mu.Unlock()
+
 			if err != nil {
 				errs = append(errs, fmt.Errorf("for arch %q: %w", arch, err))
 				return nil
 			}
 
+			layers[arch] = layer
+
+			return nil
+		})
+	}
+
+	if err := g.Wait(); err != nil {
+		return nil, err
+	}
+
+	if err := errors.Join(errs...); err != nil {
+		return nil, fmt.Errorf("building layers: %w", err)
+	}
+
+	return layers, nil
+}
+
+func (m *MultiArch) BuildPackageLists(ctx context.Context) (map[types.Architecture][]*apk.RepositoryPackage, error) {
+	var (
+		g  errgroup.Group
+		mu sync.Mutex
+	)
+	toInstalls := map[types.Architecture][]*apk.RepositoryPackage{}
+	errs := []error{}
+	for arch, bc := range m.Contexts {
+		arch, bc := arch, bc
+
+		g.Go(func() error {
+			toInstall, _, err := bc.apk.ResolveWorld(ctx)
+
 			mu.Lock()
 			defer mu.Unlock()
-			layers[arch] = layer
+
+			if err != nil {
+				errs = append(errs, fmt.Errorf("for arch %q: %w", arch, err))
+				return nil
+			}
+
+			toInstalls[arch] = toInstall
 
 			return nil
 		})
@@ -93,5 +133,9 @@ func (m *MultiArch) BuildLayers(ctx context.Context) (map[types.Architecture]v1.
 		return nil, err
 	}
 
-	return layers, errors.Join(errs...)
+	if err := errors.Join(errs...); err != nil {
+		return nil, fmt.Errorf("resolving apk packages: %w", err)
+	}
+
+	return toInstalls, errors.Join(errs...)
 }