add support for default global args (#44)

* add support for default global args

* add `BuildPlatform` property to `BOpts`

* apply feedbacks from the review

* add unit tests for frontend `globalArgs` and `resolveStates`

* support a list of build platforms

Author: stevapple

pkg/build/buildopts.go

@@ -23,12 +23,13 @@ import (
 	"path/filepath"
 	"strings"
 
-	"github.com/containerd/containerd/platforms"
+	"github.com/containerd/platforms"
 	"github.com/moby/buildkit/frontend/dockerfile/instructions"
 	"github.com/moby/buildkit/frontend/dockerfile/parser"
 	"github.com/moby/buildkit/util/progress/progresswriter"
 	ocispecs "github.com/opencontainers/image-spec/specs-go/v1"
 
+	"github.com/apple/container-builder-shim/pkg/build/utils"
 	"github.com/apple/container-builder-shim/pkg/content"
 	"github.com/apple/container-builder-shim/pkg/fssync"
 	"github.com/apple/container-builder-shim/pkg/resolver"
@@ -63,6 +64,7 @@ type BOpts struct {
 	Dockerfile     []byte
 	Tag            string
 	ContextDir     string
+	BuildPlatforms []ocispecs.Platform
 	Platforms      []ocispecs.Platform
 	NoCache        bool
 	Target         string
@@ -131,6 +133,11 @@ func NewBuildOpts(ctx context.Context, basePath string, contextMap map[string][]
 		ctxDir = c
 	}
 
+	bps := utils.BuildPlatforms()
+	if len(bps) == 0 {
+		bps = append(bps, platforms.DefaultSpec())
+	}
+
 	pls, err := func() ([]ocispecs.Platform, error) {
 		pls := []ocispecs.Platform{}
 		values, ok := contextMap[KeyPlatforms]
@@ -231,6 +238,7 @@ func NewBuildOpts(ctx context.Context, basePath string, contextMap map[string][]
 		BuildID:        buildID,
 		Dockerfile:     dockerfileBytes,
 		Tag:            tag,
+		BuildPlatforms: bps,
 		Platforms:      pls,
 		ContextDir:     ctxDir,
 		ContentStore:   contentProxy,

pkg/build/frontend.go

@@ -135,7 +135,8 @@ func resolveStates(ctx context.Context, bopts *BOpts, platform ocispecs.Platform
 			defer wg.Done()
 
 			shlex := shell.NewLex(dockerfile.EscapeToken)
-			resolvedBaseStageName, err := shlex.ProcessWordWithMatches(stage.BaseName, utils.NewMapGetter(bopts.BuildArgs))
+			resolvedGlobalArgs := globalArgs(bopts.BuildPlatforms[0], platform, bopts.BuildArgs, bopts.Target)
+			resolvedBaseStageName, err := shlex.ProcessWordWithMatches(stage.BaseName, resolvedGlobalArgs)
 			if err != nil {
 				errCh <- fmt.Errorf("invalid arg for stage[%s]: %v", stage.BaseName, err)
 				return
@@ -145,6 +146,22 @@ func resolveStates(ctx context.Context, bopts *BOpts, platform ocispecs.Platform
 				return
 			}
 
+			// if platform is specified for the stage, parse and use as the target platform
+			stagePlatform := platform
+			if stage.Platform != "" {
+				resolvedStagePlatformStr, err := shlex.ProcessWordWithMatches(stage.Platform, resolvedGlobalArgs)
+				if err != nil {
+					errCh <- fmt.Errorf("invalid platform for stage[%s]: %v", stage.BaseName, err)
+					return
+				}
+				resolvedStagePlatform, err := platforms.Parse(resolvedStagePlatformStr.Result)
+				if err != nil {
+					errCh <- fmt.Errorf("invalid platform for stage[%s]: %v", stage.BaseName, err)
+					return
+				}
+				stagePlatform = resolvedStagePlatform
+			}
+
 			// if there's another stage with this name before the current stage, that will be used as the source
 			namedIndex, hasNamedStage := instructions.HasStage(stages, resolvedBaseStageName.Result)
 			if hasNamedStage && namedIndex < i {
@@ -164,7 +181,7 @@ func resolveStates(ctx context.Context, bopts *BOpts, platform ocispecs.Platform
 			clog("[resolver] fetching image...%s", ref.String())
 
 			resolverOpts := sourceresolver.Opt{
-				Platform: &platform,
+				Platform: &stagePlatform,
 			}
 			resolverOpts.OCILayoutOpt = &sourceresolver.ResolveOCILayoutOpt{
 				Store: sourceresolver.ResolveImageConfigOptStore{
@@ -196,7 +213,7 @@ func resolveStates(ctx context.Context, bopts *BOpts, platform ocispecs.Platform
 				fqdn = fqdn + "@" + digest.String()
 			}
 			logrus.WithField("ref", fqdn).Infof("creating llb")
-			st := llb.OCILayout(fqdn, llb.OCIStore("", "container"), llb.Platform(platform))
+			st := llb.OCILayout(fqdn, llb.OCIStore("", "container"), llb.Platform(stagePlatform))
 
 			named, err := dref.ParseNormalizedNamed(ref.String())
 			if err != nil {
@@ -206,7 +223,7 @@ func resolveStates(ctx context.Context, bopts *BOpts, platform ocispecs.Platform
 			name := strings.TrimSuffix(dref.FamiliarString(named), ":latest")
 
 			// pname constructs a platform-qualified image reference in the format buildkit requires for digest resolution
-			pname := name + "::" + platforms.FormatAll(platforms.Normalize(platform))
+			pname := name + "::" + platforms.FormatAll(platforms.Normalize(stagePlatform))
 			imgMetaMap := map[string][]byte{
 				exptypes.ExporterImageConfigKey: img,
 			}
@@ -221,7 +238,7 @@ func resolveStates(ctx context.Context, bopts *BOpts, platform ocispecs.Platform
 			defer stateLock.Unlock()
 
 			states[pname] = stateMeta{
-				state:   st.Platform(platform),
+				state:   st.Platform(stagePlatform),
 				imgMeta: imgMeta,
 			}
 		}(stage)
@@ -317,7 +334,7 @@ func solvePlatform(ctx context.Context, bopts *BOpts, pl ocispecs.Platform, c ga
 		Client:         cl,
 	}
 
-	convertOpt.BuildPlatforms = utils.BuildPlatforms()
+	convertOpt.BuildPlatforms = bopts.BuildPlatforms
 	convertOpt.TargetPlatforms = bopts.Platforms
 	convertOpt.BuildArgs = bopts.BuildArgs
 	convertOpt.Labels = bopts.Labels
@@ -377,3 +394,26 @@ func solvePlatform(ctx context.Context, bopts *BOpts, pl ocispecs.Platform, c ga
 	}
 	return ref, cfgJSON, nil
 }
+
+func globalArgs(buildPlatform, targetPlatform ocispecs.Platform, buildArgs map[string]string, target string) utils.MapGetter {
+	if target == "" {
+		target = "default"
+	}
+	args := map[string]string{
+		"BUILDPLATFORM":   platforms.Format(buildPlatform),
+		"BUILDOS":         buildPlatform.OS,
+		"BUILDOSVERSION":  buildPlatform.OSVersion,
+		"BUILDARCH":       buildPlatform.Architecture,
+		"BUILDVARIANT":    buildPlatform.Variant,
+		"TARGETPLATFORM":  platforms.FormatAll(targetPlatform),
+		"TARGETOS":        targetPlatform.OS,
+		"TARGETOSVERSION": targetPlatform.OSVersion,
+		"TARGETARCH":      targetPlatform.Architecture,
+		"TARGETVARIANT":   targetPlatform.Variant,
+		"TARGETSTAGE":     target,
+	}
+	for k, v := range buildArgs {
+		args[k] = v
+	}
+	return utils.NewMapGetter(args)
+}