image build: pass built-in args to dockerfile-json

Signed-off-by: Adam Cmiel <acmiel@redhat.com>

Author: chmeliik

go.mod

@@ -5,6 +5,7 @@ go 1.23.3
 toolchain go1.24.6
 
 require (
+	github.com/containerd/platforms v1.0.0-rc.1
 	github.com/containers/image/v5 v5.36.2
 	github.com/keilerkonzept/dockerfile-json v1.2.2
 	github.com/onsi/gomega v1.38.0
@@ -16,6 +17,7 @@ require (
 
 require (
 	github.com/agext/levenshtein v1.2.3 // indirect
+	github.com/containerd/log v0.1.0 // indirect
 	github.com/containerd/typeurl/v2 v2.2.3 // indirect
 	github.com/containers/storage v1.59.1 // indirect
 	github.com/docker/go-units v0.5.0 // indirect

go.sum

@@ -2,6 +2,10 @@ github.com/Masterminds/semver/v3 v3.3.1 h1:QtNSWtVZ3nBfk8mAOu/B6v7FMJ+NHTIgUPi7r
 github.com/Masterminds/semver/v3 v3.3.1/go.mod h1:4V+yj/TJE1HU9XfppCwVMZq3I84lprf4nC11bSS5beM=
 github.com/agext/levenshtein v1.2.3 h1:YB2fHEn0UJagG8T1rrWknE3ZQzWM06O8AMAatNn7lmo=
 github.com/agext/levenshtein v1.2.3/go.mod h1:JEDfjyjHDjOF/1e4FlBE/PkbqA9OfWu2ki2W0IB5558=
+github.com/containerd/log v0.1.0 h1:TCJt7ioM2cr/tfR8GPbGf9/VRAX8D2B4PjzCpfX540I=
+github.com/containerd/log v0.1.0/go.mod h1:VRRf09a7mHDIRezVKTRCrOq78v577GXq3bSa3EhrzVo=
+github.com/containerd/platforms v1.0.0-rc.1 h1:83KIq4yy1erSRgOVHNk1HYdPvzdJ5CnsWaRoJX4C41E=
+github.com/containerd/platforms v1.0.0-rc.1/go.mod h1:J71L7B+aiM5SdIEqmd9wp6THLVRzJGXfNuWCZCllLA4=
 github.com/containerd/typeurl/v2 v2.2.3 h1:yNA/94zxWdvYACdYO8zofhrTVuQY73fFU1y++dYSw40=
 github.com/containerd/typeurl/v2 v2.2.3/go.mod h1:95ljDnPfD3bAbDJRugOiShd/DlAAsxGtUBhJxIn7SCk=
 github.com/containers/image/v5 v5.36.2 h1:GcxYQyAHRF/pLqR4p4RpvKllnNL8mOBn0eZnqJbfTwk=

integration_tests/build_test.go

@@ -571,6 +571,80 @@ LABEL test.label="build-args-test"
 		Expect(containerfileLabels).To(ContainElements(expectedLabels))
 	})
 
+	t.Run("PlatformBuildArgs", func(t *testing.T) {
+		contextDir := setupTestContext(t)
+
+		writeContainerfile(contextDir, `
+FROM scratch
+
+ARG TARGETPLATFORM
+ARG TARGETOS
+ARG TARGETARCH
+ARG TARGETVARIANT
+ARG BUILDPLATFORM
+ARG BUILDOS
+ARG BUILDARCH
+ARG BUILDVARIANT
+
+LABEL TARGETPLATFORM=$TARGETPLATFORM
+LABEL TARGETOS=$TARGETOS
+LABEL TARGETARCH=$TARGETARCH
+LABEL TARGETVARIANT=$TARGETVARIANT
+LABEL BUILDPLATFORM=$BUILDPLATFORM
+LABEL BUILDOS=$BUILDOS
+LABEL BUILDARCH=$BUILDARCH
+LABEL BUILDVARIANT=$BUILDVARIANT
+
+LABEL test.label="platform-build-args-test"
+`)
+
+		outputRef := "localhost/test-image-platform-build-args:" + GenerateUniqueTag(t)
+		containerfileJsonPath := "/workspace/parsed-containerfile.json"
+
+		buildParams := BuildParams{
+			Context:                 contextDir,
+			OutputRef:               outputRef,
+			Push:                    false,
+			ContainerfileJsonOutput: containerfileJsonPath,
+		}
+
+		container := setupBuildContainerWithCleanup(t, buildParams, nil)
+
+		err := runBuild(container, buildParams)
+		Expect(err).ToNot(HaveOccurred())
+
+		// Verify platform values match between the parsed Containerfile and the actual image
+		imageLabels := getImageLabels(container, outputRef)
+		containerfileLabels := getContainerfileLabels(container, containerfileJsonPath)
+
+		labelsToCheck := []string{
+			"TARGETPLATFORM",
+			"TARGETOS",
+			"TARGETARCH",
+			"TARGETVARIANT",
+			"BUILDPLATFORM",
+			"BUILDOS",
+			"BUILDARCH",
+			"BUILDVARIANT",
+		}
+
+		for _, label := range labelsToCheck {
+			imageLabel := imageLabels[label]
+			containerfileLabel := containerfileLabels[label]
+
+			// the *VARIANT values will be empty on platforms other than ARM
+			expectEmpty := strings.HasSuffix(label, "VARIANT") && runtime.GOARCH != "arm"
+			if !expectEmpty {
+				Expect(imageLabel).ToNot(BeEmpty(), fmt.Sprintf("label %s is empty on the built image", label))
+				Expect(containerfileLabel).ToNot(BeEmpty(), fmt.Sprintf("label %s is empty in the containerfile JSON", label))
+			}
+
+			Expect(imageLabel).To(Equal(containerfileLabel),
+				fmt.Sprintf("image label: %s=%s; containerfile label: %s=%s", label, imageLabel, label, containerfileLabel),
+			)
+		}
+	})
+
 	t.Run("ContainerfileJsonOutput", func(t *testing.T) {
 		contextDir := setupTestContext(t)
 

pkg/commands/build.go

@@ -13,6 +13,7 @@ import (
 	"github.com/konflux-ci/konflux-build-cli/pkg/common"
 	"github.com/spf13/cobra"
 
+	"github.com/containerd/platforms"
 	"github.com/keilerkonzept/dockerfile-json/pkg/buildargs"
 	"github.com/keilerkonzept/dockerfile-json/pkg/dockerfile"
 	l "github.com/konflux-ci/konflux-build-cli/pkg/logger"
@@ -426,9 +427,21 @@ func (c *Build) parseContainerfile() (*dockerfile.Dockerfile, error) {
 }
 
 func (c *Build) createBuildArgExpander() (dockerfile.SingleWordExpander, error) {
-	args := make(map[string]string)
-
-	// Load from --build-args-file
+	// Define built-in ARG variables
+	// See https://docs.docker.com/build/building/variables/#multi-platform-build-arguments
+	platform := platforms.DefaultSpec()
+	args := map[string]string{
+		"TARGETPLATFORM": platforms.Format(platform),
+		"TARGETOS":       platform.OS,
+		"TARGETARCH":     platform.Architecture,
+		"TARGETVARIANT":  platform.Variant,
+		"BUILDPLATFORM":  platforms.Format(platform),
+		"BUILDOS":        platform.OS,
+		"BUILDARCH":      platform.Architecture,
+		"BUILDVARIANT":   platform.Variant,
+	}
+
+	// Load from --build-args-file, can override built-in args
 	if c.Params.BuildArgsFile != "" {
 		fileArgs, err := buildargs.ParseBuildArgFile(c.Params.BuildArgsFile)
 		if err != nil {
@@ -437,7 +450,7 @@ func (c *Build) createBuildArgExpander() (dockerfile.SingleWordExpander, error)
 		maps.Copy(args, fileArgs)
 	}
 
-	// CLI --build-args take precedence
+	// CLI --build-args take precedence over everything else
 	for _, arg := range c.Params.BuildArgs {
 		key, value, hasValue := strings.Cut(arg, "=")
 		if hasValue {

pkg/commands/build_test.go

@@ -673,6 +673,75 @@ func Test_Build_createBuildArgExpander(t *testing.T) {
 		g.Expect(value).To(Equal("from-file"))
 	})
 
+	t.Run("should provide built-in platform args by default", func(t *testing.T) {
+		c := &Build{
+			Params: &BuildParams{},
+		}
+
+		expander, err := c.createBuildArgExpander()
+		g.Expect(err).ToNot(HaveOccurred())
+
+		// Check that all built-in platform args are available
+		platformArgs := []string{
+			"TARGETPLATFORM", "TARGETOS", "TARGETARCH", "TARGETVARIANT",
+			"BUILDPLATFORM", "BUILDOS", "BUILDARCH", "BUILDVARIANT",
+		}
+
+		for _, arg := range platformArgs {
+			value, err := expander(arg)
+			// TARGETVARIANT and BUILDVARIANT can be empty on non-ARM platforms
+			if arg == "TARGETVARIANT" || arg == "BUILDVARIANT" {
+				g.Expect(err).ToNot(HaveOccurred())
+			} else {
+				g.Expect(err).ToNot(HaveOccurred())
+				g.Expect(value).ToNot(BeEmpty(), "arg %s should not be empty", arg)
+			}
+		}
+	})
+
+	t.Run("should allow file args to override built-in platform args", func(t *testing.T) {
+		tempDir := t.TempDir()
+		testutil.WriteFileTree(t, tempDir, map[string]string{
+			"build-args": "TARGETOS=custom-os\nTARGETARCH=custom-arch\n",
+		})
+
+		c := &Build{
+			Params: &BuildParams{
+				BuildArgsFile: filepath.Join(tempDir, "build-args"),
+			},
+		}
+
+		expander, err := c.createBuildArgExpander()
+		g.Expect(err).ToNot(HaveOccurred())
+
+		value, err := expander("TARGETOS")
+		g.Expect(err).ToNot(HaveOccurred())
+		g.Expect(value).To(Equal("custom-os"))
+
+		value, err = expander("TARGETARCH")
+		g.Expect(err).ToNot(HaveOccurred())
+		g.Expect(value).To(Equal("custom-arch"))
+	})
+
+	t.Run("should allow CLI args to override built-in platform args", func(t *testing.T) {
+		c := &Build{
+			Params: &BuildParams{
+				BuildArgs: []string{"TARGETOS=custom-os", "TARGETARCH=custom-arch"},
+			},
+		}
+
+		expander, err := c.createBuildArgExpander()
+		g.Expect(err).ToNot(HaveOccurred())
+
+		value, err := expander("TARGETOS")
+		g.Expect(err).ToNot(HaveOccurred())
+		g.Expect(value).To(Equal("custom-os"))
+
+		value, err = expander("TARGETARCH")
+		g.Expect(err).ToNot(HaveOccurred())
+		g.Expect(value).To(Equal("custom-arch"))
+	})
+
 	t.Run("should return error for undefined build arg", func(t *testing.T) {
 		c := &Build{
 			Params: &BuildParams{},