build: propagate SOURCE_DATE_EPOCH from the client env

Port docker/buildx PR 1482

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

cmd/nerdctl/builder_build_test.go

@@ -420,3 +420,32 @@ CMD ["echo", "nerdctl-build-notag-string"]
 	base.Cmd("images").AssertOutContains("<none>")
 	base.Cmd("image", "prune", "--force", "--all").AssertOK()
 }
+
+// TestBuildSourceDateEpoch tests that $SOURCE_DATE_EPOCH is propagated from the client env
+// https://github.com/docker/buildx/pull/1482
+func TestBuildSourceDateEpoch(t *testing.T) {
+	testutil.RequiresBuild(t)
+	testutil.DockerIncompatible(t) // Needs buildx v0.10 (https://github.com/docker/buildx/pull/1489)
+	base := testutil.NewBase(t)
+	imageName := testutil.Identifier(t)
+	defer base.Cmd("rmi", imageName).Run()
+
+	dockerfile := fmt.Sprintf(`FROM %s
+ARG SOURCE_DATE_EPOCH
+RUN echo $SOURCE_DATE_EPOCH >/source-date-epoch
+CMD ["cat", "/source-date-epoch"]
+	`, testutil.CommonImage)
+
+	buildCtx, err := createBuildContext(dockerfile)
+	assert.NilError(t, err)
+	defer os.RemoveAll(buildCtx)
+
+	const sourceDateEpochEnvStr = "1111111111"
+	t.Setenv("SOURCE_DATE_EPOCH", sourceDateEpochEnvStr)
+	base.Cmd("build", "-t", imageName, buildCtx).AssertOK()
+	base.Cmd("run", "--rm", imageName).AssertOutExactly(sourceDateEpochEnvStr + "\n")
+
+	const sourceDateEpochArgStr = "2222222222"
+	base.Cmd("build", "-t", imageName, "--build-arg", "SOURCE_DATE_EPOCH="+sourceDateEpochArgStr, buildCtx).AssertOK()
+	base.Cmd("run", "--rm", imageName).AssertOutExactly(sourceDateEpochArgStr + "\n")
+}

pkg/cmd/builder/build.go

@@ -282,8 +282,10 @@ func generateBuildctlArgs(ctx context.Context, options types.BuilderBuildOptions
 		buildctlArgs = append(buildctlArgs, "--opt=platform="+strings.Join(options.Platform, ","))
 	}
 
+	seenBuildArgs := make(map[string]struct{})
 	for _, ba := range strutil.DedupeStrSlice(options.BuildArgs) {
 		arr := strings.Split(ba, "=")
+		seenBuildArgs[arr[0]] = struct{}{}
 		if len(arr) == 1 && len(arr[0]) > 0 {
 			// Avoid masking default build arg value from Dockerfile if environment variable is not set
 			// https://github.com/moby/moby/issues/24101
@@ -314,6 +316,14 @@ func generateBuildctlArgs(ctx context.Context, options types.BuilderBuildOptions
 		}
 	}
 
+	// Propagate SOURCE_DATE_EPOCH from the client env
+	// https://github.com/docker/buildx/pull/1482
+	if v := os.Getenv("SOURCE_DATE_EPOCH"); v != "" {
+		if _, ok := seenBuildArgs["SOURCE_DATE_EPOCH"]; !ok {
+			buildctlArgs = append(buildctlArgs, "--opt=build-arg:SOURCE_DATE_EPOCH="+v)
+		}
+	}
+
 	for _, l := range strutil.DedupeStrSlice(options.Label) {
 		buildctlArgs = append(buildctlArgs, "--opt=label:"+l)
 	}