Create a global variable to hold output file

With a function scoped `os.File`, next time the GC passes
the instance is collected, calling the finalizer and triggering
the invalidation of the FD, that cannot be used anymore.

Signed-off-by: Ulysses Souza <ulysses.souza@docker.com>

internal/commands/build/build.go

@@ -23,6 +23,7 @@ import (
 	"github.com/docker/cli/cli"
 	"github.com/docker/cli/cli/command"
 	compose "github.com/docker/cli/cli/compose/types"
+	"github.com/docker/cli/cli/streams"
 	"github.com/docker/cnab-to-oci/remotes"
 	"github.com/docker/distribution/reference"
 	"github.com/moby/buildkit/client"
@@ -49,6 +50,8 @@ type buildOptions struct {
 const buildExample = `- $ docker app build .
 - $ docker app build --file myapp.dockerapp --tag myrepo/myapp:1.0.0 .`
 
+var outputFile *os.File
+
 func Cmd(dockerCli command.Cli) *cobra.Command {
 	var opts buildOptions
 	cmd := &cobra.Command{
@@ -136,6 +139,22 @@ func runBuild(dockerCli command.Cli, contextPath string, opt buildOptions) error
 	return err
 }
 
+func getOutputFile(realOut *streams.Out, quiet bool) (*os.File, error) {
+	if outputFile != nil {
+		return outputFile, nil
+	}
+	if quiet {
+		var err error
+		outputFile, err = os.Create(os.DevNull)
+		if err != nil {
+			return nil, err
+		}
+		return outputFile, nil
+	}
+	outputFile = os.NewFile(realOut.FD(), os.Stdout.Name())
+	return outputFile, nil
+}
+
 func buildImageUsingBuildx(app *types.App, contextPath string, opt buildOptions, dockerCli command.Cli) (*bundle.Bundle, error) {
 	buildopts, pulledServices, err := parseCompose(app, contextPath, opt)
 	if err != nil {
@@ -160,13 +179,9 @@ func buildImageUsingBuildx(app *types.App, contextPath string, opt buildOptions,
 		},
 	}
 
-	var out *os.File
-	if opt.quiet {
-		if out, err = os.Create(os.DevNull); err != nil {
-			return nil, err
-		}
-	} else {
-		out = os.NewFile(dockerCli.Out().FD(), "/dev/stdout")
+	out, err := getOutputFile(dockerCli.Out(), opt.quiet)
+	if err != nil {
+		return nil, err
 	}
 
 	pw := progress.NewPrinter(ctx, out, opt.progress)