feat(fly): add `background` option to `execute` command

Signed-off-by: Jonathan Giroux <giroux.jo@gmail.com>

fly/commands/execute.go

@@ -24,6 +24,7 @@ import (
 )
 
 type ExecuteCommand struct {
+	Background     bool                               `short:"b" long:"background"                            description:"Create the build and exit, i.e. neither watch logs nor retrieve outputs."`
 	TaskConfig     atc.PathFlag                       `short:"c" long:"config" required:"true"                description:"The task config to execute"`
 	Privileged     bool                               `short:"p" long:"privileged"                            description:"Run the task with full privileges"`
 	IncludeIgnored bool                               `          long:"include-ignored"                       description:"Including .gitignored paths. Disregards .gitignore entries and uploads everything"`
@@ -85,6 +86,10 @@ func (command *ExecuteCommand) Execute(args []string) error {
 		return err
 	}
 
+	if len(outputs) > 0 && command.Background {
+		return fmt.Errorf("background execution cannot withstand outputs")
+	}
+
 	plan, err := executehelpers.CreateBuildPlan(
 		planFactory,
 		target,
@@ -129,6 +134,11 @@ func (command *ExecuteCommand) Execute(args []string) error {
 
 	fmt.Printf("executing build %d at %s\n", build.ID, clientURL.ResolveReference(buildURL))
 
+	if command.Background {
+		os.Exit(0)
+		return nil
+	}
+
 	terminate := make(chan os.Signal, 1)
 
 	go abortOnSignal(client, terminate, build)

testflight/flying_test.go

@@ -80,6 +80,11 @@ run:
 		Expect(execS).To(gbytes.Say("ARGS are SOME ARGS"))
 	})
 
+	It("works in background", func() {
+		execS := flyIn(tmp, "execute", "-c", "task.yml", "-i", "fixture=./fixture", "-i", "input-1=./input-1", "-i", "input-2=./input-2", "--background", "--", "SOME", "ARGS",)
+		Eventually(execS).Should(gbytes.Say("executing build"))
+	})
+
 	Describe("hijacking", func() {
 		It("executes an interactive command in a running task's container", func() {
 			err := os.WriteFile(