Consolidate all App code into Command

cli.go

@@ -3,13 +3,13 @@
 // cli application can be written as follows:
 //
 //	func main() {
-//		(&cli.App{}).Run(os.Args)
+//		(&cli.Command{}).Run(context.Background(), os.Args)
 //	}
 //
 // Of course this application does not do much, so let's make this an actual application:
 //
 //	func main() {
-//		app := &cli.App{
+//		cmd := &cli.Command{
 //	  		Name: "greet",
 //	  		Usage: "say a greeting",
 //	  		Action: func(c *cli.Context) error {
@@ -18,6 +18,45 @@
 //	  		},
 //		}
 //
-//		app.Run(os.Args)
+//		cmd.Run(context.Background(), os.Args)
 //	}
 package cli
+
+import (
+	"fmt"
+	"os"
+	"runtime"
+	"strings"
+)
+
+var (
+	isTracingOn = os.Getenv("URFAVE_CLI_TRACING") == "on"
+)
+
+func tracef(format string, a ...any) {
+	if !isTracingOn {
+		return
+	}
+
+	if !strings.HasSuffix(format, "\n") {
+		format = format + "\n"
+	}
+
+	pc, file, line, _ := runtime.Caller(1)
+	cf := runtime.FuncForPC(pc)
+
+	fmt.Fprintf(
+		os.Stderr,
+		strings.Join([]string{
+			"## URFAVE CLI TRACE ",
+			file,
+			":",
+			fmt.Sprintf("%v", line),
+			" ",
+			fmt.Sprintf("(%s)", cf.Name()),
+			" ",
+			format,
+		}, ""),
+		a...,
+	)
+}

cli_test.go

@@ -0,0 +1,28 @@
+package cli
+
+import (
+	"bytes"
+	"context"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func expectFileContent(t *testing.T, file, got string) {
+	data, err := os.ReadFile(file)
+	// Ignore windows line endings
+	data = bytes.ReplaceAll(data, []byte("\r\n"), []byte("\n"))
+
+	r := require.New(t)
+	r.NoError(err)
+	r.Equal(got, string(data))
+}
+
+func buildTestContext(t *testing.T) context.Context {
+	ctx, cancel := context.WithTimeout(context.Background(), 100*time.Millisecond)
+	t.Cleanup(cancel)
+
+	return ctx
+}