Add failing test for #1373

altsrc/yaml_file_loader_test.go

@@ -0,0 +1,87 @@
+package altsrc_test
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"time"
+
+	"github.com/urfave/cli/v2"
+	"github.com/urfave/cli/v2/altsrc"
+)
+
+func ExampleApp_Run_yamlFileLoaderDuration() {
+	execServe := func(c *cli.Context) error {
+		keepaliveInterval := c.Duration("keepalive-interval")
+		fmt.Printf("keepalive %s\n", keepaliveInterval)
+		return nil
+	}
+
+	fileExists := func(filename string) bool {
+		stat, _ := os.Stat(filename)
+		return stat != nil
+	}
+
+	// initConfigFileInputSource is like altsrc.InitInputSourceWithContext and altsrc.NewYamlSourceFromFlagFunc, but checks
+	// if the config flag is exists and only loads it if it does. If the flag is set and the file exists, it fails.
+	initConfigFileInputSource := func(configFlag string, flags []cli.Flag) cli.BeforeFunc {
+		return func(context *cli.Context) error {
+			configFile := context.String(configFlag)
+			if context.IsSet(configFlag) && !fileExists(configFile) {
+				return fmt.Errorf("config file %s does not exist", configFile)
+			} else if !context.IsSet(configFlag) && !fileExists(configFile) {
+				return nil
+			}
+			inputSource, err := altsrc.NewYamlSourceFromFile(configFile)
+			if err != nil {
+				return err
+			}
+			return altsrc.ApplyInputSourceValues(context, inputSource, flags)
+		}
+	}
+
+	flagsServe := []cli.Flag{
+		&cli.StringFlag{
+			Name:        "config",
+			Aliases:     []string{"c"},
+			EnvVars:     []string{"CONFIG_FILE"},
+			Value:       "../testdata/empty.yml",
+			DefaultText: "../testdata/empty.yml",
+			Usage:       "config file",
+		},
+		altsrc.NewDurationFlag(
+			&cli.DurationFlag{
+				Name:    "keepalive-interval",
+				Aliases: []string{"k"},
+				EnvVars: []string{"KEEPALIVE_INTERVAL"},
+				Value:   45 * time.Second,
+				Usage:   "interval of keepalive messages",
+			},
+		),
+	}
+
+	cmdServe := &cli.Command{
+		Name:      "serve",
+		Usage:     "Run the server",
+		UsageText: "serve [OPTIONS..]",
+		Action:    execServe,
+		Flags:     flagsServe,
+		Before:    initConfigFileInputSource("config", flagsServe),
+	}
+
+	c := &cli.App{
+		Name:                   "cmd",
+		HideVersion:            true,
+		UseShortOptionHandling: true,
+		Commands: []*cli.Command{
+			cmdServe,
+		},
+	}
+
+	if err := c.Run([]string{"cmd", "serve", "--config", "../testdata/empty.yml"}); err != nil {
+		log.Fatal(err)
+	}
+
+	// Output:
+	// keepalive 45s
+}

testdata/empty.yml

@@ -0,0 +1 @@
+# empty file