use go-arg fork

pkg/common/config.go

@@ -8,9 +8,9 @@ import (
 )
 
 type Config struct {
-	Logging ConfigLogging `arg:"-"`
-	Stream  ConfigStream  `arg:"-"`
-	Http    ConfigHTTP    `arg:"-"`
+	Logging ConfigLogging `arg:"group:Logging"`
+	Stream  ConfigStream  `arg:"group:Stream"`
+	Http    ConfigHTTP    `arg:"group:Http"`
 }
 
 type ConfigLogging struct {
@@ -26,9 +26,9 @@ type ConfigHTTP struct {
 }
 
 type ConfigStream struct {
-	VideoOut ConfigVideoOutputStream `arg:"-"`
-	AudioOut ConfigAudioOutputStream `arg:"-"`
-	AudioIn  ConfigAudioInputStream  `arg:"-"`
+	VideoOut ConfigVideoOutputStream `arg:"group:VideoOut"`
+	AudioOut ConfigAudioOutputStream `arg:"group:AudioOut"`
+	AudioIn  ConfigAudioInputStream  `arg:"group:AudioIn"`
 }
 
 type ConfigVideoOutputStream struct {
@@ -60,10 +60,5 @@ func (c *ConfigHTTP) Address() string {
 }
 
 func (c *Config) MustParse() {
-	arg.MustParse(&c.Logging)
-	arg.MustParse(&c.Stream.VideoOut)
-	arg.MustParse(&c.Stream.AudioOut)
-	arg.MustParse(&c.Stream.AudioIn)
-	arg.MustParse(&c.Http)
 	arg.MustParse(c)
 }

vendor/github.com/alexflint/go-arg/.github/workflows/go.yml

@@ -0,0 +1,37 @@
+name: Go
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+
+  build_and_test:
+    name: Build and test
+    runs-on: ubuntu-latest
+
+    strategy:
+      fail-fast: false
+      matrix:
+        go: ['1.17', '1.18', '1.19']
+
+    steps:
+    - id: go
+      name: Set up Go
+      uses: actions/setup-go@v3
+      with:
+        go-version: ${{ matrix.go }}
+
+    - name: Checkout
+      uses: actions/checkout@v3
+
+    - name: Build
+      run: go build -v .
+    
+    - name: Test
+      run: go test -v -coverprofile=profile.cov .
+
+    - name: Send coverage
+      run: bash <(curl -s https://codecov.io/bash) -f profile.cov

vendor/github.com/alexflint/go-arg/README.md

@@ -134,10 +134,10 @@ arg.MustParse(&args)
 
 ```shell
 $ ./example -h
-Usage: [--verbose] [--dataset DATASET] [--optimize OPTIMIZE] [--help] INPUT [OUTPUT [OUTPUT ...]] 
+Usage: [--verbose] [--dataset DATASET] [--optimize OPTIMIZE] [--help] INPUT [OUTPUT [OUTPUT ...]]
 
 Positional arguments:
-  INPUT 
+  INPUT
   OUTPUT
 
 Options:
@@ -180,6 +180,24 @@ var args struct {
 arg.MustParse(&args)
 ```
 
+#### Ignoring environment variables and/or default values
+
+The values in an existing structure can be kept in-tact by ignoring environment
+variables and/or default values.
+
+```go
+var args struct {
+    Test  string `arg:"-t,env:TEST" default:"something"`
+}
+
+p, err := arg.NewParser(arg.Config{
+    IgnoreEnv: true,
+    IgnoreDefault: true,
+}, &args)
+
+err = p.Parse(os.Args)
+```
+
 ### Arguments with multiple values
 ```go
 var args struct {
@@ -444,6 +462,9 @@ Options:
 
 ### Description strings
 
+A descriptive message can be added at the top of the help text by implementing
+a `Description` function that returns a string.
+
 ```go
 type args struct {
 	Foo string
@@ -469,6 +490,35 @@ Options:
   --help, -h             display this help and exit
 ```
 
+Similarly an epilogue can be added at the end of the help text by implementing
+the `Epilogue` function.
+
+```go
+type args struct {
+	Foo string
+}
+
+func (args) Epilogue() string {
+	return "For more information visit github.com/alexflint/go-arg"
+}
+
+func main() {
+	var args args
+	arg.MustParse(&args)
+}
+```
+
+```shell
+$ ./example -h
+Usage: example [--foo FOO]
+
+Options:
+  --foo FOO
+  --help, -h             display this help and exit
+
+For more information visit github.com/alexflint/go-arg
+```
+
 ### Subcommands
 
 *Introduced in version 1.1.0*
@@ -533,6 +583,71 @@ if p.Subcommand() == nil {
 }
 ```
 
+### Option groups
+
+Option groups are a hybrid between subcommands and embedded structs. Option
+groups create logical collections of related arguments with a help description,
+and can be embedded in other groups and subcommands. Option groups can combine
+configuration structs of multiple modules without requiring embedding.
+
+```go
+type Repository struct {
+    URL      string       `arg:"--host" help:"URL of the repository" default:"docker.io"`
+    User     string       `arg:"--user,env:REPO_USERNAME" help:"username to connect as"`
+    Password string       `arg:"--,env:REPO_PASSWORD" help:"password to connect with"`
+}
+type BuildCmd struct {
+        Context  string
+        Tag      string
+}
+type PushCmd struct {
+        Repo     Repository  `arg:"group:Repository" help:"Change the default registry to push to."`
+        Tag      string `help:"Tag"`
+}
+var args struct {
+        Build    *BuildCmd    `arg:"subcommand:build"`
+        Push     *PushCmd     `arg:"subcommand:push"`
+        Quiet    bool         `arg:"-q" help:"Quiet"` // this flag is global to all subcommands
+}
+
+arg.MustParse(&args)
+
+switch {
+case args.Build != nil:
+        fmt.Printf("build %s as %q\n", args.Build.Context, args.Build.Tag)
+case args.Push != nil:
+        fmt.Printf("push %q to %q\n", args.Push.Tag, args.Push.Repo.URL)
+}
+```
+
+The push command help message would look like:
+
+```text
+Usage: example push [--tag TAG] [--host HOST] [--user USER]
+
+Options:
+  --tag TAG              Tag
+
+Repository options:
+
+Change the default registry to push to.
+
+  --host HOST            URL of the repository [default: docker.io]
+  --user USER            username to connect as [env: REPO_USERNAME]
+  (environment only)     password to connect with [env: REPO_PASSWORD]
+
+Global options:
+  --quiet, -q            Quiet
+  --help, -h             display this help and exit
+```
+
+Some additional rules apply when working with option groups:
+* The `group` tag can only be used with fields that are structs or pointers to structs.
+* Specifying default values in nested struct pointers _always_ result in an initialized struct.
+* Option groups may not contain any positionals.
+* Option groups cannot contain sub-commands.
+```
+
 ### API Documentation
 
 https://godoc.org/github.com/alexflint/go-arg

vendor/github.com/alexflint/go-arg/example_test.go

@@ -0,0 +1,545 @@
+package arg
+
+import (
+	"fmt"
+	"net"
+	"net/mail"
+	"net/url"
+	"os"
+	"strings"
+	"time"
+)
+
+func split(s string) []string {
+	return strings.Split(s, " ")
+}
+
+// This example demonstrates basic usage
+func Example() {
+	// These are the args you would pass in on the command line
+	os.Args = split("./example --foo=hello --bar")
+
+	var args struct {
+		Foo string
+		Bar bool
+	}
+	MustParse(&args)
+	fmt.Println(args.Foo, args.Bar)
+	// output: hello true
+}
+
+// This example demonstrates arguments that have default values
+func Example_defaultValues() {
+	// These are the args you would pass in on the command line
+	os.Args = split("./example")
+
+	var args struct {
+		Foo string `default:"abc"`
+	}
+	MustParse(&args)
+	fmt.Println(args.Foo)
+	// output: abc
+}
+
+// This example demonstrates arguments that are required
+func Example_requiredArguments() {
+	// These are the args you would pass in on the command line
+	os.Args = split("./example --foo=abc --bar")
+
+	var args struct {
+		Foo string `arg:"required"`
+		Bar bool
+	}
+	MustParse(&args)
+	fmt.Println(args.Foo, args.Bar)
+	// output: abc true
+}
+
+// This example demonstrates positional arguments
+func Example_positionalArguments() {
+	// These are the args you would pass in on the command line
+	os.Args = split("./example in out1 out2 out3")
+
+	var args struct {
+		Input  string   `arg:"positional"`
+		Output []string `arg:"positional"`
+	}
+	MustParse(&args)
+	fmt.Println("In:", args.Input)
+	fmt.Println("Out:", args.Output)
+	// output:
+	// In: in
+	// Out: [out1 out2 out3]
+}
+
+// This example demonstrates arguments that have multiple values
+func Example_multipleValues() {
+	// The args you would pass in on the command line
+	os.Args = split("./example --database localhost --ids 1 2 3")
+
+	var args struct {
+		Database string
+		IDs      []int64
+	}
+	MustParse(&args)
+	fmt.Printf("Fetching the following IDs from %s: %v", args.Database, args.IDs)
+	// output: Fetching the following IDs from localhost: [1 2 3]
+}
+
+// This example demonstrates arguments with keys and values
+func Example_mappings() {
+	// The args you would pass in on the command line
+	os.Args = split("./example --userids john=123 mary=456")
+
+	var args struct {
+		UserIDs map[string]int
+	}
+	MustParse(&args)
+	fmt.Println(args.UserIDs)
+	// output: map[john:123 mary:456]
+}
+
+type commaSeparated struct {
+	M map[string]string
+}
+
+func (c *commaSeparated) UnmarshalText(b []byte) error {
+	c.M = make(map[string]string)
+	for _, part := range strings.Split(string(b), ",") {
+		pos := strings.Index(part, "=")
+		if pos == -1 {
+			return fmt.Errorf("error parsing %q, expected format key=value", part)
+		}
+		c.M[part[:pos]] = part[pos+1:]
+	}
+	return nil
+}
+
+// This example demonstrates arguments with keys and values separated by commas
+func Example_mappingWithCommas() {
+	// The args you would pass in on the command line
+	os.Args = split("./example --values one=two,three=four")
+
+	var args struct {
+		Values commaSeparated
+	}
+	MustParse(&args)
+	fmt.Println(args.Values.M)
+	// output: map[one:two three:four]
+}
+
+// This eample demonstrates multiple value arguments that can be mixed with
+// other arguments.
+func Example_multipleMixed() {
+	os.Args = split("./example -c cmd1 db1 -f file1 db2 -c cmd2 -f file2 -f file3 db3 -c cmd3")
+	var args struct {
+		Commands  []string `arg:"-c,separate"`
+		Files     []string `arg:"-f,separate"`
+		Databases []string `arg:"positional"`
+	}
+	MustParse(&args)
+	fmt.Println("Commands:", args.Commands)
+	fmt.Println("Files:", args.Files)
+	fmt.Println("Databases:", args.Databases)
+
+	// output:
+	// Commands: [cmd1 cmd2 cmd3]
+	// Files: [file1 file2 file3]
+	// Databases: [db1 db2 db3]
+}
+
+// This example shows the usage string generated by go-arg
+func Example_helpText() {
+	// These are the args you would pass in on the command line
+	os.Args = split("./example --help")
+
+	var args struct {
+		Input    string   `arg:"positional,required"`
+		Output   []string `arg:"positional"`
+		Verbose  bool     `arg:"-v" help:"verbosity level"`
+		Dataset  string   `help:"dataset to use"`
+		Optimize int      `arg:"-O,--optim" help:"optimization level"`
+	}
+
+	// This is only necessary when running inside golang's runnable example harness
+	mustParseExit = func(int) {}
+
+	MustParse(&args)
+
+	// output:
+	// Usage: example [--verbose] [--dataset DATASET] [--optim OPTIM] INPUT [OUTPUT [OUTPUT ...]]
+	//
+	// Positional arguments:
+	//   INPUT
+	//   OUTPUT
+	//
+	// Options:
+	//   --verbose, -v          verbosity level
+	//   --dataset DATASET      dataset to use
+	//   --optim OPTIM, -O OPTIM
+	//                          optimization level
+	//   --help, -h             display this help and exit
+}
+
+// This example shows the usage string generated by go-arg with customized placeholders
+func Example_helpPlaceholder() {
+	// These are the args you would pass in on the command line
+	os.Args = split("./example --help")
+
+	var args struct {
+		Input    string   `arg:"positional,required" placeholder:"SRC"`
+		Output   []string `arg:"positional" placeholder:"DST"`
+		Optimize int      `arg:"-O" help:"optimization level" placeholder:"LEVEL"`
+		MaxJobs  int      `arg:"-j" help:"maximum number of simultaneous jobs" placeholder:"N"`
+	}
+
+	// This is only necessary when running inside golang's runnable example harness
+	mustParseExit = func(int) {}
+
+	MustParse(&args)
+
+	// output:
+
+	// Usage: example [--optimize LEVEL] [--maxjobs N] SRC [DST [DST ...]]
+
+	// Positional arguments:
+	//   SRC
+	//   DST
+
+	// Options:
+	//   --optimize LEVEL, -O LEVEL
+	//                          optimization level
+	//   --maxjobs N, -j N      maximum number of simultaneous jobs
+	//   --help, -h             display this help and exit
+}
+
+// This example shows the usage string generated by go-arg when using subcommands
+func Example_helpTextWithSubcommand() {
+	// These are the args you would pass in on the command line
+	os.Args = split("./example --help")
+
+	type getCmd struct {
+		Item string `arg:"positional" help:"item to fetch"`
+	}
+
+	type listCmd struct {
+		Format string `help:"output format"`
+		Limit  int
+	}
+
+	var args struct {
+		Verbose bool
+		Get     *getCmd  `arg:"subcommand" help:"fetch an item and print it"`
+		List    *listCmd `arg:"subcommand" help:"list available items"`
+	}
+
+	// This is only necessary when running inside golang's runnable example harness
+	mustParseExit = func(int) {}
+
+	MustParse(&args)
+
+	// output:
+	// Usage: example [--verbose] <command> [<args>]
+	//
+	// Options:
+	//   --verbose
+	//   --help, -h             display this help and exit
+	//
+	// Commands:
+	//   get                    fetch an item and print it
+	//   list                   list available items
+}
+
+// This example shows the usage string generated by go-arg when using argument groups
+func Example_helpTextWithGroups() {
+	os.Args = split("./example push --help")
+
+	type Repository struct {
+		URL      string `arg:"--host" help:"URL of the repository" default:"docker.io"`
+		User     string `arg:"--user,env:REPO_USERNAME" help:"username to connect as"`
+		Password string `arg:"--,env:REPO_PASSWORD" help:"password to connect with"`
+	}
+	type BuildCmd struct {
+		Context string
+		Tag     string
+	}
+	type PushCmd struct {
+		Repo Repository `arg:"group:Repository" help:"Change the default registry to push to."`
+		Tag  string     `help:"Tag"`
+	}
+	var args struct {
+		Build *BuildCmd `arg:"subcommand:build"`
+		Push  *PushCmd  `arg:"subcommand:push"`
+		Quiet bool      `arg:"-q" help:"Quiet"` // this flag is global to all subcommands
+	}
+
+	// This is only necessary when running inside golang's runnable example harness
+	mustParseExit = func(int) {}
+
+	MustParse(&args)
+
+	// output:
+	// Usage: example push [--tag TAG] [--host HOST] [--user USER]
+	//
+	// Options:
+	//   --tag TAG              Tag
+	//
+	// Repository options:
+	//
+	// Change the default registry to push to.
+	//
+	//   --host HOST            URL of the repository [default: docker.io]
+	//   --user USER            username to connect as [env: REPO_USERNAME]
+	//   (environment only)     password to connect with [env: REPO_PASSWORD]
+	//
+	// Global options:
+	//   --quiet, -q            Quiet
+	//   --help, -h             display this help and exit
+}
+
+// This example shows the usage string generated by go-arg when using subcommands
+func Example_helpTextWhenUsingSubcommand() {
+	// These are the args you would pass in on the command line
+	os.Args = split("./example get --help")
+
+	type getCmd struct {
+		Item string `arg:"positional,required" help:"item to fetch"`
+	}
+
+	type listCmd struct {
+		Format string `help:"output format"`
+		Limit  int
+	}
+
+	var args struct {
+		Verbose bool
+		Get     *getCmd  `arg:"subcommand" help:"fetch an item and print it"`
+		List    *listCmd `arg:"subcommand" help:"list available items"`
+	}
+
+	// This is only necessary when running inside golang's runnable example harness
+	mustParseExit = func(int) {}
+
+	MustParse(&args)
+
+	// output:
+	// Usage: example get ITEM
+	//
+	// Positional arguments:
+	//   ITEM                   item to fetch
+	//
+	// Global options:
+	//   --verbose
+	//   --help, -h             display this help and exit
+}
+
+// This example shows how to print help for an explicit subcommand
+func Example_writeHelpForSubcommand() {
+	// These are the args you would pass in on the command line
+	os.Args = split("./example get --help")
+
+	type getCmd struct {
+		Item string `arg:"positional" help:"item to fetch"`
+	}
+
+	type listCmd struct {
+		Format string `help:"output format"`
+		Limit  int
+	}
+
+	var args struct {
+		Verbose bool
+		Get     *getCmd  `arg:"subcommand" help:"fetch an item and print it"`
+		List    *listCmd `arg:"subcommand" help:"list available items"`
+	}
+
+	// This is only necessary when running inside golang's runnable example harness
+	exit := func(int) {}
+
+	p, err := NewParser(Config{Exit: exit}, &args)
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+
+	err = p.WriteHelpForSubcommand(os.Stdout, "list")
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+
+	// output:
+	// Usage: example list [--format FORMAT] [--limit LIMIT]
+	//
+	// Options:
+	//   --format FORMAT        output format
+	//   --limit LIMIT
+	//
+	// Global options:
+	//   --verbose
+	//   --help, -h             display this help and exit
+}
+
+// This example shows how to print help for a subcommand that is nested several levels deep
+func Example_writeHelpForSubcommandNested() {
+	// These are the args you would pass in on the command line
+	os.Args = split("./example get --help")
+
+	type mostNestedCmd struct {
+		Item string
+	}
+
+	type nestedCmd struct {
+		MostNested *mostNestedCmd `arg:"subcommand"`
+	}
+
+	type topLevelCmd struct {
+		Nested *nestedCmd `arg:"subcommand"`
+	}
+
+	var args struct {
+		TopLevel *topLevelCmd `arg:"subcommand"`
+	}
+
+	// This is only necessary when running inside golang's runnable example harness
+	exit := func(int) {}
+
+	p, err := NewParser(Config{Exit: exit}, &args)
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+
+	err = p.WriteHelpForSubcommand(os.Stdout, "toplevel", "nested", "mostnested")
+	if err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+
+	// output:
+	// Usage: example toplevel nested mostnested [--item ITEM]
+	//
+	// Options:
+	//   --item ITEM
+	//   --help, -h             display this help and exit
+}
+
+// This example shows the error string generated by go-arg when an invalid option is provided
+func Example_errorText() {
+	// These are the args you would pass in on the command line
+	os.Args = split("./example --optimize INVALID")
+
+	var args struct {
+		Input    string   `arg:"positional,required"`
+		Output   []string `arg:"positional"`
+		Verbose  bool     `arg:"-v" help:"verbosity level"`
+		Dataset  string   `help:"dataset to use"`
+		Optimize int      `arg:"-O,help:optimization level"`
+	}
+
+	// This is only necessary when running inside golang's runnable example harness
+	mustParseExit = func(int) {}
+
+	MustParse(&args)
+
+	// output:
+	// Usage: example [--verbose] [--dataset DATASET] [--optimize OPTIMIZE] INPUT [OUTPUT [OUTPUT ...]]
+	// error: error processing --optimize: strconv.ParseInt: parsing "INVALID": invalid syntax
+}
+
+// This example shows the error string generated by go-arg when an invalid option is provided
+func Example_errorTextForSubcommand() {
+	// These are the args you would pass in on the command line
+	os.Args = split("./example get --count INVALID")
+
+	type getCmd struct {
+		Count int
+	}
+
+	var args struct {
+		Get *getCmd `arg:"subcommand"`
+	}
+
+	// This is only necessary when running inside golang's runnable example harness
+	mustParseExit = func(int) {}
+
+	MustParse(&args)
+
+	// output:
+	// Usage: example get [--count COUNT]
+	// error: error processing --count: strconv.ParseInt: parsing "INVALID": invalid syntax
+}
+
+// This example demonstrates use of subcommands
+func Example_subcommand() {
+	// These are the args you would pass in on the command line
+	os.Args = split("./example commit -a -m what-this-commit-is-about")
+
+	type CheckoutCmd struct {
+		Branch string `arg:"positional"`
+		Track  bool   `arg:"-t"`
+	}
+	type CommitCmd struct {
+		All     bool   `arg:"-a"`
+		Message string `arg:"-m"`
+	}
+	type PushCmd struct {
+		Remote      string `arg:"positional"`
+		Branch      string `arg:"positional"`
+		SetUpstream bool   `arg:"-u"`
+	}
+	var args struct {
+		Checkout *CheckoutCmd `arg:"subcommand:checkout"`
+		Commit   *CommitCmd   `arg:"subcommand:commit"`
+		Push     *PushCmd     `arg:"subcommand:push"`
+		Quiet    bool         `arg:"-q"` // this flag is global to all subcommands
+	}
+
+	// This is only necessary when running inside golang's runnable example harness
+	mustParseExit = func(int) {}
+
+	MustParse(&args)
+
+	switch {
+	case args.Checkout != nil:
+		fmt.Printf("checkout requested for branch %s\n", args.Checkout.Branch)
+	case args.Commit != nil:
+		fmt.Printf("commit requested with message \"%s\"\n", args.Commit.Message)
+	case args.Push != nil:
+		fmt.Printf("push requested from %s to %s\n", args.Push.Branch, args.Push.Remote)
+	}
+
+	// output:
+	// commit requested with message "what-this-commit-is-about"
+}
+
+func Example_allSupportedTypes() {
+	// These are the args you would pass in on the command line
+	os.Args = []string{}
+
+	var args struct {
+		Bool     bool
+		Byte     byte
+		Rune     rune
+		Int      int
+		Int8     int8
+		Int16    int16
+		Int32    int32
+		Int64    int64
+		Float32  float32
+		Float64  float64
+		String   string
+		Duration time.Duration
+		URL      url.URL
+		Email    mail.Address
+		MAC      net.HardwareAddr
+	}
+
+	// go-arg supports each of the types above, as well as pointers to any of
+	// the above and slices of any of the above. It also supports any types that
+	// implements encoding.TextUnmarshaler.
+
+	MustParse(&args)
+
+	// output:
+}

vendor/github.com/alexflint/go-arg/go.mod

@@ -0,0 +1,14 @@
+module github.com/alexflint/go-arg
+
+require (
+	github.com/alexflint/go-scalar v1.2.0
+	github.com/stretchr/testify v1.7.0
+)
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c // indirect
+)
+
+go 1.18

vendor/github.com/alexflint/go-arg/go.sum

@@ -0,0 +1,15 @@
+github.com/alexflint/go-scalar v1.2.0 h1:WR7JPKkeNpnYIOfHRa7ivM21aWAdHD0gEWHCx+WQBRw=
+github.com/alexflint/go-scalar v1.2.0/go.mod h1:LoFvNMqS1CPrMVltza4LvnGKhaSpc3oyLEBUZVhhS2o=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
+github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

vendor/github.com/alexflint/go-arg/parse.go

@@ -5,6 +5,7 @@ import (
 	"encoding/csv"
 	"errors"
 	"fmt"
+	"io"
 	"os"
 	"path/filepath"
 	"reflect"
@@ -43,18 +44,19 @@ func (p path) Child(f reflect.StructField) path {
 
 // spec represents a command line option
 type spec struct {
-	dest        path
-	field       reflect.StructField // the struct field from which this option was created
-	long        string              // the --long form for this option, or empty if none
-	short       string              // the -s short form for this option, or empty if none
-	cardinality cardinality         // determines how many tokens will be present (possible values: zero, one, multiple)
-	required    bool                // if true, this option must be present on the command line
-	positional  bool                // if true, this option will be looked for in the positional flags
-	separate    bool                // if true, each slice and map entry will have its own --flag
-	help        string              // the help text for this option
-	env         string              // the name of the environment variable for this option, or empty for none
-	defaultVal  string              // default value for this option
-	placeholder string              // name of the data in help
+	dest          path
+	field         reflect.StructField // the struct field from which this option was created
+	long          string              // the --long form for this option, or empty if none
+	short         string              // the -s short form for this option, or empty if none
+	cardinality   cardinality         // determines how many tokens will be present (possible values: zero, one, multiple)
+	required      bool                // if true, this option must be present on the command line
+	positional    bool                // if true, this option will be looked for in the positional flags
+	separate      bool                // if true, each slice and map entry will have its own --flag
+	help          string              // the help text for this option
+	env           string              // the name of the environment variable for this option, or empty for none
+	defaultValue  reflect.Value       // default value for this option
+	defaultString string              // default value for this option, in string form to be displayed in help text
+	placeholder   string              // name of the data in help
 }
 
 // command represents a named subcommand, or the top-level command
@@ -62,38 +64,54 @@ type command struct {
 	name        string
 	help        string
 	dest        path
-	specs       []*spec
+	options     []*spec
 	subcommands []*command
+	groups      []*command
 	parent      *command
 }
 
+// specs gets all the specs from this command plus all nested option groups,
+// recursively through descendants
+func (cmd command) specs() []*spec {
+	var specs []*spec
+	specs = append(specs, cmd.options...)
+	for _, grpcmd := range cmd.groups {
+		specs = append(specs, grpcmd.specs()...)
+	}
+	return specs
+}
+
 // ErrHelp indicates that -h or --help were provided
 var ErrHelp = errors.New("help requested by user")
 
 // ErrVersion indicates that --version was provided
 var ErrVersion = errors.New("version requested by user")
 
+// for monkey patching in example code
+var mustParseExit = os.Exit
+
 // MustParse processes command line arguments and exits upon failure
 func MustParse(dest ...interface{}) *Parser {
-	p, err := NewParser(Config{}, dest...)
+	return mustParse(Config{Exit: mustParseExit}, dest...)
+}
+
+// mustParse is a helper that facilitates testing
+func mustParse(config Config, dest ...interface{}) *Parser {
+	if config.Exit == nil {
+		config.Exit = os.Exit
+	}
+	if config.Out == nil {
+		config.Out = os.Stdout
+	}
+
+	p, err := NewParser(config, dest...)
 	if err != nil {
-		fmt.Fprintln(stdout, err)
-		osExit(-1)
-		return nil // just in case osExit was monkey-patched
-	}
-
-	err = p.Parse(flags())
-	switch {
-	case err == ErrHelp:
-		p.writeHelpForSubcommand(stdout, p.lastCmd)
-		osExit(0)
-	case err == ErrVersion:
-		fmt.Fprintln(stdout, p.version)
-		osExit(0)
-	case err != nil:
-		p.failWithSubcommand(err.Error(), p.lastCmd)
+		fmt.Fprintln(config.Out, err)
+		config.Exit(-1)
+		return nil
 	}
 
+	p.MustParse(flags())
 	return p
 }
 
@@ -121,6 +139,20 @@ type Config struct {
 
 	// IgnoreEnv instructs the library not to read environment variables
 	IgnoreEnv bool
+
+	// IgnoreDefault instructs the library not to reset the variables to the
+	// default values, including pointers to sub commands
+	IgnoreDefault bool
+
+	// StrictSubcommands intructs the library not to allow global commands after
+	// subcommand
+	StrictSubcommands bool
+
+	// Exit is called to terminate the process with an error code (defaults to os.Exit)
+	Exit func(int)
+
+	// Out is where help text, usage text, and failure messages are printed (defaults to os.Stdout)
+	Out io.Writer
 }
 
 // Parser represents a set of command line options with destination values
@@ -130,6 +162,7 @@ type Parser struct {
 	config      Config
 	version     string
 	description string
+	epilogue    string
 
 	// the following field changes during processing of command line arguments
 	lastCmd *command
@@ -151,6 +184,14 @@ type Described interface {
 	Description() string
 }
 
+// Epilogued is the interface that the destination struct should implement to
+// add an epilogue string at the bottom of the help message.
+type Epilogued interface {
+	// Epilogue returns the string that will be printed on a line by itself
+	// at the end of the help message.
+	Epilogue() string
+}
+
 // walkFields calls a function for each field of a struct, recursively expanding struct fields.
 func walkFields(t reflect.Type, visit func(field reflect.StructField, owner reflect.Type) bool) {
 	walkFieldsImpl(t, visit, nil)
@@ -174,6 +215,14 @@ func walkFieldsImpl(t reflect.Type, visit func(field reflect.StructField, owner
 
 // NewParser constructs a parser from a list of destination structs
 func NewParser(config Config, dests ...interface{}) (*Parser, error) {
+	// fill in defaults
+	if config.Exit == nil {
+		config.Exit = os.Exit
+	}
+	if config.Out == nil {
+		config.Out = os.Stdout
+	}
+
 	// first pick a name for the command for use in the usage text
 	var name string
 	switch {
@@ -197,34 +246,36 @@ func NewParser(config Config, dests ...interface{}) (*Parser, error) {
 	}
 
 	// process each of the destination values
-	for i, dest := range dests {
+	for _, dest := range dests {
 		t := reflect.TypeOf(dest)
 		if t.Kind() != reflect.Ptr {
 			panic(fmt.Sprintf("%s is not a pointer (did you forget an ampersand?)", t))
 		}
 
-		cmd, err := cmdFromStruct(name, path{root: i}, t)
+		err := p.cmd.parseFieldsFromStructPointer(t, false)
 		if err != nil {
 			return nil, err
 		}
 
-		// add nonzero field values as defaults
-		for _, spec := range cmd.specs {
-			if v := p.val(spec.dest); v.IsValid() && !isZero(v) {
-				if defaultVal, ok := v.Interface().(encoding.TextMarshaler); ok {
-					str, err := defaultVal.MarshalText()
-					if err != nil {
-						return nil, fmt.Errorf("%v: error marshaling default value to string: %v", spec.dest, err)
-					}
-					spec.defaultVal = string(str)
-				} else {
-					spec.defaultVal = fmt.Sprintf("%v", v)
-				}
+		// for backwards compatibility, add nonzero field values as defaults
+		// this applies only to the top-level command, not to subcommands (this inconsistency
+		// is the reason that this method for setting default values was deprecated)
+		for _, spec := range p.cmd.specs() {
+			// get the value
+			defaultString, defaultValue, err := p.defaultVal(spec.dest)
+			if err != nil {
+				return nil, err
 			}
-		}
 
-		p.cmd.specs = append(p.cmd.specs, cmd.specs...)
-		p.cmd.subcommands = append(p.cmd.subcommands, cmd.subcommands...)
+			// if the value is the "zero value" (e.g. nil pointer, empty struct) then ignore
+			if defaultString == "" {
+				continue
+			}
+
+			// store as a default
+			spec.defaultString = defaultString
+			spec.defaultValue = defaultValue
+		}
 
 		if dest, ok := dest.(Versioned); ok {
 			p.version = dest.Version()
@@ -232,29 +283,56 @@ func NewParser(config Config, dests ...interface{}) (*Parser, error) {
 		if dest, ok := dest.(Described); ok {
 			p.description = dest.Description()
 		}
+		if dest, ok := dest.(Epilogued); ok {
+			p.epilogue = dest.Epilogue()
+		}
 	}
 
 	return &p, nil
 }
 
-func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
+// parseFieldsFromStructPointer ensures the destination structure is a pointer
+// to a struct. This function should be called when parsing commands or
+// subcommands as they can only be a struct pointer.
+func (cmd *command) parseFieldsFromStructPointer(t reflect.Type, insideGroup bool) error {
 	// commands can only be created from pointers to structs
 	if t.Kind() != reflect.Ptr {
-		return nil, fmt.Errorf("subcommands must be pointers to structs but %s is a %s",
-			dest, t.Kind())
+		return fmt.Errorf("subcommands must be pointers to structs but %s is a %s",
+			cmd.dest, t.Kind())
 	}
 
 	t = t.Elem()
 	if t.Kind() != reflect.Struct {
-		return nil, fmt.Errorf("subcommands must be pointers to structs but %s is a pointer to %s",
-			dest, t.Kind())
+		return fmt.Errorf("subcommands must be pointers to structs but %s is a pointer to %s",
+			cmd.dest, t.Kind())
+	}
+	return cmd.parseStruct(t, insideGroup)
+}
+
+// parseFieldsFromStructOrStructPointer ensures the destination structure is
+// either a pointer to a struct, or a struct. This function should be called
+// when parsing option groups as they can only be a struct, or a pointer to one.
+func (cmd *command) parseFieldsFromStructOrStructPointer(t reflect.Type, insideGroup bool) error {
+	// option groups can only be created from structs or pointers to structs
+	typeHint := ""
+	if t.Kind() == reflect.Ptr {
+		typeHint = "a pointer to "
+		t = t.Elem()
 	}
 
-	cmd := command{
-		name: name,
-		dest: dest,
+	if t.Kind() != reflect.Struct {
+		return fmt.Errorf("option groups must be structs or pointers to structs, but %s is %s%s",
+			cmd.dest, typeHint, t.Kind())
 	}
 
+	return cmd.parseStruct(t, insideGroup)
+}
+
+// parseStruct populates the command instance based on the type and annotations
+// of the target struct. As these command instances are used for either (sub)
+// commands or option groups, please refer to the parseFieldsFromStructPointer
+// or parseFieldsFromStructOrStructPointer respectively.
+func (cmd *command) parseStruct(t reflect.Type, insideGroup bool) error {
 	var errs []string
 	walkFields(t, func(field reflect.StructField, t reflect.Type) bool {
 		// check for the ignore switch in the tag
@@ -276,7 +354,7 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 		}
 
 		// duplicate the entire path to avoid slice overwrites
-		subdest := dest.Child(field)
+		subdest := cmd.dest.Child(field)
 		spec := spec{
 			dest:  subdest,
 			field: field,
@@ -288,13 +366,7 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 			spec.help = help
 		}
 
-		defaultVal, hasDefault := field.Tag.Lookup("default")
-		if hasDefault {
-			spec.defaultVal = defaultVal
-		}
-
 		// Look at the tag
-		var isSubcommand bool // tracks whether this field is a subcommand
 		for _, key := range strings.Split(tag, ",") {
 			if key == "" {
 				continue
@@ -319,11 +391,6 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 				}
 				spec.short = key[1:]
 			case key == "required":
-				if hasDefault {
-					errs = append(errs, fmt.Sprintf("%s.%s: 'required' cannot be used when a default value is specified",
-						t.Name(), field.Name))
-					return false
-				}
 				spec.required = true
 			case key == "positional":
 				spec.positional = true
@@ -339,24 +406,55 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 					spec.env = strings.ToUpper(field.Name)
 				}
 			case key == "subcommand":
+				subCmd := command{
+					name:   value,
+					dest:   subdest,
+					parent: cmd,
+					help:   field.Tag.Get("help"),
+				}
+				cmd.subcommands = append(cmd.subcommands, &subCmd)
+
+				if insideGroup {
+					errs = append(errs, fmt.Sprintf("%s.%s: %s subcommands cannot be part of option groups",
+						t.Name(), field.Name, field.Type.String()))
+					return false
+				}
+
 				// decide on a name for the subcommand
-				cmdname := value
-				if cmdname == "" {
-					cmdname = strings.ToLower(field.Name)
+				if subCmd.name == "" {
+					subCmd.name = strings.ToLower(field.Name)
 				}
 
 				// parse the subcommand recursively
-				subcmd, err := cmdFromStruct(cmdname, subdest, field.Type)
+				err := subCmd.parseFieldsFromStructPointer(field.Type, false)
 				if err != nil {
 					errs = append(errs, err.Error())
 					return false
 				}
 
-				subcmd.parent = &cmd
-				subcmd.help = field.Tag.Get("help")
+				return true
+			case key == "group":
+				// parse the option group recursively
+				optGrp := command{
+					name:   value,
+					dest:   subdest,
+					parent: cmd,
+					help:   field.Tag.Get("help"),
+				}
+				cmd.groups = append(cmd.groups, &optGrp)
 
-				cmd.subcommands = append(cmd.subcommands, subcmd)
-				isSubcommand = true
+				// decide on a name for the group
+				if optGrp.name == "" {
+					optGrp.name = strings.Title(field.Name)
+				}
+
+				err := optGrp.parseFieldsFromStructOrStructPointer(field.Type, true)
+				if err != nil {
+					errs = append(errs, err.Error())
+					return false
+				}
+
+				return false
 			default:
 				errs = append(errs, fmt.Sprintf("unrecognized tag '%s' on field %s", key, tag))
 				return false
@@ -372,47 +470,77 @@ func cmdFromStruct(name string, dest path, t reflect.Type) (*command, error) {
 			spec.placeholder = strings.ToUpper(spec.field.Name)
 		}
 
-		// Check whether this field is supported. It's good to do this here rather than
+		// check whether this field is supported. It's good to do this here rather than
 		// wait until ParseValue because it means that a program with invalid argument
 		// fields will always fail regardless of whether the arguments it received
 		// exercised those fields.
-		if !isSubcommand {
-			cmd.specs = append(cmd.specs, &spec)
+		var err error
+		spec.cardinality, err = cardinalityOf(field.Type)
+		if err != nil {
+			errs = append(errs, fmt.Sprintf("%s.%s: %s fields are not supported",
+				t.Name(), field.Name, field.Type.String()))
+			return false
+		}
 
-			var err error
-			spec.cardinality, err = cardinalityOf(field.Type)
-			if err != nil {
-				errs = append(errs, fmt.Sprintf("%s.%s: %s fields are not supported",
-					t.Name(), field.Name, field.Type.String()))
-				return false
-			}
-			if spec.cardinality == multiple && hasDefault {
+		defaultString, hasDefault := field.Tag.Lookup("default")
+		if hasDefault {
+			// we do not support default values for maps and slices
+			if spec.cardinality == multiple {
 				errs = append(errs, fmt.Sprintf("%s.%s: default values are not supported for slice or map fields",
 					t.Name(), field.Name))
 				return false
 			}
+
+			// a required field cannot also have a default value
+			if spec.required {
+				errs = append(errs, fmt.Sprintf("%s.%s: 'required' cannot be used when a default value is specified",
+					t.Name(), field.Name))
+				return false
+			}
+
+			// parse the default value
+			spec.defaultString = defaultString
+			if field.Type.Kind() == reflect.Ptr {
+				// here we have a field of type *T and we create a new T, no need to dereference
+				// in order for the value to be settable
+				spec.defaultValue = reflect.New(field.Type.Elem())
+			} else {
+				// here we have a field of type T and we create a new T and then dereference it
+				// so that the resulting value is settable
+				spec.defaultValue = reflect.New(field.Type).Elem()
+			}
+			err := scalar.ParseValue(spec.defaultValue, defaultString)
+			if err != nil {
+				errs = append(errs, fmt.Sprintf("%s.%s: error processing default value: %v", t.Name(), field.Name, err))
+				return false
+			}
 		}
 
+		// add the spec to the list of specs
+		cmd.options = append(cmd.options, &spec)
+
 		// if this was an embedded field then we already returned true up above
 		return false
 	})
 
 	if len(errs) > 0 {
-		return nil, errors.New(strings.Join(errs, "\n"))
+		return errors.New(strings.Join(errs, "\n"))
 	}
 
 	// check that we don't have both positionals and subcommands
 	var hasPositional bool
-	for _, spec := range cmd.specs {
+	for _, spec := range cmd.options {
 		if spec.positional {
 			hasPositional = true
 		}
 	}
 	if hasPositional && len(cmd.subcommands) > 0 {
-		return nil, fmt.Errorf("%s cannot have both subcommands and positional arguments", dest)
+		return fmt.Errorf("%s cannot have both subcommands and positional arguments",
+			cmd.dest)
+
 	}
 
-	return &cmd, nil
+	return nil
 }
 
 // Parse processes the given command line option, storing the results in the field
@@ -433,6 +561,20 @@ func (p *Parser) Parse(args []string) error {
 	return err
 }
 
+func (p *Parser) MustParse(args []string) {
+	err := p.Parse(args)
+	switch {
+	case err == ErrHelp:
+		p.writeHelpForSubcommand(p.config.Out, p.lastCmd)
+		p.config.Exit(0)
+	case err == ErrVersion:
+		fmt.Fprintln(p.config.Out, p.version)
+		p.config.Exit(0)
+	case err != nil:
+		p.failWithSubcommand(err.Error(), p.lastCmd)
+	}
+}
+
 // process environment vars for the given arguments
 func (p *Parser) captureEnvVars(specs []*spec, wasPresent map[*spec]bool) error {
 	for _, spec := range specs {
@@ -489,8 +631,7 @@ func (p *Parser) process(args []string) error {
 	p.lastCmd = curCmd
 
 	// make a copy of the specs because we will add to this list each time we expand a subcommand
-	specs := make([]*spec, len(curCmd.specs))
-	copy(specs, curCmd.specs)
+	specs := curCmd.specs()
 
 	// deal with environment vars
 	if !p.config.IgnoreEnv {
@@ -525,16 +666,20 @@ func (p *Parser) process(args []string) error {
 				return fmt.Errorf("invalid subcommand: %s", arg)
 			}
 
-			// instantiate the field to point to a new struct
-			v := p.val(subcmd.dest)
-			v.Set(reflect.New(v.Type().Elem())) // we already checked that all subcommands are struct pointers
+			// ensure the command struct exists (is not a nil pointer)
+			p.val(subcmd.dest)
 
 			// add the new options to the set of allowed options
-			specs = append(specs, subcmd.specs...)
+			if p.config.StrictSubcommands {
+				specs = make([]*spec, len(subcmd.specs()))
+				copy(specs, subcmd.specs())
+			} else {
+				specs = append(specs, subcmd.specs()...)
+			}
 
 			// capture environment vars for these new options
 			if !p.config.IgnoreEnv {
-				err := p.captureEnvVars(subcmd.specs, wasPresent)
+				err := p.captureEnvVars(subcmd.specs(), wasPresent)
 				if err != nil {
 					return err
 				}
@@ -659,11 +804,14 @@ func (p *Parser) process(args []string) error {
 			}
 			return errors.New(msg)
 		}
-		if spec.defaultVal != "" {
-			err := scalar.ParseValue(p.val(spec.dest), spec.defaultVal)
-			if err != nil {
-				return fmt.Errorf("error processing default value for %s: %v", name, err)
-			}
+
+		if spec.defaultValue.IsValid() && !p.config.IgnoreDefault {
+			// One issue here is that if the user now modifies the value then
+			// the default value stored in the spec will be corrupted. There
+			// is no general way to "deep-copy" values in Go, and we still
+			// support the old-style method for specifying defaults as
+			// Go values assigned directly to the struct field, so we are stuck.
+			p.val(spec.dest).Set(spec.defaultValue)
 		}
 	}
 
@@ -688,20 +836,57 @@ func isFlag(s string) bool {
 	return strings.HasPrefix(s, "-") && strings.TrimLeft(s, "-") != ""
 }
 
-// val returns a reflect.Value corresponding to the current value for the
-// given path
-func (p *Parser) val(dest path) reflect.Value {
+// defaultVal returns the string representation of the value at dest if it is
+// reachable without traversing nil pointers, but only if it does not represent
+// the default value for the type.
+func (p *Parser) defaultVal(dest path) (string, reflect.Value, error) {
 	v := p.roots[dest.root]
 	for _, field := range dest.fields {
 		if v.Kind() == reflect.Ptr {
 			if v.IsNil() {
-				return reflect.Value{}
+				return "", v, nil
 			}
 			v = v.Elem()
 		}
 
 		v = v.FieldByIndex(field.Index)
 	}
+
+	if !v.IsValid() || isZero(v) {
+		return "", v, nil
+	}
+
+	if defaultVal, ok := v.Interface().(encoding.TextMarshaler); ok {
+		str, err := defaultVal.MarshalText()
+		if err != nil {
+			return "", v, fmt.Errorf("%v: error marshaling default value to string: %w", dest, err)
+		}
+		return string(str), v, nil
+	}
+
+	return fmt.Sprintf("%v", v), v, nil
+}
+
+// val returns a reflect.Value corresponding to the current value for the
+// given path initiating nil pointers in the path
+func (p *Parser) val(dest path) reflect.Value {
+	v := p.roots[dest.root]
+	for _, field := range dest.fields {
+		if v.Kind() == reflect.Ptr {
+			if v.IsNil() {
+				v.Set(reflect.New(v.Type().Elem()))
+			}
+			v = v.Elem()
+		}
+
+		v = v.FieldByIndex(field.Index)
+	}
+
+	// Don't return a nil-pointer
+	if v.Kind() == reflect.Ptr && v.IsNil() {
+		v.Set(reflect.New(v.Type().Elem()))
+	}
+
 	return v
 }
 

vendor/github.com/alexflint/go-arg/reflect.go

@@ -13,9 +13,9 @@ import (
 var textUnmarshalerType = reflect.TypeOf([]encoding.TextUnmarshaler{}).Elem()
 
 // cardinality tracks how many tokens are expected for a given spec
-//  - zero is a boolean, which does to expect any value
-//  - one is an ordinary option that will be parsed from a single token
-//  - multiple is a slice or map that can accept zero or more tokens
+//   - zero is a boolean, which does to expect any value
+//   - one is an ordinary option that will be parsed from a single token
+//   - multiple is a slice or map that can accept zero or more tokens
 type cardinality int
 
 const (
@@ -74,10 +74,10 @@ func cardinalityOf(t reflect.Type) (cardinality, error) {
 	}
 }
 
-// isBoolean returns true if the type can be parsed from a single string
+// isBoolean returns true if the type is a boolean or a pointer to a boolean
 func isBoolean(t reflect.Type) bool {
 	switch {
-	case t.Implements(textUnmarshalerType):
+	case isTextUnmarshaler(t):
 		return false
 	case t.Kind() == reflect.Bool:
 		return true
@@ -88,6 +88,11 @@ func isBoolean(t reflect.Type) bool {
 	}
 }
 
+// isTextUnmarshaler returns true if the type or its pointer implements encoding.TextUnmarshaler
+func isTextUnmarshaler(t reflect.Type) bool {
+	return t.Implements(textUnmarshalerType) || reflect.PtrTo(t).Implements(textUnmarshalerType)
+}
+
 // isExported returns true if the struct field name is exported
 func isExported(field string) bool {
 	r, _ := utf8.DecodeRuneInString(field) // returns RuneError for empty string or invalid UTF8
@@ -97,7 +102,7 @@ func isExported(field string) bool {
 // isZero returns true if v contains the zero value for its type
 func isZero(v reflect.Value) bool {
 	t := v.Type()
-	if t.Kind() == reflect.Slice || t.Kind() == reflect.Map {
+	if t.Kind() == reflect.Ptr || t.Kind() == reflect.Slice || t.Kind() == reflect.Map || t.Kind() == reflect.Chan || t.Kind() == reflect.Interface {
 		return v.IsNil()
 	}
 	if !t.Comparable() {

vendor/github.com/alexflint/go-arg/reflect_test.go

@@ -0,0 +1,112 @@
+package arg
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func assertCardinality(t *testing.T, typ reflect.Type, expected cardinality) {
+	actual, err := cardinalityOf(typ)
+	assert.Equal(t, expected, actual, "expected %v to have cardinality %v but got %v", typ, expected, actual)
+	if expected == unsupported {
+		assert.Error(t, err)
+	}
+}
+
+func TestCardinalityOf(t *testing.T) {
+	var b bool
+	var i int
+	var s string
+	var f float64
+	var bs []bool
+	var is []int
+	var m map[string]int
+	var unsupported1 struct{}
+	var unsupported2 []struct{}
+	var unsupported3 map[string]struct{}
+	var unsupported4 map[struct{}]string
+
+	assertCardinality(t, reflect.TypeOf(b), zero)
+	assertCardinality(t, reflect.TypeOf(i), one)
+	assertCardinality(t, reflect.TypeOf(s), one)
+	assertCardinality(t, reflect.TypeOf(f), one)
+
+	assertCardinality(t, reflect.TypeOf(&b), zero)
+	assertCardinality(t, reflect.TypeOf(&s), one)
+	assertCardinality(t, reflect.TypeOf(&i), one)
+	assertCardinality(t, reflect.TypeOf(&f), one)
+
+	assertCardinality(t, reflect.TypeOf(bs), multiple)
+	assertCardinality(t, reflect.TypeOf(is), multiple)
+
+	assertCardinality(t, reflect.TypeOf(&bs), multiple)
+	assertCardinality(t, reflect.TypeOf(&is), multiple)
+
+	assertCardinality(t, reflect.TypeOf(m), multiple)
+	assertCardinality(t, reflect.TypeOf(&m), multiple)
+
+	assertCardinality(t, reflect.TypeOf(unsupported1), unsupported)
+	assertCardinality(t, reflect.TypeOf(&unsupported1), unsupported)
+	assertCardinality(t, reflect.TypeOf(unsupported2), unsupported)
+	assertCardinality(t, reflect.TypeOf(&unsupported2), unsupported)
+	assertCardinality(t, reflect.TypeOf(unsupported3), unsupported)
+	assertCardinality(t, reflect.TypeOf(&unsupported3), unsupported)
+	assertCardinality(t, reflect.TypeOf(unsupported4), unsupported)
+	assertCardinality(t, reflect.TypeOf(&unsupported4), unsupported)
+}
+
+type implementsTextUnmarshaler struct{}
+
+func (*implementsTextUnmarshaler) UnmarshalText(text []byte) error {
+	return nil
+}
+
+func TestCardinalityTextUnmarshaler(t *testing.T) {
+	var x implementsTextUnmarshaler
+	var s []implementsTextUnmarshaler
+	var m []implementsTextUnmarshaler
+	assertCardinality(t, reflect.TypeOf(x), one)
+	assertCardinality(t, reflect.TypeOf(&x), one)
+	assertCardinality(t, reflect.TypeOf(s), multiple)
+	assertCardinality(t, reflect.TypeOf(&s), multiple)
+	assertCardinality(t, reflect.TypeOf(m), multiple)
+	assertCardinality(t, reflect.TypeOf(&m), multiple)
+}
+
+func TestIsExported(t *testing.T) {
+	assert.True(t, isExported("Exported"))
+	assert.False(t, isExported("notExported"))
+	assert.False(t, isExported(""))
+	assert.False(t, isExported(string([]byte{255})))
+}
+
+func TestCardinalityString(t *testing.T) {
+	assert.Equal(t, "zero", zero.String())
+	assert.Equal(t, "one", one.String())
+	assert.Equal(t, "multiple", multiple.String())
+	assert.Equal(t, "unsupported", unsupported.String())
+	assert.Equal(t, "unknown(42)", cardinality(42).String())
+}
+
+func TestIsZero(t *testing.T) {
+	var zero int
+	var notZero = 3
+	var nilSlice []int
+	var nonNilSlice = []int{1, 2, 3}
+	var nilMap map[string]string
+	var nonNilMap = map[string]string{"foo": "bar"}
+	var uncomparable = func() {}
+
+	assert.True(t, isZero(reflect.ValueOf(zero)))
+	assert.False(t, isZero(reflect.ValueOf(notZero)))
+
+	assert.True(t, isZero(reflect.ValueOf(nilSlice)))
+	assert.False(t, isZero(reflect.ValueOf(nonNilSlice)))
+
+	assert.True(t, isZero(reflect.ValueOf(nilMap)))
+	assert.False(t, isZero(reflect.ValueOf(nonNilMap)))
+
+	assert.False(t, isZero(reflect.ValueOf(uncomparable)))
+}

vendor/github.com/alexflint/go-arg/sequence_test.go

@@ -0,0 +1,152 @@
+package arg
+
+import (
+	"reflect"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSetSliceWithoutClearing(t *testing.T) {
+	xs := []int{10}
+	entries := []string{"1", "2", "3"}
+	err := setSlice(reflect.ValueOf(&xs).Elem(), entries, false)
+	require.NoError(t, err)
+	assert.Equal(t, []int{10, 1, 2, 3}, xs)
+}
+
+func TestSetSliceAfterClearing(t *testing.T) {
+	xs := []int{100}
+	entries := []string{"1", "2", "3"}
+	err := setSlice(reflect.ValueOf(&xs).Elem(), entries, true)
+	require.NoError(t, err)
+	assert.Equal(t, []int{1, 2, 3}, xs)
+}
+
+func TestSetSliceInvalid(t *testing.T) {
+	xs := []int{100}
+	entries := []string{"invalid"}
+	err := setSlice(reflect.ValueOf(&xs).Elem(), entries, true)
+	assert.Error(t, err)
+}
+
+func TestSetSlicePtr(t *testing.T) {
+	var xs []*int
+	entries := []string{"1", "2", "3"}
+	err := setSlice(reflect.ValueOf(&xs).Elem(), entries, true)
+	require.NoError(t, err)
+	require.Len(t, xs, 3)
+	assert.Equal(t, 1, *xs[0])
+	assert.Equal(t, 2, *xs[1])
+	assert.Equal(t, 3, *xs[2])
+}
+
+func TestSetSliceTextUnmarshaller(t *testing.T) {
+	// textUnmarshaler is a struct that captures the length of the string passed to it
+	var xs []*textUnmarshaler
+	entries := []string{"a", "aa", "aaa"}
+	err := setSlice(reflect.ValueOf(&xs).Elem(), entries, true)
+	require.NoError(t, err)
+	require.Len(t, xs, 3)
+	assert.Equal(t, 1, xs[0].val)
+	assert.Equal(t, 2, xs[1].val)
+	assert.Equal(t, 3, xs[2].val)
+}
+
+func TestSetMapWithoutClearing(t *testing.T) {
+	m := map[string]int{"foo": 10}
+	entries := []string{"a=1", "b=2"}
+	err := setMap(reflect.ValueOf(&m).Elem(), entries, false)
+	require.NoError(t, err)
+	require.Len(t, m, 3)
+	assert.Equal(t, 1, m["a"])
+	assert.Equal(t, 2, m["b"])
+	assert.Equal(t, 10, m["foo"])
+}
+
+func TestSetMapAfterClearing(t *testing.T) {
+	m := map[string]int{"foo": 10}
+	entries := []string{"a=1", "b=2"}
+	err := setMap(reflect.ValueOf(&m).Elem(), entries, true)
+	require.NoError(t, err)
+	require.Len(t, m, 2)
+	assert.Equal(t, 1, m["a"])
+	assert.Equal(t, 2, m["b"])
+}
+
+func TestSetMapWithKeyPointer(t *testing.T) {
+	// textUnmarshaler is a struct that captures the length of the string passed to it
+	var m map[*string]int
+	entries := []string{"abc=123"}
+	err := setMap(reflect.ValueOf(&m).Elem(), entries, true)
+	require.NoError(t, err)
+	require.Len(t, m, 1)
+}
+
+func TestSetMapWithValuePointer(t *testing.T) {
+	// textUnmarshaler is a struct that captures the length of the string passed to it
+	var m map[string]*int
+	entries := []string{"abc=123"}
+	err := setMap(reflect.ValueOf(&m).Elem(), entries, true)
+	require.NoError(t, err)
+	require.Len(t, m, 1)
+	assert.Equal(t, 123, *m["abc"])
+}
+
+func TestSetMapTextUnmarshaller(t *testing.T) {
+	// textUnmarshaler is a struct that captures the length of the string passed to it
+	var m map[textUnmarshaler]*textUnmarshaler
+	entries := []string{"a=123", "aa=12", "aaa=1"}
+	err := setMap(reflect.ValueOf(&m).Elem(), entries, true)
+	require.NoError(t, err)
+	require.Len(t, m, 3)
+	assert.Equal(t, &textUnmarshaler{3}, m[textUnmarshaler{1}])
+	assert.Equal(t, &textUnmarshaler{2}, m[textUnmarshaler{2}])
+	assert.Equal(t, &textUnmarshaler{1}, m[textUnmarshaler{3}])
+}
+
+func TestSetMapInvalidKey(t *testing.T) {
+	var m map[int]int
+	entries := []string{"invalid=123"}
+	err := setMap(reflect.ValueOf(&m).Elem(), entries, true)
+	assert.Error(t, err)
+}
+
+func TestSetMapInvalidValue(t *testing.T) {
+	var m map[int]int
+	entries := []string{"123=invalid"}
+	err := setMap(reflect.ValueOf(&m).Elem(), entries, true)
+	assert.Error(t, err)
+}
+
+func TestSetMapMalformed(t *testing.T) {
+	// textUnmarshaler is a struct that captures the length of the string passed to it
+	var m map[string]string
+	entries := []string{"missing_equals_sign"}
+	err := setMap(reflect.ValueOf(&m).Elem(), entries, true)
+	assert.Error(t, err)
+}
+
+func TestSetSliceOrMapErrors(t *testing.T) {
+	var err error
+	var dest reflect.Value
+
+	// converting a slice to a reflect.Value in this way will make it read only
+	var cannotSet []int
+	dest = reflect.ValueOf(cannotSet)
+	err = setSliceOrMap(dest, nil, false)
+	assert.Error(t, err)
+
+	// check what happens when we pass in something that is not a slice or a map
+	var notSliceOrMap string
+	dest = reflect.ValueOf(&notSliceOrMap).Elem()
+	err = setSliceOrMap(dest, nil, false)
+	assert.Error(t, err)
+
+	// check what happens when we pass in a pointer to something that is not a slice or a map
+	var stringPtr *string
+	dest = reflect.ValueOf(&stringPtr).Elem()
+	err = setSliceOrMap(dest, nil, false)
+	assert.Error(t, err)
+}

vendor/github.com/alexflint/go-arg/subcommand_test.go

@@ -0,0 +1,408 @@
+package arg
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+// This file contains tests for parse.go but I decided to put them here
+// since that file is getting large
+
+func TestSubcommandNotAPointer(t *testing.T) {
+	var args struct {
+		A string `arg:"subcommand"`
+	}
+	_, err := NewParser(Config{}, &args)
+	assert.Error(t, err)
+}
+
+func TestSubcommandNotAPointerToStruct(t *testing.T) {
+	var args struct {
+		A struct{} `arg:"subcommand"`
+	}
+	_, err := NewParser(Config{}, &args)
+	assert.Error(t, err)
+}
+
+func TestPositionalAndSubcommandNotAllowed(t *testing.T) {
+	var args struct {
+		A string    `arg:"positional"`
+		B *struct{} `arg:"subcommand"`
+	}
+	_, err := NewParser(Config{}, &args)
+	assert.Error(t, err)
+}
+
+func TestMinimalSubcommand(t *testing.T) {
+	type listCmd struct {
+	}
+	var args struct {
+		List *listCmd `arg:"subcommand"`
+	}
+	p, err := pparse("list", &args)
+	require.NoError(t, err)
+	assert.NotNil(t, args.List)
+	assert.Equal(t, args.List, p.Subcommand())
+	assert.Equal(t, []string{"list"}, p.SubcommandNames())
+}
+
+func TestSubcommandNamesBeforeParsing(t *testing.T) {
+	type listCmd struct{}
+	var args struct {
+		List *listCmd `arg:"subcommand"`
+	}
+	p, err := NewParser(Config{}, &args)
+	require.NoError(t, err)
+	assert.Nil(t, p.Subcommand())
+	assert.Nil(t, p.SubcommandNames())
+}
+
+func TestNoSuchSubcommand(t *testing.T) {
+	type listCmd struct {
+	}
+	var args struct {
+		List *listCmd `arg:"subcommand"`
+	}
+	_, err := pparse("invalid", &args)
+	assert.Error(t, err)
+}
+
+func TestNamedSubcommand(t *testing.T) {
+	type listCmd struct {
+	}
+	var args struct {
+		List *listCmd `arg:"subcommand:ls"`
+	}
+	p, err := pparse("ls", &args)
+	require.NoError(t, err)
+	assert.NotNil(t, args.List)
+	assert.Equal(t, args.List, p.Subcommand())
+	assert.Equal(t, []string{"ls"}, p.SubcommandNames())
+}
+
+func TestEmptySubcommand(t *testing.T) {
+	type listCmd struct {
+	}
+	var args struct {
+		List *listCmd `arg:"subcommand"`
+	}
+	p, err := pparse("", &args)
+	require.NoError(t, err)
+	assert.Nil(t, args.List)
+	assert.Nil(t, p.Subcommand())
+	assert.Empty(t, p.SubcommandNames())
+}
+
+func TestTwoSubcommands(t *testing.T) {
+	type getCmd struct {
+	}
+	type listCmd struct {
+	}
+	var args struct {
+		Get  *getCmd  `arg:"subcommand"`
+		List *listCmd `arg:"subcommand"`
+	}
+	p, err := pparse("list", &args)
+	require.NoError(t, err)
+	assert.Nil(t, args.Get)
+	assert.NotNil(t, args.List)
+	assert.Equal(t, args.List, p.Subcommand())
+	assert.Equal(t, []string{"list"}, p.SubcommandNames())
+}
+
+func TestSubcommandsWithOptions(t *testing.T) {
+	type getCmd struct {
+		Name string
+	}
+	type listCmd struct {
+		Limit int
+	}
+	type cmd struct {
+		Verbose bool
+		Get     *getCmd  `arg:"subcommand"`
+		List    *listCmd `arg:"subcommand"`
+	}
+
+	{
+		var args cmd
+		err := parse("list", &args)
+		require.NoError(t, err)
+		assert.Nil(t, args.Get)
+		assert.NotNil(t, args.List)
+	}
+
+	{
+		var args cmd
+		err := parse("list --limit 3", &args)
+		require.NoError(t, err)
+		assert.Nil(t, args.Get)
+		assert.NotNil(t, args.List)
+		assert.Equal(t, args.List.Limit, 3)
+	}
+
+	{
+		var args cmd
+		err := parse("list --limit 3 --verbose", &args)
+		require.NoError(t, err)
+		assert.Nil(t, args.Get)
+		assert.NotNil(t, args.List)
+		assert.Equal(t, args.List.Limit, 3)
+		assert.True(t, args.Verbose)
+	}
+
+	{
+		var args cmd
+		err := parse("list --verbose --limit 3", &args)
+		require.NoError(t, err)
+		assert.Nil(t, args.Get)
+		assert.NotNil(t, args.List)
+		assert.Equal(t, args.List.Limit, 3)
+		assert.True(t, args.Verbose)
+	}
+
+	{
+		var args cmd
+		err := parse("--verbose list --limit 3", &args)
+		require.NoError(t, err)
+		assert.Nil(t, args.Get)
+		assert.NotNil(t, args.List)
+		assert.Equal(t, args.List.Limit, 3)
+		assert.True(t, args.Verbose)
+	}
+
+	{
+		var args cmd
+		err := parse("get", &args)
+		require.NoError(t, err)
+		assert.NotNil(t, args.Get)
+		assert.Nil(t, args.List)
+	}
+
+	{
+		var args cmd
+		err := parse("get --name test", &args)
+		require.NoError(t, err)
+		assert.NotNil(t, args.Get)
+		assert.Nil(t, args.List)
+		assert.Equal(t, args.Get.Name, "test")
+	}
+}
+
+func TestSubcommandsWithEnvVars(t *testing.T) {
+	type getCmd struct {
+		Name string `arg:"env"`
+	}
+	type listCmd struct {
+		Limit int `arg:"env"`
+	}
+	type cmd struct {
+		Verbose bool
+		Get     *getCmd  `arg:"subcommand"`
+		List    *listCmd `arg:"subcommand"`
+	}
+
+	{
+		var args cmd
+		setenv(t, "LIMIT", "123")
+		err := parse("list", &args)
+		require.NoError(t, err)
+		require.NotNil(t, args.List)
+		assert.Equal(t, 123, args.List.Limit)
+	}
+
+	{
+		var args cmd
+		setenv(t, "LIMIT", "not_an_integer")
+		err := parse("list", &args)
+		assert.Error(t, err)
+	}
+}
+
+func TestNestedSubcommands(t *testing.T) {
+	type child struct{}
+	type parent struct {
+		Child *child `arg:"subcommand"`
+	}
+	type grandparent struct {
+		Parent *parent `arg:"subcommand"`
+	}
+	type root struct {
+		Grandparent *grandparent `arg:"subcommand"`
+	}
+
+	{
+		var args root
+		p, err := pparse("grandparent parent child", &args)
+		require.NoError(t, err)
+		require.NotNil(t, args.Grandparent)
+		require.NotNil(t, args.Grandparent.Parent)
+		require.NotNil(t, args.Grandparent.Parent.Child)
+		assert.Equal(t, args.Grandparent.Parent.Child, p.Subcommand())
+		assert.Equal(t, []string{"grandparent", "parent", "child"}, p.SubcommandNames())
+	}
+
+	{
+		var args root
+		p, err := pparse("grandparent parent", &args)
+		require.NoError(t, err)
+		require.NotNil(t, args.Grandparent)
+		require.NotNil(t, args.Grandparent.Parent)
+		require.Nil(t, args.Grandparent.Parent.Child)
+		assert.Equal(t, args.Grandparent.Parent, p.Subcommand())
+		assert.Equal(t, []string{"grandparent", "parent"}, p.SubcommandNames())
+	}
+
+	{
+		var args root
+		p, err := pparse("grandparent", &args)
+		require.NoError(t, err)
+		require.NotNil(t, args.Grandparent)
+		require.Nil(t, args.Grandparent.Parent)
+		assert.Equal(t, args.Grandparent, p.Subcommand())
+		assert.Equal(t, []string{"grandparent"}, p.SubcommandNames())
+	}
+
+	{
+		var args root
+		p, err := pparse("", &args)
+		require.NoError(t, err)
+		require.Nil(t, args.Grandparent)
+		assert.Nil(t, p.Subcommand())
+		assert.Empty(t, p.SubcommandNames())
+	}
+}
+
+func TestSubcommandsWithPositionals(t *testing.T) {
+	type listCmd struct {
+		Pattern string `arg:"positional"`
+	}
+	type cmd struct {
+		Format string
+		List   *listCmd `arg:"subcommand"`
+	}
+
+	{
+		var args cmd
+		err := parse("list", &args)
+		require.NoError(t, err)
+		assert.NotNil(t, args.List)
+		assert.Equal(t, "", args.List.Pattern)
+	}
+
+	{
+		var args cmd
+		err := parse("list --format json", &args)
+		require.NoError(t, err)
+		assert.NotNil(t, args.List)
+		assert.Equal(t, "", args.List.Pattern)
+		assert.Equal(t, "json", args.Format)
+	}
+
+	{
+		var args cmd
+		err := parse("list somepattern", &args)
+		require.NoError(t, err)
+		assert.NotNil(t, args.List)
+		assert.Equal(t, "somepattern", args.List.Pattern)
+	}
+
+	{
+		var args cmd
+		err := parse("list somepattern --format json", &args)
+		require.NoError(t, err)
+		assert.NotNil(t, args.List)
+		assert.Equal(t, "somepattern", args.List.Pattern)
+		assert.Equal(t, "json", args.Format)
+	}
+
+	{
+		var args cmd
+		err := parse("list --format json somepattern", &args)
+		require.NoError(t, err)
+		assert.NotNil(t, args.List)
+		assert.Equal(t, "somepattern", args.List.Pattern)
+		assert.Equal(t, "json", args.Format)
+	}
+
+	{
+		var args cmd
+		err := parse("--format json list somepattern", &args)
+		require.NoError(t, err)
+		assert.NotNil(t, args.List)
+		assert.Equal(t, "somepattern", args.List.Pattern)
+		assert.Equal(t, "json", args.Format)
+	}
+
+	{
+		var args cmd
+		err := parse("--format json", &args)
+		require.NoError(t, err)
+		assert.Nil(t, args.List)
+		assert.Equal(t, "json", args.Format)
+	}
+}
+func TestSubcommandsWithMultiplePositionals(t *testing.T) {
+	type getCmd struct {
+		Items []string `arg:"positional"`
+	}
+	type cmd struct {
+		Limit int
+		Get   *getCmd `arg:"subcommand"`
+	}
+
+	{
+		var args cmd
+		err := parse("get", &args)
+		require.NoError(t, err)
+		assert.NotNil(t, args.Get)
+		assert.Empty(t, args.Get.Items)
+	}
+
+	{
+		var args cmd
+		err := parse("get --limit 5", &args)
+		require.NoError(t, err)
+		assert.NotNil(t, args.Get)
+		assert.Empty(t, args.Get.Items)
+		assert.Equal(t, 5, args.Limit)
+	}
+
+	{
+		var args cmd
+		err := parse("get item1", &args)
+		require.NoError(t, err)
+		assert.NotNil(t, args.Get)
+		assert.Equal(t, []string{"item1"}, args.Get.Items)
+	}
+
+	{
+		var args cmd
+		err := parse("get item1 item2 item3", &args)
+		require.NoError(t, err)
+		assert.NotNil(t, args.Get)
+		assert.Equal(t, []string{"item1", "item2", "item3"}, args.Get.Items)
+	}
+
+	{
+		var args cmd
+		err := parse("get item1 --limit 5 item2", &args)
+		require.NoError(t, err)
+		assert.NotNil(t, args.Get)
+		assert.Equal(t, []string{"item1", "item2"}, args.Get.Items)
+		assert.Equal(t, 5, args.Limit)
+	}
+}
+
+func TestValForNilStruct(t *testing.T) {
+	type subcmd struct{}
+	var cmd struct {
+		Sub *subcmd `arg:"subcommand"`
+	}
+
+	_, err := NewParser(Config{}, &cmd)
+	require.NoError(t, err)
+
+	require.Nil(t, cmd.Sub)
+}

vendor/github.com/alexflint/go-arg/usage.go

@@ -3,20 +3,12 @@ package arg
 import (
 	"fmt"
 	"io"
-	"os"
 	"strings"
 )
 
 // the width of the left column
 const colWidth = 25
 
-// to allow monkey patching in tests
-var (
-	stdout io.Writer = os.Stdout
-	stderr io.Writer = os.Stderr
-	osExit           = os.Exit
-)
-
 // Fail prints usage information to stderr and exits with non-zero status
 func (p *Parser) Fail(msg string) {
 	p.failWithSubcommand(msg, p.cmd)
@@ -39,9 +31,9 @@ func (p *Parser) FailSubcommand(msg string, subcommand ...string) error {
 
 // failWithSubcommand prints usage information for the given subcommand to stderr and exits with non-zero status
 func (p *Parser) failWithSubcommand(msg string, cmd *command) {
-	p.writeUsageForSubcommand(stderr, cmd)
-	fmt.Fprintln(stderr, "error:", msg)
-	osExit(-1)
+	p.writeUsageForSubcommand(p.config.Out, cmd)
+	fmt.Fprintln(p.config.Out, "error:", msg)
+	p.config.Exit(-1)
 }
 
 // WriteUsage writes usage information to the given writer
@@ -70,7 +62,7 @@ func (p *Parser) WriteUsageForSubcommand(w io.Writer, subcommand ...string) erro
 // writeUsageForSubcommand writes usage information for the given subcommand
 func (p *Parser) writeUsageForSubcommand(w io.Writer, cmd *command) {
 	var positionals, longOptions, shortOptions []*spec
-	for _, spec := range cmd.specs {
+	for _, spec := range cmd.specs() {
 		switch {
 		case spec.positional:
 			positionals = append(positionals, spec)
@@ -216,24 +208,18 @@ func (p *Parser) WriteHelpForSubcommand(w io.Writer, subcommand ...string) error
 
 // writeHelp writes the usage string for the given subcommand
 func (p *Parser) writeHelpForSubcommand(w io.Writer, cmd *command) {
-	var positionals, longOptions, shortOptions []*spec
-	for _, spec := range cmd.specs {
-		switch {
-		case spec.positional:
-			positionals = append(positionals, spec)
-		case spec.long != "":
-			longOptions = append(longOptions, spec)
-		case spec.short != "":
-			shortOptions = append(shortOptions, spec)
-		}
-	}
-
 	if p.description != "" {
 		fmt.Fprintln(w, p.description)
 	}
 	p.writeUsageForSubcommand(w, cmd)
 
 	// write the list of positionals
+	var positionals []*spec
+	for _, spec := range cmd.options {
+		if spec.positional {
+			positionals = append(positionals, spec)
+		}
+	}
 	if len(positionals) > 0 {
 		fmt.Fprint(w, "\nPositional arguments:\n")
 		for _, spec := range positionals {
@@ -242,26 +228,18 @@ func (p *Parser) writeHelpForSubcommand(w io.Writer, cmd *command) {
 	}
 
 	// write the list of options with the short-only ones first to match the usage string
-	if len(shortOptions)+len(longOptions) > 0 || cmd.parent == nil {
-		fmt.Fprint(w, "\nOptions:\n")
-		for _, spec := range shortOptions {
-			p.printOption(w, spec)
-		}
-		for _, spec := range longOptions {
-			p.printOption(w, spec)
-		}
-	}
+	p.writeHelpForArguments(w, cmd, "Options", "")
 
 	// obtain a flattened list of options from all ancestors
 	var globals []*spec
 	ancestor := cmd.parent
 	for ancestor != nil {
-		globals = append(globals, ancestor.specs...)
+		globals = append(globals, ancestor.specs()...)
 		ancestor = ancestor.parent
 	}
 
 	// write the list of global options
-	if len(globals) > 0 {
+	if len(globals) > 0 || len(cmd.groups) > 0 {
 		fmt.Fprint(w, "\nGlobal options:\n")
 		for _, spec := range globals {
 			p.printOption(w, spec)
@@ -290,6 +268,54 @@ func (p *Parser) writeHelpForSubcommand(w io.Writer, cmd *command) {
 			printTwoCols(w, subcmd.name, subcmd.help, "", "")
 		}
 	}
+
+	if p.epilogue != "" {
+		fmt.Fprintln(w, "\n"+p.epilogue)
+	}
+}
+
+// writeHelpForArguments writes the list of short, long, and environment-only
+// options in order.
+func (p *Parser) writeHelpForArguments(w io.Writer, cmd *command, header, help string) {
+	var positionals, longOptions, shortOptions, envOnly []*spec
+	for _, spec := range cmd.options {
+		switch {
+		case spec.positional:
+			positionals = append(positionals, spec)
+		case spec.long != "":
+			longOptions = append(longOptions, spec)
+		case spec.short != "":
+			shortOptions = append(shortOptions, spec)
+		case spec.env != "":
+			envOnly = append(envOnly, spec)
+		}
+	}
+
+	if cmd.parent != nil && len(shortOptions)+len(longOptions)+len(envOnly) == 0 {
+		return
+	}
+
+	// write the list of options with the short-only ones first to match the usage string
+	fmt.Fprintf(w, "\n%v:\n", header)
+	if help != "" {
+		fmt.Fprintf(w, "\n%v\n\n", help)
+	}
+	for _, spec := range shortOptions {
+		p.printOption(w, spec)
+	}
+	for _, spec := range longOptions {
+		p.printOption(w, spec)
+	}
+	for _, spec := range envOnly {
+		p.printOption(w, spec)
+	}
+
+	// write the list of argument groups
+	if len(cmd.groups) > 0 {
+		for _, grpCmd := range cmd.groups {
+			p.writeHelpForArguments(w, grpCmd, fmt.Sprintf("%s options", grpCmd.name), grpCmd.help)
+		}
+	}
 }
 
 func (p *Parser) printOption(w io.Writer, spec *spec) {
@@ -300,8 +326,11 @@ func (p *Parser) printOption(w io.Writer, spec *spec) {
 	if spec.short != "" {
 		ways = append(ways, synopsis(spec, "-"+spec.short))
 	}
+	if spec.env != "" && len(ways) == 0 {
+		ways = append(ways, "(environment only)")
+	}
 	if len(ways) > 0 {
-		printTwoCols(w, strings.Join(ways, ", "), spec.help, spec.defaultVal, spec.env)
+		printTwoCols(w, strings.Join(ways, ", "), spec.help, spec.defaultString, spec.env)
 	}
 }
 

vendor/github.com/alexflint/go-arg/usage_test.go

@@ -0,0 +1,846 @@
+package arg
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"os"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+type NameDotName struct {
+	Head, Tail string
+}
+
+func (n *NameDotName) UnmarshalText(b []byte) error {
+	s := string(b)
+	pos := strings.Index(s, ".")
+	if pos == -1 {
+		return fmt.Errorf("missing period in %s", s)
+	}
+	n.Head = s[:pos]
+	n.Tail = s[pos+1:]
+	return nil
+}
+
+func (n *NameDotName) MarshalText() (text []byte, err error) {
+	text = []byte(fmt.Sprintf("%s.%s", n.Head, n.Tail))
+	return
+}
+
+func TestWriteUsage(t *testing.T) {
+	expectedUsage := "Usage: example [--name NAME] [--value VALUE] [--verbose] [--dataset DATASET] [--optimize OPTIMIZE] [--ids IDS] [--values VALUES] [--workers WORKERS] [--testenv TESTENV] [--file FILE] INPUT [OUTPUT [OUTPUT ...]]"
+
+	expectedHelp := `
+Usage: example [--name NAME] [--value VALUE] [--verbose] [--dataset DATASET] [--optimize OPTIMIZE] [--ids IDS] [--values VALUES] [--workers WORKERS] [--testenv TESTENV] [--file FILE] INPUT [OUTPUT [OUTPUT ...]]
+
+Positional arguments:
+  INPUT
+  OUTPUT                 list of outputs
+
+Options:
+  --name NAME            name to use [default: Foo Bar]
+  --value VALUE          secret value [default: 42]
+  --verbose, -v          verbosity level
+  --dataset DATASET      dataset to use
+  --optimize OPTIMIZE, -O OPTIMIZE
+                         optimization level
+  --ids IDS              Ids
+  --values VALUES        Values [default: [3.14 42 256]]
+  --workers WORKERS, -w WORKERS
+                         number of workers to start [default: 10, env: WORKERS]
+  --testenv TESTENV, -a TESTENV [env: TEST_ENV]
+  --file FILE, -f FILE   File with mandatory extension [default: scratch.txt]
+  --help, -h             display this help and exit
+`
+
+	var args struct {
+		Input    string       `arg:"positional,required"`
+		Output   []string     `arg:"positional" help:"list of outputs"`
+		Name     string       `help:"name to use"`
+		Value    int          `help:"secret value"`
+		Verbose  bool         `arg:"-v" help:"verbosity level"`
+		Dataset  string       `help:"dataset to use"`
+		Optimize int          `arg:"-O" help:"optimization level"`
+		Ids      []int64      `help:"Ids"`
+		Values   []float64    `help:"Values"`
+		Workers  int          `arg:"-w,env:WORKERS" help:"number of workers to start" default:"10"`
+		TestEnv  string       `arg:"-a,env:TEST_ENV"`
+		File     *NameDotName `arg:"-f" help:"File with mandatory extension"`
+	}
+	args.Name = "Foo Bar"
+	args.Value = 42
+	args.Values = []float64{3.14, 42, 256}
+	args.File = &NameDotName{"scratch", "txt"}
+	p, err := NewParser(Config{Program: "example"}, &args)
+	require.NoError(t, err)
+
+	os.Args[0] = "example"
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+}
+
+type MyEnum int
+
+func (n *MyEnum) UnmarshalText(b []byte) error {
+	return nil
+}
+
+func (n *MyEnum) MarshalText() ([]byte, error) {
+	return nil, errors.New("There was a problem")
+}
+
+func TestUsageWithDefaults(t *testing.T) {
+	expectedUsage := "Usage: example [--label LABEL] [--content CONTENT]"
+
+	expectedHelp := `
+Usage: example [--label LABEL] [--content CONTENT]
+
+Options:
+  --label LABEL [default: cat]
+  --content CONTENT [default: dog]
+  --help, -h             display this help and exit
+`
+	var args struct {
+		Label   string
+		Content string `default:"dog"`
+	}
+	args.Label = "cat"
+	p, err := NewParser(Config{Program: "example"}, &args)
+	require.NoError(t, err)
+
+	args.Label = "should_ignore_this"
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+}
+
+func TestUsageCannotMarshalToString(t *testing.T) {
+	var args struct {
+		Name *MyEnum
+	}
+	v := MyEnum(42)
+	args.Name = &v
+	_, err := NewParser(Config{Program: "example"}, &args)
+	assert.EqualError(t, err, `args.Name: error marshaling default value to string: There was a problem`)
+}
+
+func TestUsageLongPositionalWithHelp_legacyForm(t *testing.T) {
+	expectedUsage := "Usage: example [VERYLONGPOSITIONALWITHHELP]"
+
+	expectedHelp := `
+Usage: example [VERYLONGPOSITIONALWITHHELP]
+
+Positional arguments:
+  VERYLONGPOSITIONALWITHHELP
+                         this positional argument is very long but cannot include commas
+
+Options:
+  --help, -h             display this help and exit
+`
+	var args struct {
+		VeryLongPositionalWithHelp string `arg:"positional,help:this positional argument is very long but cannot include commas"`
+	}
+
+	p, err := NewParser(Config{Program: "example"}, &args)
+	require.NoError(t, err)
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+}
+
+func TestUsageLongPositionalWithHelp_newForm(t *testing.T) {
+	expectedUsage := "Usage: example [VERYLONGPOSITIONALWITHHELP]"
+
+	expectedHelp := `
+Usage: example [VERYLONGPOSITIONALWITHHELP]
+
+Positional arguments:
+  VERYLONGPOSITIONALWITHHELP
+                         this positional argument is very long, and includes: commas, colons etc
+
+Options:
+  --help, -h             display this help and exit
+`
+	var args struct {
+		VeryLongPositionalWithHelp string `arg:"positional" help:"this positional argument is very long, and includes: commas, colons etc"`
+	}
+
+	p, err := NewParser(Config{Program: "example"}, &args)
+	require.NoError(t, err)
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+}
+
+func TestUsageWithProgramName(t *testing.T) {
+	expectedUsage := "Usage: myprogram"
+
+	expectedHelp := `
+Usage: myprogram
+
+Options:
+  --help, -h             display this help and exit
+`
+	config := Config{
+		Program: "myprogram",
+	}
+	p, err := NewParser(config, &struct{}{})
+	require.NoError(t, err)
+
+	os.Args[0] = "example"
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+}
+
+type versioned struct{}
+
+// Version returns the version for this program
+func (versioned) Version() string {
+	return "example 3.2.1"
+}
+
+func TestUsageWithVersion(t *testing.T) {
+	expectedUsage := "example 3.2.1\nUsage: example"
+
+	expectedHelp := `
+example 3.2.1
+Usage: example
+
+Options:
+  --help, -h             display this help and exit
+  --version              display version and exit
+`
+	os.Args[0] = "example"
+	p, err := NewParser(Config{}, &versioned{})
+	require.NoError(t, err)
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+}
+
+type described struct{}
+
+// Described returns the description for this program
+func (described) Description() string {
+	return "this program does this and that"
+}
+
+func TestUsageWithDescription(t *testing.T) {
+	expectedUsage := "Usage: example"
+
+	expectedHelp := `
+this program does this and that
+Usage: example
+
+Options:
+  --help, -h             display this help and exit
+`
+	os.Args[0] = "example"
+	p, err := NewParser(Config{}, &described{})
+	require.NoError(t, err)
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+}
+
+type epilogued struct{}
+
+// Epilogued returns the epilogue for this program
+func (epilogued) Epilogue() string {
+	return "For more information visit github.com/alexflint/go-arg"
+}
+
+func TestUsageWithEpilogue(t *testing.T) {
+	expectedUsage := "Usage: example"
+
+	expectedHelp := `
+Usage: example
+
+Options:
+  --help, -h             display this help and exit
+
+For more information visit github.com/alexflint/go-arg
+`
+	os.Args[0] = "example"
+	p, err := NewParser(Config{}, &epilogued{})
+	require.NoError(t, err)
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+}
+
+func TestUsageForRequiredPositionals(t *testing.T) {
+	expectedUsage := "Usage: example REQUIRED1 REQUIRED2\n"
+	var args struct {
+		Required1 string `arg:"positional,required"`
+		Required2 string `arg:"positional,required"`
+	}
+
+	p, err := NewParser(Config{Program: "example"}, &args)
+	require.NoError(t, err)
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, usage.String())
+}
+
+func TestUsageForMixedPositionals(t *testing.T) {
+	expectedUsage := "Usage: example REQUIRED1 REQUIRED2 [OPTIONAL1 [OPTIONAL2]]\n"
+	var args struct {
+		Required1 string `arg:"positional,required"`
+		Required2 string `arg:"positional,required"`
+		Optional1 string `arg:"positional"`
+		Optional2 string `arg:"positional"`
+	}
+
+	p, err := NewParser(Config{Program: "example"}, &args)
+	require.NoError(t, err)
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, usage.String())
+}
+
+func TestUsageForRepeatedPositionals(t *testing.T) {
+	expectedUsage := "Usage: example REQUIRED1 REQUIRED2 REPEATED [REPEATED ...]\n"
+	var args struct {
+		Required1 string   `arg:"positional,required"`
+		Required2 string   `arg:"positional,required"`
+		Repeated  []string `arg:"positional,required"`
+	}
+
+	p, err := NewParser(Config{Program: "example"}, &args)
+	require.NoError(t, err)
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, usage.String())
+}
+
+func TestUsageForMixedAndRepeatedPositionals(t *testing.T) {
+	expectedUsage := "Usage: example REQUIRED1 REQUIRED2 [OPTIONAL1 [OPTIONAL2 [REPEATED [REPEATED ...]]]]\n"
+	var args struct {
+		Required1 string   `arg:"positional,required"`
+		Required2 string   `arg:"positional,required"`
+		Optional1 string   `arg:"positional"`
+		Optional2 string   `arg:"positional"`
+		Repeated  []string `arg:"positional"`
+	}
+
+	p, err := NewParser(Config{Program: "example"}, &args)
+	require.NoError(t, err)
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, usage.String())
+}
+
+func TestRequiredMultiplePositionals(t *testing.T) {
+	expectedUsage := "Usage: example REQUIREDMULTIPLE [REQUIREDMULTIPLE ...]\n"
+
+	expectedHelp := `
+Usage: example REQUIREDMULTIPLE [REQUIREDMULTIPLE ...]
+
+Positional arguments:
+  REQUIREDMULTIPLE       required multiple positional
+
+Options:
+  --help, -h             display this help and exit
+`
+	var args struct {
+		RequiredMultiple []string `arg:"positional,required" help:"required multiple positional"`
+	}
+
+	p, err := NewParser(Config{Program: "example"}, &args)
+	require.NoError(t, err)
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, usage.String())
+}
+
+func TestUsageWithNestedSubcommands(t *testing.T) {
+	expectedUsage := "Usage: example child nested [--enable] OUTPUT"
+
+	expectedHelp := `
+Usage: example child nested [--enable] OUTPUT
+
+Positional arguments:
+  OUTPUT
+
+Options:
+  --enable
+
+Global options:
+  --values VALUES        Values
+  --verbose, -v          verbosity level
+  --help, -h             display this help and exit
+`
+
+	var args struct {
+		Verbose bool `arg:"-v" help:"verbosity level"`
+		Child   *struct {
+			Values []float64 `help:"Values"`
+			Nested *struct {
+				Enable bool
+				Output string `arg:"positional,required"`
+			} `arg:"subcommand:nested"`
+		} `arg:"subcommand:child"`
+	}
+
+	os.Args[0] = "example"
+	p, err := NewParser(Config{}, &args)
+	require.NoError(t, err)
+
+	_ = p.Parse([]string{"child", "nested", "value"})
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var help2 bytes.Buffer
+	p.WriteHelpForSubcommand(&help2, "child", "nested")
+	assert.Equal(t, expectedHelp[1:], help2.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+
+	var usage2 bytes.Buffer
+	p.WriteUsageForSubcommand(&usage2, "child", "nested")
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage2.String()))
+}
+
+func TestNonexistentSubcommand(t *testing.T) {
+	var args struct {
+		sub *struct{} `arg:"subcommand"`
+	}
+	p, err := NewParser(Config{}, &args)
+	require.NoError(t, err)
+
+	var b bytes.Buffer
+
+	err = p.WriteUsageForSubcommand(&b, "does_not_exist")
+	assert.Error(t, err)
+
+	err = p.WriteHelpForSubcommand(&b, "does_not_exist")
+	assert.Error(t, err)
+
+	err = p.FailSubcommand("something went wrong", "does_not_exist")
+	assert.Error(t, err)
+
+	err = p.WriteUsageForSubcommand(&b, "sub", "does_not_exist")
+	assert.Error(t, err)
+
+	err = p.WriteHelpForSubcommand(&b, "sub", "does_not_exist")
+	assert.Error(t, err)
+
+	err = p.FailSubcommand("something went wrong", "sub", "does_not_exist")
+	assert.Error(t, err)
+}
+
+func TestUsageWithOptionGroup(t *testing.T) {
+	expectedUsage := "Usage: example [--verbose] [--insecure] [--host HOST] [--port PORT] [--user USER] OUTPUT"
+
+	expectedHelp := `
+Usage: example [--verbose] [--insecure] [--host HOST] [--port PORT] [--user USER] OUTPUT
+
+Positional arguments:
+  OUTPUT
+
+Options:
+  --verbose, -v          verbosity level
+
+Database options:
+
+This block represents related arguments.
+
+  --insecure, -i         disable tls
+  --host HOST            hostname to connect to [default: localhost, env: DB_HOST]
+  --port PORT            port to connect to [default: 3306, env: DB_PORT]
+  --user USER            username to connect as [env: DB_USERNAME]
+  (environment only)     password to connect with [env: DB_PASSWORD]
+
+Global options:
+  --help, -h             display this help and exit
+`
+
+	type database struct {
+		Insecure bool   `arg:"-i,--insecure" help:"disable tls"`
+		Host     string `arg:"--host,env:DB_HOST" help:"hostname to connect to" default:"localhost"`
+		Port     string `arg:"--port,env:DB_PORT" help:"port to connect to" default:"3306"`
+		User     string `arg:"--user,env:DB_USERNAME" help:"username to connect as"`
+		Password string `arg:"--,env:DB_PASSWORD" help:"password to connect with"`
+	}
+
+	var args struct {
+		Verbose  bool      `arg:"-v" help:"verbosity level"`
+		Database *database `arg:"group" help:"This block represents related arguments."`
+		Output   string    `arg:"positional,required"`
+	}
+
+	os.Args[0] = "example"
+	p, err := NewParser(Config{}, &args)
+	require.NoError(t, err)
+
+	_ = p.Parse([]string{})
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+}
+
+func TestUsageWithoutSubcommandAndOptionGroup(t *testing.T) {
+	expectedUsage := "Usage: example [-s] [--global] <command> [<args>]"
+
+	expectedHelp := `
+Usage: example [-s] [--global] <command> [<args>]
+
+Options:
+  --global, -g           global option
+
+Global group options:
+
+This block represents related arguments.
+
+  -s                     global something
+
+Global options:
+  --help, -h             display this help and exit
+
+Commands:
+  foo                    Command A
+  bar                    Command B
+`
+
+	var args struct {
+		Global      bool `arg:"-g" help:"global option"`
+		GlobalGroup *struct {
+			Something bool `arg:"-s,--" help:"global something"`
+		} `arg:"group:Global group" help:"This block represents related arguments."`
+		CommandA *struct {
+			OptionA bool `arg:"-a,--" help:"option for sub A"`
+			GroupA  *struct {
+				GroupA bool `arg:"--group-a" help:"group belonging to cmd A"`
+			} `arg:"group:Group A" help:"This block belongs to command A."`
+		} `arg:"subcommand:foo" help:"Command A"`
+		CommandB *struct {
+			OptionB bool `arg:"-b,--" help:"option for sub B"`
+			GroupB  *struct {
+				GroupB      bool `arg:"--group-b" help:"group belonging to cmd B"`
+				NestedGroup *struct {
+					NestedGroup bool `arg:"--nested-group" help:"nested group belonging to group B of cmd B"`
+				} `arg:"group:Nested Group" help:"This block belongs to group B of command B."`
+			} `arg:"group:Group B" help:"This block belongs to command B."`
+		} `arg:"subcommand:bar" help:"Command B"`
+	}
+
+	os.Args[0] = "example"
+	p, err := NewParser(Config{}, &args)
+	require.NoError(t, err)
+
+	_ = p.Parse([]string{})
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var help2 bytes.Buffer
+	p.WriteHelpForSubcommand(&help2)
+	assert.Equal(t, expectedHelp[1:], help2.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+
+	var usage2 bytes.Buffer
+	p.WriteUsageForSubcommand(&usage2)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage2.String()))
+}
+
+func TestUsageWithSubcommandAndOptionGroup(t *testing.T) {
+
+	expectedUsage := "Usage: example bar [-b] [--group-b] [--nested-group]"
+	expectedHelp := `
+Usage: example bar [-b] [--group-b] [--nested-group]
+
+Options:
+  -b                     option for sub B
+
+Group B options:
+
+This block belongs to command B.
+
+  --group-b              group belonging to cmd B
+
+Nested Group options:
+
+This block belongs to group B of command B.
+
+  --nested-group         nested group belonging to group B of cmd B
+
+Global options:
+  --global, -g           global option
+  -s                     global something
+  --help, -h             display this help and exit
+`
+
+	var args struct {
+		Global      bool `arg:"-g" help:"global option"`
+		GlobalGroup *struct {
+			Something bool `arg:"-s,--" help:"global something"`
+		} `arg:"group:Global group" help:"This block represents related arguments."`
+		CommandA *struct {
+			OptionA bool `arg:"-a,--" help:"option for sub A"`
+			GroupA  *struct {
+				GroupA bool `arg:"--group-a" help:"group belonging to cmd A"`
+			} `arg:"group:Group A" help:"This block belongs to command A."`
+		} `arg:"subcommand:foo" help:"Command A"`
+		CommandB *struct {
+			OptionB bool `arg:"-b,--" help:"option for sub B"`
+			GroupB  *struct {
+				GroupB      bool `arg:"--group-b" help:"group belonging to cmd B"`
+				NestedGroup *struct {
+					NestedGroup bool `arg:"--nested-group" help:"nested group belonging to group B of cmd B"`
+				} `arg:"group:Nested Group" help:"This block belongs to group B of command B."`
+			} `arg:"group:Group B" help:"This block belongs to command B."`
+		} `arg:"subcommand:bar" help:"Command B"`
+	}
+
+	os.Args[0] = "example"
+	p, err := NewParser(Config{}, &args)
+	require.NoError(t, err)
+
+	_ = p.Parse([]string{"bar"})
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var help2 bytes.Buffer
+	p.WriteHelpForSubcommand(&help2, "bar")
+	assert.Equal(t, expectedHelp[1:], help2.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+
+	var usage2 bytes.Buffer
+	p.WriteUsageForSubcommand(&usage2, "bar")
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage2.String()))
+}
+
+func TestUsageWithoutLongNames(t *testing.T) {
+	expectedUsage := "Usage: example [-a PLACEHOLDER] -b SHORTONLY2"
+
+	expectedHelp := `
+Usage: example [-a PLACEHOLDER] -b SHORTONLY2
+
+Options:
+  -a PLACEHOLDER         some help [default: some val]
+  -b SHORTONLY2          some help2
+  --help, -h             display this help and exit
+`
+	var args struct {
+		ShortOnly  string `arg:"-a,--" help:"some help" default:"some val" placeholder:"PLACEHOLDER"`
+		ShortOnly2 string `arg:"-b,--,required" help:"some help2"`
+	}
+	p, err := NewParser(Config{Program: "example"}, &args)
+	assert.NoError(t, err)
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+}
+
+func TestUsageWithShortFirst(t *testing.T) {
+	expectedUsage := "Usage: example [-c CAT] [--dog DOG]"
+
+	expectedHelp := `
+Usage: example [-c CAT] [--dog DOG]
+
+Options:
+  -c CAT
+  --dog DOG
+  --help, -h             display this help and exit
+`
+	var args struct {
+		Dog string
+		Cat string `arg:"-c,--"`
+	}
+	p, err := NewParser(Config{Program: "example"}, &args)
+	assert.NoError(t, err)
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+}
+
+func TestUsageWithEnvOptions(t *testing.T) {
+	expectedUsage := "Usage: example [-s SHORT]"
+
+	expectedHelp := `
+Usage: example [-s SHORT]
+
+Options:
+  -s SHORT [env: SHORT]
+  (environment only) [env: ENVONLY]
+  (environment only) [env: CUSTOM]
+  --help, -h             display this help and exit
+`
+	var args struct {
+		Short            string `arg:"--,-s,env"`
+		EnvOnly          string `arg:"--,env"`
+		EnvOnlyOverriden string `arg:"--,env:CUSTOM"`
+	}
+
+	p, err := NewParser(Config{Program: "example"}, &args)
+	assert.NoError(t, err)
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+
+	var usage bytes.Buffer
+	p.WriteUsage(&usage)
+	assert.Equal(t, expectedUsage, strings.TrimSpace(usage.String()))
+}
+
+func TestFail(t *testing.T) {
+	var stdout bytes.Buffer
+	var exitCode int
+	exit := func(code int) { exitCode = code }
+
+	expectedStdout := `
+Usage: example [--foo FOO]
+error: something went wrong
+`
+
+	var args struct {
+		Foo int
+	}
+	p, err := NewParser(Config{Program: "example", Exit: exit, Out: &stdout}, &args)
+	require.NoError(t, err)
+	p.Fail("something went wrong")
+
+	assert.Equal(t, expectedStdout[1:], stdout.String())
+	assert.Equal(t, -1, exitCode)
+}
+
+func TestFailSubcommand(t *testing.T) {
+	var stdout bytes.Buffer
+	var exitCode int
+	exit := func(code int) { exitCode = code }
+
+	expectedStdout := `
+Usage: example sub
+error: something went wrong
+`
+
+	var args struct {
+		Sub *struct{} `arg:"subcommand"`
+	}
+	p, err := NewParser(Config{Program: "example", Exit: exit, Out: &stdout}, &args)
+	require.NoError(t, err)
+
+	err = p.FailSubcommand("something went wrong", "sub")
+	require.NoError(t, err)
+
+	assert.Equal(t, expectedStdout[1:], stdout.String())
+	assert.Equal(t, -1, exitCode)
+}
+
+type lengthOf struct {
+	Length int
+}
+
+func (p *lengthOf) UnmarshalText(b []byte) error {
+	p.Length = len(b)
+	return nil
+}
+
+func TestHelpShowsDefaultValueFromOriginalTag(t *testing.T) {
+	// check that the usage text prints the original string from the default tag, not
+	// the serialization of the parsed value
+
+	expectedHelp := `
+Usage: example [--test TEST]
+
+Options:
+  --test TEST [default: some_default_value]
+  --help, -h             display this help and exit
+`
+
+	var args struct {
+		Test *lengthOf `default:"some_default_value"`
+	}
+	p, err := NewParser(Config{Program: "example"}, &args)
+	require.NoError(t, err)
+
+	var help bytes.Buffer
+	p.WriteHelp(&help)
+	assert.Equal(t, expectedHelp[1:], help.String())
+}