add env var defaults

cli_test.go

@@ -180,13 +180,32 @@ func Test_git(t *testing.T) {
 				}
 			},
 		},
+		"env var based flag is evaluated": {
+			gitHandler: func(t *testing.T) Handler {
+				called := ensureCalled(t)
+
+				return func(ctx context.Context) error {
+					called()
+
+					globalGitignore, err := FlagValue[string](ctx, "global-gitignore")
+					test.Nil(t, err)
+					test.Equal(t, globalGitignore, "path/to/some/.gitignore")
+					return nil
+				}
+			},
+		},
 	}
 
 	for name, testCase := range testCases {
 		t.Run(name, func(t *testing.T) {
+			t.Setenv("GLOBAL_GITIGNORE", "path/to/some/.gitignore")
+
 			command, err := NewCommand("git", "the stupid content tracker",
 				SetVersion("v0.1.0"),
 				AddFlag("git-dir", "Git directory to use"),
+				AddFlag("global-gitignore", "Global .gitignore file to use.",
+					SetFlagDefaultEnv("GLOBAL_GITIGNORE"),
+				),
 				AddSubCmd("commit", "Record changes to the repository",
 					AddFlag("message", "commit message",
 						AddFlagAlias("msg"),

command_test.go

@@ -8,8 +8,9 @@ func ExampleNewCommand() {
 		AddVersionFlag(AddFlagShort('V')),
 		AddHelpFlag(AddFlagShort('h')),
 		AddFlag("port", "Port to run server on.",
-			SetFlagDefault(3000),
 			AddFlagShort('p'),
+			SetFlagDefault(3000),
+			SetFlagDefaultEnv("PORT"),
 		),
 		AddFlag("auth-required", "Whether to require authentication.",
 			SetFlagDefault(true),
@@ -26,14 +27,14 @@ func ExampleNewCommand() {
 	// server v0.1.0: An http server.
 	//
 	// Usage:
-	//   server [flags] [sub-commands]
+	//   server [flags] [sub-command]
 	//
-	// Sub-commands:
+	// Sub-command:
 	//   proxy: Proxy requests to another server.
 	//
 	// Flags:
 	//   --version        -V  Print version.                      (type: bool, default: "false")
 	//   --help           -h  Print help.                         (type: bool, default: "false")
-	//   --port           -p  Port to run server on.              (type: int, default: "3000")
+	//   --port           -p  Port to run server on.              (type: int, default: $PORT, "3000")
 	//   --auth-required      Whether to require authentication.  (type: bool, default: "true")
 }

context.go

@@ -2,6 +2,7 @@ package cli
 
 import (
 	"context"
+	"os"
 
 	"github.com/bobg/errors"
 )
@@ -29,6 +30,15 @@ func FlagValue[T any](ctx context.Context, name string) (T, error) {
 		return flag.value.(T), nil
 	}
 
+	if flag.defaultEnvName != "" {
+		value, err := flag.parser.Parse(os.Getenv(flag.defaultEnvName))
+		if err != nil {
+			return zero, err
+		}
+
+		return value.(T), nil
+	}
+
 	return flag.defaultValue.(T), nil
 }
 

flag.go

@@ -11,16 +11,17 @@ import (
 const helpFlagName = "help"
 
 type Flag struct {
-	name         string
-	description  string
-	aliases      []string
-	shorts       []rune
-	isHelp       bool
-	isVersion    bool
-	isHidden     bool
-	isInherited  bool
-	parser       argParser
-	defaultValue any
+	name           string
+	description    string
+	aliases        []string
+	shorts         []rune
+	isHelp         bool
+	isVersion      bool
+	isHidden       bool
+	isInherited    bool
+	parser         argParser
+	defaultEnvName string
+	defaultValue   any
 
 	value any
 }

flag_options.go

@@ -59,6 +59,14 @@ func SetFlagDefaultAndParser[T any](defaultValue T, argParser ArgParser[T]) opti
 	}
 }
 
+// SetFlagDefaultEnv sets the default value to that of the corresponding environment variable, and parser of the flag.
+func SetFlagDefaultEnv(name string) option.Func[*Flag] {
+	return func(flag *Flag) (*Flag, error) {
+		flag.defaultEnvName = name
+		return flag, nil
+	}
+}
+
 func setFlagIsHelp(isHelp bool) option.Func[*Flag] {
 	return func(flag *Flag) (*Flag, error) {
 		flag.isHelp = isHelp

go.mod

@@ -6,7 +6,7 @@ require (
 	github.com/MakeNowJust/heredoc/v2 v2.0.1
 	github.com/bobg/errors v1.1.0
 	github.com/broothie/option v0.1.0
-	github.com/broothie/test v0.1.6
+	github.com/broothie/test v0.1.8
 	github.com/samber/lo v1.49.1
 )
 

go.sum

@@ -4,8 +4,8 @@ github.com/bobg/errors v1.1.0 h1:gsVanPzJMpZQpwY+27/GQYElZez5CuMYwiIpk2A3RGw=
 github.com/bobg/errors v1.1.0/go.mod h1:Q4775qBZpnte7EGFJqmvnlB1U4pkI1XmU3qxqdp7Zcc=
 github.com/broothie/option v0.1.0 h1:5l6qdv9g1Ajxn7821brKVzOZxIjlVB0gA1MU8QbW8Fw=
 github.com/broothie/option v0.1.0/go.mod h1:doEn1r1TpaaBJRdHLZlsdjvnrnH0u1WW+FZA018hE2g=
-github.com/broothie/test v0.1.6 h1:lvGSA1O2lFdYJuKDgj9IDpX9AA+rQtY/eYGMvui3PyM=
-github.com/broothie/test v0.1.6/go.mod h1:txzDcP9OHro3y7goC+ZznIkASy8NJks4dUcdbwsP0HM=
+github.com/broothie/test v0.1.8 h1:II6ZE0z2ZV0y4GJlLl/oBinG6X58mwyioSd/jxNMea0=
+github.com/broothie/test v0.1.8/go.mod h1:txzDcP9OHro3y7goC+ZznIkASy8NJks4dUcdbwsP0HM=
 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/kylelemons/godebug v1.1.0 h1:RPNrshWIDI6G2gRW9EHilWtl7Z6Sb1BR0xunSBf0SNc=

help.go

@@ -104,12 +104,17 @@ func (h helpContext) FlagTable() (string, error) {
 			shorts = fmt.Sprintf("-%s", string(flag.shorts))
 		}
 
+		helpValues := []string{fmt.Sprintf("%q", fmt.Sprint(flag.defaultValue))}
+		if flag.defaultEnvName != "" {
+			helpValues = append([]string{fmt.Sprintf("$%s", flag.defaultEnvName)}, helpValues...)
+		}
+
 		return []string{
 			"",
 			strings.Join(longs, " "),
 			shorts,
 			flag.description,
-			fmt.Sprintf("(type: %T, default: %q)", flag.parser.Type(), fmt.Sprint(flag.defaultValue)),
+			fmt.Sprintf("(type: %T, default: %s)", flag.parser.Type(), strings.Join(helpValues, ", ")),
 		}, true
 	}))
 }

help.tmpl

@@ -1,10 +1,10 @@
 {{.RootName}}{{ if .Version }} {{.Version}}{{ end }}: {{.RootDescription}}
 
 Usage:
-  {{.QualifiedName}} {{- if .Flags }} [flags]{{ end -}} {{- if .SubCommands }} [sub-commands]{{ end }}{{ if .ArgumentList }} {{.ArgumentList}}{{ end }}
+  {{.QualifiedName}} {{- if .Flags }} [flags]{{ end -}} {{- if .SubCommands }} [sub-command]{{ end }}{{ if .ArgumentList }} {{.ArgumentList}}{{ end }}
 
 {{ if .SubCommands -}}
-Sub-commands:
+Sub-command:
 {{.SubCommandsTable}}
 {{ end -}}
 

help_test.go

@@ -84,9 +84,9 @@ func TestCommand_renderHelp(t *testing.T) {
 				test v1.2.3-rc10: test command
 
 				Usage:
-				  test [flags] [sub-commands]
+				  test [flags] [sub-command]
 
-				Sub-commands:
+				Sub-command:
 				  some-command: some command
 
 				Flags:

options_test.go

@@ -19,6 +19,7 @@ func Test_options(t *testing.T) {
 				AddFlagAlias("addr"),
 				AddFlagShort('p'),
 				SetFlagDefault(3000),
+				SetFlagDefaultEnv("PORT"),
 			),
 			AddSubCmd("proxy", "Proxy requests",
 				AddAlias("p"),
@@ -59,6 +60,7 @@ func Test_options(t *testing.T) {
 		test.DeepEqual(t, []string{"addr"}, portFlag.aliases)
 		test.DeepEqual(t, []rune{'p'}, portFlag.shorts)
 		test.Equal(t, 3000, portFlag.defaultValue)
+		test.Equal(t, "PORT", portFlag.defaultEnvName)
 		test.Nil(t, portFlag.value)
 		test.Equal(t, reflect.ValueOf(IntParser).Pointer(), reflect.ValueOf(portFlag.parser).Pointer())
 		test.False(t, portFlag.isBool())
@@ -126,9 +128,9 @@ func ExampleAddSubCmd() {
 	// server: An http server.
 	//
 	// Usage:
-	//   server [sub-commands]
+	//   server [sub-command]
 	//
-	// Sub-commands:
+	// Sub-command:
 	//   start: Start the server
 }
 
@@ -151,6 +153,29 @@ func ExampleAddFlag() {
 	//   --port  -p  Port to run server on  (type: int, default: "3000")
 }
 
+func ExampleAddFlag_with_env() {
+	os.Setenv("PORT", "8080")
+	defer os.Unsetenv("PORT")
+
+	command, _ := NewCommand("server", "An http server.",
+		AddFlag("port", "Port to run server on",
+			AddFlagShort('p'),
+			SetFlagDefault(3000),
+			SetFlagDefaultEnv("PORT"),
+		),
+	)
+
+	command.renderHelp(os.Stdout)
+	// Output:
+	// server: An http server.
+	//
+	// Usage:
+	//   server [flags]
+	//
+	// Flags:
+	//   --port  -p  Port to run server on  (type: int, default: $PORT, "3000")
+}
+
 func ExampleAddArg() {
 	command, _ := NewCommand("server", "An http server.",
 		AddArg("port", "Port to run server on", SetArgParser(IntParser)),