Merge remote-tracking branch 'origin/master' into default-value-issue

.github/workflows/go.yml

@@ -15,17 +15,17 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        go: ['1.13', '1.14', '1.15', '1.16']
+        go: ['1.17', '1.18', '1.19']
 
     steps:
     - id: go
       name: Set up Go
-      uses: actions/setup-go@v1
+      uses: actions/setup-go@v3
       with:
         go-version: ${{ matrix.go }}
 
     - name: Checkout
-      uses: actions/checkout@v2
+      uses: actions/checkout@v3
 
     - name: Build
       run: go build -v .

README.md

@@ -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*

go.mod

@@ -1,7 +1,7 @@
 module github.com/alexflint/go-arg
 
 require (
-	github.com/alexflint/go-scalar v1.1.0
+	github.com/alexflint/go-scalar v1.2.0
 	github.com/stretchr/testify v1.7.0
 )
 

go.sum

@@ -1,5 +1,7 @@
 github.com/alexflint/go-scalar v1.1.0 h1:aaAouLLzI9TChcPXotr6gUhq+Scr8rl0P9P4PnltbhM=
 github.com/alexflint/go-scalar v1.1.0/go.mod h1:LoFvNMqS1CPrMVltza4LvnGKhaSpc3oyLEBUZVhhS2o=
+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=

parse.go

@@ -83,18 +83,7 @@ func MustParse(dest ...interface{}) *Parser {
 		return nil // just in case osExit was monkey-patched
 	}
 
-	err = p.Parse(flags())
+	p.MustParse(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)
-	}
-
 	return p
 }
 
@@ -122,6 +111,10 @@ 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
 }
 
 // Parser represents a set of command line options with destination values
@@ -131,6 +124,7 @@ type Parser struct {
 	config      Config
 	version     string
 	description string
+	epilogue    string
 
 	// the following field changes during processing of command line arguments
 	lastCmd *command
@@ -152,6 +146,14 @@ 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)
@@ -246,6 +248,9 @@ 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
@@ -470,6 +475,20 @@ 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(stdout, p.lastCmd)
+		osExit(0)
+	case err == ErrVersion:
+		fmt.Fprintln(stdout, p.version)
+		osExit(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 {
@@ -564,7 +583,9 @@ func (p *Parser) process(args []string) error {
 
 			// 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
+			if v.IsNil() {
+				v.Set(reflect.New(v.Type().Elem())) // we already checked that all subcommands are struct pointers
+			}
 
 			// add the new options to the set of allowed options
 			specs = append(specs, subcmd.specs...)
@@ -696,7 +717,13 @@ func (p *Parser) process(args []string) error {
 			}
 			return errors.New(msg)
 		}
-		if spec.defaultValue.IsValid() {
+
+		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)
 		}
 	}

parse_test.go

@@ -96,6 +96,21 @@ func TestInt(t *testing.T) {
 	assert.EqualValues(t, 8, *args.Ptr)
 }
 
+func TestHexOctBin(t *testing.T) {
+	var args struct {
+		Hex int
+		Oct int
+		Bin int
+		Underscored int
+	}
+	err := parse("--hex 0xA --oct 0o10 --bin 0b101 --underscored 123_456", &args)
+	require.NoError(t, err)
+	assert.EqualValues(t, 10, args.Hex)
+	assert.EqualValues(t, 8, args.Oct)
+	assert.EqualValues(t, 5, args.Bin)
+	assert.EqualValues(t, 123456, args.Underscored)
+}
+
 func TestNegativeInt(t *testing.T) {
 	var args struct {
 		Foo int
@@ -817,6 +832,19 @@ func TestEnvironmentVariableIgnored(t *testing.T) {
 	assert.Equal(t, "", args.Foo)
 }
 
+func TestDefaultValuesIgnored(t *testing.T) {
+	var args struct {
+		Foo string `default:"bad"`
+	}
+
+	p, err := NewParser(Config{IgnoreDefault: true}, &args)
+	require.NoError(t, err)
+
+	err = p.Parse(nil)
+	assert.NoError(t, err)
+	assert.Equal(t, "", args.Foo)
+}
+
 func TestEnvironmentVariableInSubcommandIgnored(t *testing.T) {
 	var args struct {
 		Sub *struct {
@@ -833,6 +861,54 @@ func TestEnvironmentVariableInSubcommandIgnored(t *testing.T) {
 	assert.Equal(t, "", args.Sub.Foo)
 }
 
+func TestParserMustParseEmptyArgs(t *testing.T) {
+	// this mirrors TestEmptyArgs
+	p, err := NewParser(Config{}, &struct{}{})
+	require.NoError(t, err)
+	assert.NotNil(t, p)
+	p.MustParse(nil)
+}
+
+func TestParserMustParse(t *testing.T) {
+	tests := []struct {
+		name    string
+		args    versioned
+		cmdLine []string
+		code    int
+		output  string
+	}{
+		{name: "help", args: struct{}{}, cmdLine: []string{"--help"}, code: 0, output: "display this help and exit"},
+		{name: "version", args: versioned{}, cmdLine: []string{"--version"}, code: 0, output: "example 3.2.1"},
+		{name: "invalid", args: struct{}{}, cmdLine: []string{"invalid"}, code: -1, output: ""},
+	}
+
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			originalExit := osExit
+			originalStdout := stdout
+			defer func() {
+				osExit = originalExit
+				stdout = originalStdout
+			}()
+
+			var exitCode *int
+			osExit = func(code int) { exitCode = &code }
+			var b bytes.Buffer
+			stdout = &b
+
+			p, err := NewParser(Config{}, &tt.args)
+			require.NoError(t, err)
+			assert.NotNil(t, p)
+
+			p.MustParse(tt.cmdLine)
+			assert.NotNil(t, exitCode)
+			assert.Equal(t, tt.code, *exitCode)
+			assert.Contains(t, b.String(), tt.output)
+		})
+	}
+}
+
 type textUnmarshaler struct {
 	val int
 }

usage.go

@@ -290,6 +290,10 @@ func (p *Parser) writeHelpForSubcommand(w io.Writer, cmd *command) {
 			printTwoCols(w, subcmd.name, subcmd.help, "", "")
 		}
 	}
+
+	if p.epilogue != "" {
+		fmt.Fprintln(w, "\n"+p.epilogue)
+	}
 }
 
 func (p *Parser) printOption(w io.Writer, spec *spec) {

usage_test.go

@@ -284,6 +284,37 @@ Options:
 	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 {