Allow for pluggable flag-level help text formatting

by defining `cli.DefaultFlagStringFunc` with a default value that uses
`withEnvHint`, conditionally running a given flag's `FormatValueHelp` if
present.

Closes #257

CHANGELOG.md

@@ -3,6 +3,12 @@
 **ATTN**: This project uses [semantic versioning](http://semver.org/).
 
 ## [Unreleased]
+### Added
+- Pluggable flag-level help text rendering via `cli.DefaultFlagStringFunc`
+
+### Changed
+- `Float64Flag`, `IntFlag`, and `DurationFlag` default values are no longer
+quoted in help text output.
 
 ## [1.16.0] - 2016-05-02
 ### Added

flag.go

@@ -31,6 +31,8 @@ var HelpFlag = BoolFlag{
 	Usage: "show help",
 }
 
+var DefaultFlagStringFunc FlagStringFunc = flagStringer
+
 // Flag is a common interface related to parsing flags in cli.
 // For more advanced flag parsing techniques, it is recommended that
 // this interface be implemented.
@@ -77,8 +79,7 @@ type GenericFlag struct {
 // help text to the user (uses the String() method of the generic flag to show
 // the value)
 func (f GenericFlag) String() string {
-	placeholder, usage := unquoteUsage(f.Usage)
+	return DefaultFlagStringFunc(f)
-	return withEnvHint(f.EnvVar, fmt.Sprintf("%s %v\t%v", prefixedNames(f.Name, placeholder), f.FormatValueHelp(), usage))
 }
 
 func (f GenericFlag) FormatValueHelp() string {
@@ -146,10 +147,7 @@ type StringSliceFlag struct {
 
 // String returns the usage
 func (f StringSliceFlag) String() string {
-	firstName := strings.Trim(strings.Split(f.Name, ",")[0], " ")
+	return DefaultFlagStringFunc(f)
-	pref := prefixFor(firstName)
-	placeholder, usage := unquoteUsage(f.Usage)
-	return withEnvHint(f.EnvVar, fmt.Sprintf("%s [%v]\t%v", prefixedNames(f.Name, placeholder), pref+firstName+" option "+pref+firstName+" option", usage))
 }
 
 // Apply populates the flag given the flag set and environment
@@ -181,6 +179,12 @@ func (f StringSliceFlag) GetName() string {
 	return f.Name
 }
 
+func (f StringSliceFlag) FormatValueHelp() string {
+	firstName := strings.Trim(strings.Split(f.Name, ",")[0], " ")
+	pref := prefixFor(firstName)
+	return fmt.Sprintf("[%s%s option %s%s option]", pref, firstName, pref, firstName)
+}
+
 // StringSlice is an opaque type for []int to satisfy flag.Value
 type IntSlice []int
 
@@ -217,10 +221,7 @@ type IntSliceFlag struct {
 
 // String returns the usage
 func (f IntSliceFlag) String() string {
-	firstName := strings.Trim(strings.Split(f.Name, ",")[0], " ")
+	return DefaultFlagStringFunc(f)
-	pref := prefixFor(firstName)
-	placeholder, usage := unquoteUsage(f.Usage)
-	return withEnvHint(f.EnvVar, fmt.Sprintf("%s [%v]\t%v", prefixedNames(f.Name, placeholder), pref+firstName+" option "+pref+firstName+" option", usage))
 }
 
 // Apply populates the flag given the flag set and environment
@@ -255,6 +256,12 @@ func (f IntSliceFlag) GetName() string {
 	return f.Name
 }
 
+func (f IntSliceFlag) FormatValueHelp() string {
+	firstName := strings.Trim(strings.Split(f.Name, ",")[0], " ")
+	pref := prefixFor(firstName)
+	return fmt.Sprintf("[%s%s option %s%s option]", pref, firstName, pref, firstName)
+}
+
 // BoolFlag is a switch that defaults to false
 type BoolFlag struct {
 	Name        string
@@ -266,8 +273,7 @@ type BoolFlag struct {
 
 // String returns a readable representation of this value (for usage defaults)
 func (f BoolFlag) String() string {
-	placeholder, usage := unquoteUsage(f.Usage)
+	return DefaultFlagStringFunc(f)
-	return withEnvHint(f.EnvVar, fmt.Sprintf("%s\t%v", prefixedNames(f.Name, placeholder), usage))
 }
 
 // Apply populates the flag given the flag set and environment
@@ -311,8 +317,7 @@ type BoolTFlag struct {
 
 // String returns a readable representation of this value (for usage defaults)
 func (f BoolTFlag) String() string {
-	placeholder, usage := unquoteUsage(f.Usage)
+	return DefaultFlagStringFunc(f)
-	return withEnvHint(f.EnvVar, fmt.Sprintf("%s\t%v", prefixedNames(f.Name, placeholder), usage))
 }
 
 // Apply populates the flag given the flag set and environment
@@ -356,8 +361,7 @@ type StringFlag struct {
 
 // String returns the usage
 func (f StringFlag) String() string {
-	placeholder, usage := unquoteUsage(f.Usage)
+	return DefaultFlagStringFunc(f)
-	return withEnvHint(f.EnvVar, fmt.Sprintf("%s %v\t%v", prefixedNames(f.Name, placeholder), f.FormatValueHelp(), usage))
 }
 
 func (f StringFlag) FormatValueHelp() string {
@@ -406,8 +410,7 @@ type IntFlag struct {
 
 // String returns the usage
 func (f IntFlag) String() string {
-	placeholder, usage := unquoteUsage(f.Usage)
+	return DefaultFlagStringFunc(f)
-	return withEnvHint(f.EnvVar, fmt.Sprintf("%s \"%v\"\t%v", prefixedNames(f.Name, placeholder), f.Value, usage))
 }
 
 // Apply populates the flag given the flag set and environment
@@ -451,8 +454,7 @@ type DurationFlag struct {
 
 // String returns a readable representation of this value (for usage defaults)
 func (f DurationFlag) String() string {
-	placeholder, usage := unquoteUsage(f.Usage)
+	return DefaultFlagStringFunc(f)
-	return withEnvHint(f.EnvVar, fmt.Sprintf("%s \"%v\"\t%v", prefixedNames(f.Name, placeholder), f.Value, usage))
 }
 
 // Apply populates the flag given the flag set and environment
@@ -496,8 +498,7 @@ type Float64Flag struct {
 
 // String returns the usage
 func (f Float64Flag) String() string {
-	placeholder, usage := unquoteUsage(f.Usage)
+	return DefaultFlagStringFunc(f)
-	return withEnvHint(f.EnvVar, fmt.Sprintf("%s \"%v\"\t%v", prefixedNames(f.Name, placeholder), f.Value, usage))
 }
 
 // Apply populates the flag given the flag set and environment
@@ -595,3 +596,27 @@ func withEnvHint(envVar, str string) string {
 	}
 	return str + envText
 }
+
+func flagStringer(f Flag) string {
+	fv := reflect.ValueOf(f)
+	placeholder, usage := unquoteUsage(fv.FieldByName("Usage").String())
+
+	defaultValueString := ""
+	if val := fv.FieldByName("Value"); val.IsValid() {
+		defaultValueString = fmt.Sprintf("%v", val.Interface())
+	}
+
+	formatFunc := fv.MethodByName("FormatValueHelp")
+	if formatFunc.IsValid() {
+		defaultValueString = formatFunc.Call([]reflect.Value{})[0].String()
+	}
+
+	if len(defaultValueString) > 0 {
+		defaultValueString = " " + defaultValueString
+	}
+
+	return withEnvHint(fv.FieldByName("EnvVar").String(),
+		fmt.Sprintf("%s%v\t%v",
+			prefixedNames(fv.FieldByName("Name").String(), placeholder),
+			defaultValueString, usage))
+}

flag_test.go

@@ -7,6 +7,7 @@ import (
 	"runtime"
 	"strings"
 	"testing"
+	"time"
 )
 
 var boolFlagTests = []struct {
@@ -18,13 +19,12 @@ var boolFlagTests = []struct {
 }
 
 func TestBoolFlagHelpOutput(t *testing.T) {
-
 	for _, test := range boolFlagTests {
 		flag := BoolFlag{Name: test.name}
 		output := flag.String()
 
 		if output != test.expected {
-			t.Errorf("%s does not match %s", output, test.expected)
+			t.Errorf("%q does not match %q", output, test.expected)
 		}
 	}
 }
@@ -49,7 +49,7 @@ func TestStringFlagHelpOutput(t *testing.T) {
 		output := flag.String()
 
 		if output != test.expected {
-			t.Errorf("%s does not match %s", output, test.expected)
+			t.Errorf("%q does not match %q", output, test.expected)
 		}
 	}
 }
@@ -131,8 +131,8 @@ var intFlagTests = []struct {
 	name     string
 	expected string
 }{
-	{"help", "--help \"0\"\t"},
+	{"help", "--help 0\t"},
-	{"h", "-h \"0\"\t"},
+	{"h", "-h 0\t"},
 }
 
 func TestIntFlagHelpOutput(t *testing.T) {
@@ -168,18 +168,17 @@ var durationFlagTests = []struct {
 	name     string
 	expected string
 }{
-	{"help", "--help \"0\"\t"},
+	{"help", "--help 1s\t"},
-	{"h", "-h \"0\"\t"},
+	{"h", "-h 1s\t"},
 }
 
 func TestDurationFlagHelpOutput(t *testing.T) {
-
 	for _, test := range durationFlagTests {
-		flag := DurationFlag{Name: test.name}
+		flag := DurationFlag{Name: test.name, Value: 1 * time.Second}
 		output := flag.String()
 
 		if output != test.expected {
-			t.Errorf("%s does not match %s", output, test.expected)
+			t.Errorf("%q does not match %q", output, test.expected)
 		}
 	}
 }
@@ -249,18 +248,17 @@ var float64FlagTests = []struct {
 	name     string
 	expected string
 }{
-	{"help", "--help \"0\"\t"},
+	{"help", "--help 0.1\t"},
-	{"h", "-h \"0\"\t"},
+	{"h", "-h 0.1\t"},
 }
 
 func TestFloat64FlagHelpOutput(t *testing.T) {
-
 	for _, test := range float64FlagTests {
-		flag := Float64Flag{Name: test.name}
+		flag := Float64Flag{Name: test.name, Value: float64(0.1)}
 		output := flag.String()
 
 		if output != test.expected {
-			t.Errorf("%s does not match %s", output, test.expected)
+			t.Errorf("%q does not match %q", output, test.expected)
 		}
 	}
 }
@@ -292,7 +290,6 @@ var genericFlagTests = []struct {
 }
 
 func TestGenericFlagHelpOutput(t *testing.T) {
-
 	for _, test := range genericFlagTests {
 		flag := GenericFlag{Name: test.name, Value: test.value, Usage: "test flag"}
 		output := flag.String()

funcs.go

@@ -22,3 +22,7 @@ type CommandNotFoundFunc func(*Context, string)
 // original error messages.  If this function is not set, the "Incorrect usage"
 // is displayed and the execution is interrupted.
 type OnUsageErrorFunc func(context *Context, err error, isSubcommand bool) error
+
+// FlagStringFunc is used by the help generation to display a flag, which is
+// expected to be a single line.
+type FlagStringFunc func(Flag) string