Adding Int64Flag type and related tests

flag.go

@@ -420,6 +420,51 @@ func (f IntFlag) GetName() string {
 	return f.Name
 }
 
+// Int64Flag is a flag that takes a 64-bit integer
+// Errors if the value provided cannot be parsed
+type Int64Flag struct {
+	Name        string
+	Value       int64
+	Usage       string
+	EnvVar      string
+	Destination *int64
+	Hidden      bool
+}
+
+// String returns the usage
+func (f Int64Flag) String() string {
+	return FlagStringer(f)
+}
+
+// Apply populates the flag given the flag set and environment
+func (f Int64Flag) Apply(set *flag.FlagSet) {
+	if f.EnvVar != "" {
+		for _, envVar := range strings.Split(f.EnvVar, ",") {
+			envVar = strings.TrimSpace(envVar)
+			if envVal := os.Getenv(envVar); envVal != "" {
+				envValInt, err := strconv.ParseInt(envVal, 0, 64)
+				if err == nil {
+					f.Value = envValInt
+					break
+				}
+			}
+		}
+	}
+
+	eachName(f.Name, func(name string) {
+		if f.Destination != nil {
+			set.Int64Var(f.Destination, name, f.Value, f.Usage)
+			return
+		}
+		set.Int64(name, f.Value, f.Usage)
+	})
+}
+
+// GetName returns the name of the flag.
+func (f Int64Flag) GetName() string {
+	return f.Name
+}
+
 // DurationFlag is a flag that takes a duration specified in Go's duration
 // format: https://golang.org/pkg/time/#ParseDuration
 type DurationFlag struct {

flag_test.go

@@ -162,6 +162,42 @@ func TestIntFlagWithEnvVarHelpOutput(t *testing.T) {
 	}
 }
 
+var int64FlagTests = []struct {
+	name     string
+	expected string
+}{
+	{"hats", "--hats value\t(default: 8589934592)"},
+	{"H", "-H value\t(default: 8589934592)"},
+}
+
+func TestInt64FlagHelpOutput(t *testing.T) {
+	for _, test := range int64FlagTests {
+		flag := Int64Flag{Name: test.name, Value: 8589934592}
+		output := flag.String()
+
+		if output != test.expected {
+			t.Errorf("%s does not match %s", output, test.expected)
+		}
+	}
+}
+
+func TestInt64FlagWithEnvVarHelpOutput(t *testing.T) {
+	os.Clearenv()
+	os.Setenv("APP_BAR", "2")
+	for _, test := range int64FlagTests {
+		flag := IntFlag{Name: test.name, EnvVar: "APP_BAR"}
+		output := flag.String()
+
+		expectedSuffix := " [$APP_BAR]"
+		if runtime.GOOS == "windows" {
+			expectedSuffix = " [%APP_BAR%]"
+		}
+		if !strings.HasSuffix(output, expectedSuffix) {
+			t.Errorf("%s does not end with"+expectedSuffix, output)
+		}
+	}
+}
+
 var durationFlagTests = []struct {
 	name     string
 	expected string