add RequiredFlagsErrorFunc and FlagGroupsErrorFunc

command.go

@@ -149,6 +149,12 @@ type Command struct {
 	// flagErrorFunc is func defined by user and it's called when the parsing of
 	// flags returns an error.
 	flagErrorFunc func(*Command, error) error
+	// requiredFlagErrorFunc is func defined by user and it's called when the parsing of
+	// required flags returns an error.
+	requiredFlagErrorFunc func(*Command, error) error
+	// flagGroupsErrorFunc is func defined by user and it's called when the parsing of
+	// required flags returns an error.
+	flagGroupsErrorFunc func(*Command, error) error
 	// helpTemplate is help template defined by user.
 	helpTemplate string
 	// helpFunc is help func defined by user.
@@ -283,12 +289,6 @@ func (c *Command) SetUsageTemplate(s string) {
 	c.usageTemplate = s
 }
 
-// SetFlagErrorFunc sets a function to generate an error when flag parsing
-// fails.
-func (c *Command) SetFlagErrorFunc(f func(*Command, error) error) {
-	c.flagErrorFunc = f
-}
-
 // SetHelpFunc sets help function. Can be defined by Application.
 func (c *Command) SetHelpFunc(f func(*Command, []string)) {
 	c.helpFunc = f
@@ -444,6 +444,12 @@ func (c *Command) UsageString() string {
 	return bb.String()
 }
 
+// SetFlagErrorFunc sets a function to generate an error when flag parsing
+// fails.
+func (c *Command) SetFlagErrorFunc(f func(*Command, error) error) {
+	c.flagErrorFunc = f
+}
+
 // FlagErrorFunc returns either the function set by SetFlagErrorFunc for this
 // command or a parent, or it returns a function which returns the original
 // error.
@@ -451,7 +457,6 @@ func (c *Command) FlagErrorFunc() (f func(*Command, error) error) {
 	if c.flagErrorFunc != nil {
 		return c.flagErrorFunc
 	}
-
 	if c.HasParent() {
 		return c.parent.FlagErrorFunc()
 	}
@@ -460,6 +465,48 @@ func (c *Command) FlagErrorFunc() (f func(*Command, error) error) {
 	}
 }
 
+// SetRequiredFlagsErrorFunc sets a function to generate an error when
+// validating of required flags fails.
+func (c *Command) SetRequiredFlagsErrorFunc(f func(*Command, error) error) {
+	c.requiredFlagErrorFunc = f
+}
+
+// RequiredFlagsErrorFunc returns either the function set by
+// SetRequiredFlagsErrorFunc for this command or a parent, or it returns a
+// function which returns the original error.
+func (c *Command) RequiredFlagsErrorFunc() (f func(*Command, error) error) {
+	if c.requiredFlagErrorFunc != nil {
+		return c.requiredFlagErrorFunc
+	}
+	if c.HasParent() {
+		return c.parent.RequiredFlagsErrorFunc()
+	}
+	return func(c *Command, err error) error {
+		return err
+	}
+}
+
+// SetFlagGroupsErrorFunc sets a function to generate an error when validating
+// of flag groups fails.
+func (c *Command) SetFlagGroupsErrorFunc(f func(*Command, error) error) {
+	c.flagGroupsErrorFunc = f
+}
+
+// FlagGroupsErrorFunc returns either the function set by
+// SetFlagGroupsErrorFunc for this command or a parent, or it returns a
+// function which returns the original error.
+func (c *Command) FlagGroupsErrorFunc() (f func(*Command, error) error) {
+	if c.flagGroupsErrorFunc != nil {
+		return c.flagGroupsErrorFunc
+	}
+	if c.HasParent() {
+		return c.parent.FlagGroupsErrorFunc()
+	}
+	return func(c *Command, err error) error {
+		return err
+	}
+}
+
 var minUsagePadding = 25
 
 // UsagePadding return padding for the usage.
@@ -861,10 +908,10 @@ func (c *Command) execute(a []string) (err error) {
 	}
 
 	if err := c.validateRequiredFlags(); err != nil {
-		return c.FlagErrorFunc()(c, err)
+		return c.RequiredFlagsErrorFunc()(c, err)
 	}
 	if err := c.validateFlagGroups(); err != nil {
-		return c.FlagErrorFunc()(c, err)
+		return c.FlagGroupsErrorFunc()(c, err)
 	}
 
 	if c.RunE != nil {

command_test.go

@@ -1723,6 +1723,74 @@ func TestFlagErrorFunc(t *testing.T) {
 	}
 }
 
+func TestRequiredFlagsErrorFunc(t *testing.T) {
+	c := &Command{Use: "c", Run: emptyRun}
+	ff := c.Flags()
+	ff.Bool("required-flag-1", false, "required flag #1")
+	ff.Bool("required-flag-2", false, "required flag #1")
+	if err := c.MarkFlagRequired("required-flag-1"); err != nil {
+		t.Errorf("unexpected error %v", err)
+	}
+	if err := c.MarkFlagRequired("required-flag-2"); err != nil {
+		t.Errorf("unexpected error %v", err)
+	}
+
+	expectedFmt := "This is expected: %v"
+	c.SetRequiredFlagsErrorFunc(func(_ *Command, err error) error {
+		return fmt.Errorf(expectedFmt, err)
+	})
+
+	_, err := executeCommand(c)
+
+	got := err.Error()
+	expected := fmt.Sprintf(expectedFmt, `required flag(s) "required-flag-1", "required-flag-2" not set`)
+	if got != expected {
+		t.Errorf("Expected %v, got %v", expected, got)
+	}
+}
+
+func TestFlagGroupsErrorFunc_RequiredTogether(t *testing.T) {
+	c := &Command{Use: "c", Run: emptyRun}
+	ff := c.Flags()
+	ff.Bool("required-flag-1", false, "required flag #1")
+	ff.Bool("required-flag-2", false, "required flag #1")
+	c.MarkFlagsRequiredTogether("required-flag-1", "required-flag-2")
+
+	expectedFmt := "This is expected: %v"
+	c.SetFlagGroupsErrorFunc(func(_ *Command, err error) error {
+		return fmt.Errorf(expectedFmt, err)
+	})
+
+	_, err := executeCommand(c, "--required-flag-1")
+
+	got := err.Error()
+	expected := fmt.Sprintf(expectedFmt, `if any flags in the group [required-flag-1 required-flag-2] are set they must all be set; missing [required-flag-2]`)
+	if got != expected {
+		t.Errorf("Expected %v, got %v", expected, got)
+	}
+}
+
+func TestFlagGroupsErrorFunc_MutuallyExclusive(t *testing.T) {
+	c := &Command{Use: "c", Run: emptyRun}
+	ff := c.Flags()
+	ff.Bool("required-flag-1", false, "required flag #1")
+	ff.Bool("required-flag-2", false, "required flag #1")
+	c.MarkFlagsMutuallyExclusive("required-flag-1", "required-flag-2")
+
+	expectedFmt := "This is expected: %v"
+	c.SetFlagGroupsErrorFunc(func(_ *Command, err error) error {
+		return fmt.Errorf(expectedFmt, err)
+	})
+
+	_, err := executeCommand(c, "--required-flag-1", "--required-flag-2")
+
+	got := err.Error()
+	expected := fmt.Sprintf(expectedFmt, `if any flags in the group [required-flag-1 required-flag-2] are set none of the others can be; [required-flag-1 required-flag-2] were all set`)
+	if got != expected {
+		t.Errorf("Expected %v, got %v", expected, got)
+	}
+}
+
 // TestSortedFlags checks,
 // if cmd.LocalFlags() is unsorted when cmd.Flags().SortFlags set to false.
 // Related to https://github.com/spf13/cobra/issues/404.