feat: Use struct error for errors returned in flag validation

command.go

@@ -1195,7 +1195,9 @@ func (c *Command) ValidateRequiredFlags() error {
 	})
 
 	if len(missingFlagNames) > 0 {
-		return fmt.Errorf(`required flag(s) "%s" not set`, strings.Join(missingFlagNames, `", "`))
+		return &RequiredFlagError{
+			missingFlagNames: missingFlagNames,
+		}
 	}
 	return nil
 }

errors.go

@@ -14,7 +14,10 @@
 
 package cobra
 
-import "fmt"
+import (
+	"fmt"
+	"strings"
+)
 
 // InvalidArgCountError is the error returned when the wrong number of arguments
 // are supplied to a command.
@@ -67,3 +70,44 @@ type UnknownSubcommandError struct {
 func (e *UnknownSubcommandError) Error() string {
 	return fmt.Sprintf("unknown command %q for %q%s", e.subcmd, e.cmd.CommandPath(), e.suggestions)
 }
+
+// RequiredFlagError is the error returned when a required flag is not set.
+type RequiredFlagError struct {
+	missingFlagNames []string
+}
+
+// Error implements error.
+func (e *RequiredFlagError) Error() string {
+	return fmt.Sprintf(`required flag(s) "%s" not set`, strings.Join(e.missingFlagNames, `", "`))
+}
+
+// FlagGroupError is the error returned when mutually-required or
+// mutually-exclusive flags are not properly specified.
+type FlagGroupError struct {
+	flagList      string
+	flagGroupType flagGroupType
+	problemFlags  []string
+}
+
+// flagGroupType identifies which failed validation caused a FlagGroupError.
+type flagGroupType string
+
+const (
+	flagGroupIsExclusive   flagGroupType = "if any is set, none of the others can be"
+	flagGroupIsRequired    flagGroupType = "if any is set, they must all be set"
+	flagGroupIsOneRequired flagGroupType = "at least one of the flags is required"
+)
+
+// Error implements error.
+func (e *FlagGroupError) Error() string {
+	switch e.flagGroupType {
+	case flagGroupIsRequired:
+		return fmt.Sprintf("if any flags in the group [%v] are set they must all be set; missing %v", e.flagList, e.problemFlags)
+	case flagGroupIsOneRequired:
+		return fmt.Sprintf("at least one of the flags in the group [%v] is required", e.flagList)
+	case flagGroupIsExclusive:
+		return fmt.Sprintf("if any flags in the group [%v] are set none of the others can be; %v were all set", e.flagList, e.problemFlags)
+	}
+
+	panic("invalid flagGroupType")
+}

flag_groups.go

@@ -158,7 +158,11 @@ func validateRequiredFlagGroups(data map[string]map[string]bool) error {
 
 		// Sort values, so they can be tested/scripted against consistently.
 		sort.Strings(unset)
-		return fmt.Errorf("if any flags in the group [%v] are set they must all be set; missing %v", flagList, unset)
+		return &FlagGroupError{
+			flagList:      flagList,
+			flagGroupType: flagGroupIsRequired,
+			problemFlags:  unset,
+		}
 	}
 
 	return nil
@@ -180,7 +184,10 @@ func validateOneRequiredFlagGroups(data map[string]map[string]bool) error {
 
 		// Sort values, so they can be tested/scripted against consistently.
 		sort.Strings(set)
-		return fmt.Errorf("at least one of the flags in the group [%v] is required", flagList)
+		return &FlagGroupError{
+			flagList:      flagList,
+			flagGroupType: flagGroupIsOneRequired,
+		}
 	}
 	return nil
 }
@@ -201,7 +208,11 @@ func validateExclusiveFlagGroups(data map[string]map[string]bool) error {
 
 		// Sort values, so they can be tested/scripted against consistently.
 		sort.Strings(set)
-		return fmt.Errorf("if any flags in the group [%v] are set none of the others can be; %v were all set", flagList, set)
+		return &FlagGroupError{
+			flagList:      flagList,
+			flagGroupType: flagGroupIsExclusive,
+			problemFlags:  set,
+		}
 	}
 	return nil
 }