feat: option to ensure variable is within the list of values (#1827)

taskfile/ast/requires.go

@@ -1,10 +1,15 @@
 package ast
 
-import "github.com/go-task/task/v3/internal/deepcopy"
+import (
+	"gopkg.in/yaml.v3"
+
+	"github.com/go-task/task/v3/errors"
+	"github.com/go-task/task/v3/internal/deepcopy"
+)
 
 // Requires represents a set of required variables necessary for a task to run
 type Requires struct {
-	Vars []string
+	Vars []*VarsWithValidation
 }
 
 func (r *Requires) DeepCopy() *Requires {
@@ -16,3 +21,47 @@ func (r *Requires) DeepCopy() *Requires {
 		Vars: deepcopy.Slice(r.Vars),
 	}
 }
+
+type VarsWithValidation struct {
+	Name string
+	Enum []string
+}
+
+func (v *VarsWithValidation) DeepCopy() *VarsWithValidation {
+	if v == nil {
+		return nil
+	}
+	return &VarsWithValidation{
+		Name: v.Name,
+		Enum: v.Enum,
+	}
+}
+
+// UnmarshalYAML implements yaml.Unmarshaler interface.
+func (v *VarsWithValidation) UnmarshalYAML(node *yaml.Node) error {
+	switch node.Kind {
+
+	case yaml.ScalarNode:
+		var cmd string
+		if err := node.Decode(&cmd); err != nil {
+			return errors.NewTaskfileDecodeError(err, node)
+		}
+		v.Name = cmd
+		v.Enum = nil
+		return nil
+
+	case yaml.MappingNode:
+		var vv struct {
+			Name string
+			Enum []string
+		}
+		if err := node.Decode(&vv); err != nil {
+			return errors.NewTaskfileDecodeError(err, node)
+		}
+		v.Name = vv.Name
+		v.Enum = vv.Enum
+		return nil
+	}
+
+	return errors.NewTaskfileDecodeError(nil, node).WithTypeMessage("requires")
+}