refactor: taskfile/ast package (#1450)

* refactor: ast package

* feat: read -> taskfile

* refactor: taskfile.Taskfile -> taskfile.Read

* refactor: move merge function back into taskfile package

* refactor: rename taskfile.go to read.go

taskfile/ast/dep.go

@@ -0,0 +1,53 @@
+package ast
+
+import (
+	"fmt"
+
+	"gopkg.in/yaml.v3"
+)
+
+// Dep is a task dependency
+type Dep struct {
+	Task   string
+	Vars   *Vars
+	Silent bool
+}
+
+func (d *Dep) DeepCopy() *Dep {
+	if d == nil {
+		return nil
+	}
+	return &Dep{
+		Task: d.Task,
+		Vars: d.Vars.DeepCopy(),
+	}
+}
+
+func (d *Dep) UnmarshalYAML(node *yaml.Node) error {
+	switch node.Kind {
+
+	case yaml.ScalarNode:
+		var task string
+		if err := node.Decode(&task); err != nil {
+			return err
+		}
+		d.Task = task
+		return nil
+
+	case yaml.MappingNode:
+		var taskCall struct {
+			Task   string
+			Vars   *Vars
+			Silent bool
+		}
+		if err := node.Decode(&taskCall); err != nil {
+			return err
+		}
+		d.Task = taskCall.Task
+		d.Vars = taskCall.Vars
+		d.Silent = taskCall.Silent
+		return nil
+	}
+
+	return fmt.Errorf("cannot unmarshal %s into dependency", node.ShortTag())
+}