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/output.go

@@ -0,0 +1,65 @@
+package ast
+
+import (
+	"fmt"
+
+	"gopkg.in/yaml.v3"
+)
+
+// Output of the Task output
+type Output struct {
+	// Name of the Output.
+	Name string `yaml:"-"`
+	// Group specific style
+	Group OutputGroup
+}
+
+// IsSet returns true if and only if a custom output style is set.
+func (s *Output) IsSet() bool {
+	return s.Name != ""
+}
+
+func (s *Output) UnmarshalYAML(node *yaml.Node) error {
+	switch node.Kind {
+
+	case yaml.ScalarNode:
+		var name string
+		if err := node.Decode(&name); err != nil {
+			return err
+		}
+		s.Name = name
+		return nil
+
+	case yaml.MappingNode:
+		var tmp struct {
+			Group *OutputGroup
+		}
+		if err := node.Decode(&tmp); err != nil {
+			return fmt.Errorf("task: output style must be a string or mapping with a \"group\" key: %w", err)
+		}
+		if tmp.Group == nil {
+			return fmt.Errorf("task: output style must have the \"group\" key when in mapping form")
+		}
+		*s = Output{
+			Name:  "group",
+			Group: *tmp.Group,
+		}
+		return nil
+	}
+
+	return fmt.Errorf("yaml: line %d: cannot unmarshal %s into output", node.Line, node.ShortTag())
+}
+
+// OutputGroup is the style options specific to the Group style.
+type OutputGroup struct {
+	Begin, End string
+	ErrorOnly  bool `yaml:"error_only"`
+}
+
+// IsSet returns true if and only if a custom output style is set.
+func (g *OutputGroup) IsSet() bool {
+	if g == nil {
+		return false
+	}
+	return g.Begin != "" || g.End != ""
+}