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/node_file.go

@@ -0,0 +1,54 @@
+package taskfile
+
+import (
+	"context"
+	"io"
+	"os"
+	"path/filepath"
+
+	"github.com/go-task/task/v3/internal/filepathext"
+)
+
+// A FileNode is a node that reads a taskfile from the local filesystem.
+type FileNode struct {
+	*BaseNode
+	Dir        string
+	Entrypoint string
+}
+
+func NewFileNode(uri string, opts ...NodeOption) (*FileNode, error) {
+	base := NewBaseNode(opts...)
+	if uri == "" {
+		d, err := os.Getwd()
+		if err != nil {
+			return nil, err
+		}
+		uri = d
+	}
+	path, err := Exists(uri)
+	if err != nil {
+		return nil, err
+	}
+	return &FileNode{
+		BaseNode:   base,
+		Dir:        filepath.Dir(path),
+		Entrypoint: filepath.Base(path),
+	}, nil
+}
+
+func (node *FileNode) Location() string {
+	return filepathext.SmartJoin(node.Dir, node.Entrypoint)
+}
+
+func (node *FileNode) Remote() bool {
+	return false
+}
+
+func (node *FileNode) Read(ctx context.Context) ([]byte, error) {
+	f, err := os.Open(node.Location())
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	return io.ReadAll(f)
+}