universe vendoring

Rather than injecting universe at runtime, this change will vendor
alpha.dagger.io in `cue.mod` directly.

Fixes #700

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

stdlib/stdlib.go

@@ -1,8 +1,13 @@
 package stdlib
 
 import (
+	"context"
 	"embed"
+	"fmt"
+	"io/fs"
+	"os"
 	"path"
+	"path/filepath"
 )
 
 var (
@@ -13,3 +18,38 @@ var (
 	PackageName = "alpha.dagger.io"
 	Path        = path.Join("cue.mod", "pkg", PackageName)
 )
+
+func Vendor(ctx context.Context, mod string) error {
+	// Remove any existing copy of the universe
+	if err := os.RemoveAll(path.Join(mod, Path)); err != nil {
+		return err
+	}
+
+	// Write the current version
+	return fs.WalkDir(FS, ".", func(p string, entry fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+
+		if !entry.Type().IsRegular() {
+			return nil
+		}
+
+		if filepath.Ext(entry.Name()) != ".cue" {
+			return nil
+		}
+
+		contents, err := fs.ReadFile(FS, p)
+		if err != nil {
+			return fmt.Errorf("%s: %w", p, err)
+		}
+
+		overlayPath := path.Join(mod, Path, p)
+
+		if err := os.MkdirAll(filepath.Dir(overlayPath), 0755); err != nil {
+			return err
+		}
+
+		return os.WriteFile(overlayPath, contents, 0600)
+	})
+}