internal/pkg: expand single directory tarball

This enables much cleaner use of their output without giving up any meaningful data.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/tar.go

@@ -108,6 +108,10 @@ func (a *tarArtifact) Cure(work, temp *check.Absolute, loadData CacheDataFunc) (
 	}
 	var madeDirectories []dirTargetPerm
 
+	if err = os.MkdirAll(temp.String(), 0700); err != nil {
+		return
+	}
+
 	var header *tar.Header
 	r := tar.NewReader(tr)
 	for header, err = r.Next(); err == nil; header, err = r.Next() {
@@ -125,7 +129,7 @@ func (a *tarArtifact) Cure(work, temp *check.Absolute, loadData CacheDataFunc) (
 			case tar.TypeReg:
 				var f *os.File
 				if f, err = os.OpenFile(
-					work.Append(header.Name).String(),
+					temp.Append(header.Name).String(),
 					os.O_CREATE|os.O_EXCL|os.O_WRONLY,
 					header.FileInfo().Mode()&0400,
 				); err != nil {
@@ -142,7 +146,7 @@ func (a *tarArtifact) Cure(work, temp *check.Absolute, loadData CacheDataFunc) (
 			case tar.TypeLink:
 				if err = os.Link(
 					header.Linkname,
-					work.Append(header.Name).String(),
+					temp.Append(header.Name).String(),
 				); err != nil {
 					return
 				}
@@ -151,14 +155,14 @@ func (a *tarArtifact) Cure(work, temp *check.Absolute, loadData CacheDataFunc) (
 			case tar.TypeSymlink:
 				if err = os.Symlink(
 					header.Linkname,
-					work.Append(header.Name).String(),
+					temp.Append(header.Name).String(),
 				); err != nil {
 					return
 				}
 				break
 
 			case tar.TypeDir:
-				pathname := work.Append(header.Name)
+				pathname := temp.Append(header.Name)
 				madeDirectories = append(madeDirectories, dirTargetPerm{
 					path: pathname,
 					mode: header.FileInfo().Mode(),
@@ -185,14 +189,29 @@ func (a *tarArtifact) Cure(work, temp *check.Absolute, loadData CacheDataFunc) (
 	if errors.Is(err, io.EOF) {
 		err = nil
 	}
-
 	if err == nil {
 		for _, e := range madeDirectories {
 			if err = os.Chmod(e.path.String(), e.mode&0500); err != nil {
 				return
 			}
 		}
-		err = os.Chmod(work.String(), 0500)
+	} else {
+		return
+	}
+
+	var entries []os.DirEntry
+	if entries, err = os.ReadDir(temp.String()); err != nil {
+		return
+	}
+
+	if len(entries) == 1 && entries[0].IsDir() {
+		p := temp.Append(entries[0].Name())
+		if err = os.Chmod(p.String(), 0700); err != nil {
+			return
+		}
+		err = os.Rename(p.String(), work.String())
+	} else {
+		err = os.Rename(temp.String(), work.String())
 	}
 	return
 }