From b8de27655fa86a0f388c141d3693c6732a753eae Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Tue, 21 Apr 2026 21:41:17 +0530
Subject: [PATCH] Utility function to delete content of dir pointed to by open
 file

---
 tools/utils/rmtree.go      | 80 ++++++++++++++++++++++++++++++++++++++
 tools/utils/rmtree_test.go | 52 +++++++++++++++++++++++++
 2 files changed, 132 insertions(+)
 create mode 100644 tools/utils/rmtree.go
 create mode 100644 tools/utils/rmtree_test.go

diff --git a/tools/utils/rmtree.go b/tools/utils/rmtree.go
new file mode 100644
index 000000000..7e6402bff
--- /dev/null
+++ b/tools/utils/rmtree.go
@@ -0,0 +1,80 @@
+package utils
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"os"
+
+	"golang.org/x/sys/unix"
+)
+
+var _ = fmt.Print
+
+// RemoveChildren recursively removes all files and subdirectories
+// within the directory pointed to by dirFile. Removes all it can but returns
+// the first error, if any.
+func RemoveChildren(dirFile *os.File) error {
+	fd := int(dirFile.Fd())
+	var firstErr error
+
+	// Rewind directory pointer to ensure we start from the beginning
+	if _, err := dirFile.Seek(0, 0); err != nil {
+		return &os.PathError{Op: "seek", Path: dirFile.Name(), Err: err}
+	}
+
+	for {
+		// Read names in small chunks to handle very large directories
+		names, err := dirFile.Readdirnames(64)
+		if err != nil {
+			if errors.Is(err, io.EOF) {
+				break
+			}
+			if firstErr == nil {
+				firstErr = &os.PathError{Op: "readdirnames", Path: dirFile.Name(), Err: err}
+			}
+			break
+		}
+
+		for _, name := range names {
+			var stat unix.Stat_t
+			// Get file info relative to the parent FD
+			err := unix.Fstatat(fd, name, &stat, unix.AT_SYMLINK_NOFOLLOW)
+			if err != nil {
+				if firstErr == nil {
+					firstErr = &os.PathError{Op: "fstatat", Path: name, Err: err}
+				}
+				continue
+			}
+
+			if (stat.Mode & unix.S_IFMT) == unix.S_IFDIR {
+				// Open subdirectory relative to parent FD
+				childFd, err := unix.Openat(fd, name, unix.O_RDONLY|unix.O_DIRECTORY|unix.O_CLOEXEC, 0)
+				if err != nil {
+					if firstErr == nil {
+						firstErr = &os.PathError{Op: "openat", Path: name, Err: err}
+					}
+					continue
+				}
+
+				childFile := os.NewFile(uintptr(childFd), name)
+				if err := RemoveChildren(childFile); err != nil && firstErr == nil {
+					firstErr = err
+				}
+				childFile.Close()
+
+				// Remove the empty subdirectory
+				if err := unix.Unlinkat(fd, name, unix.AT_REMOVEDIR); err != nil && firstErr == nil {
+					firstErr = &os.PathError{Op: "unlinkat", Path: name, Err: err}
+				}
+			} else {
+				// Remove file/symlink
+				if err := unix.Unlinkat(fd, name, 0); err != nil && firstErr == nil {
+					firstErr = &os.PathError{Op: "unlinkat", Path: name, Err: err}
+				}
+			}
+		}
+	}
+	_, _ = dirFile.Seek(0, 0)
+	return firstErr
+}
diff --git a/tools/utils/rmtree_test.go b/tools/utils/rmtree_test.go
new file mode 100644
index 000000000..d76d3a8d6
--- /dev/null
+++ b/tools/utils/rmtree_test.go
@@ -0,0 +1,52 @@
+package utils
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestRemoveChildren(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	// Create nested structure
+	subDir := filepath.Join(tmpDir, "subdir")
+	os.Mkdir(subDir, 0755)
+	os.WriteFile(filepath.Join(tmpDir, "file1.txt"), []byte("data"), 0644)
+	os.WriteFile(filepath.Join(subDir, "file2.txt"), []byte("data"), 0644)
+
+	d, err := os.Open(tmpDir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer d.Close()
+
+	if err := RemoveChildren(d); err != nil {
+		t.Errorf("expected no error, got %v", err)
+	}
+
+	// Verify directory is empty
+	entries, _ := os.ReadDir(tmpDir)
+	if len(entries) != 0 {
+		t.Errorf("expected 0 entries, got %d", len(entries))
+	}
+}
+
+func TestRemoveChildren_FirstError(t *testing.T) {
+	tmpDir := t.TempDir()
+
+	// Create a read-only file to trigger an error on some systems
+	// (Note: Behavior varies by OS; this is a conceptual test for firstErr)
+	lockedFile := filepath.Join(tmpDir, "locked")
+	os.WriteFile(lockedFile, nil, 0000)
+
+	d, _ := os.Open(tmpDir)
+	defer d.Close()
+
+	err := RemoveChildren(d)
+	if err != nil {
+		if _, ok := err.(*os.PathError); !ok {
+			t.Errorf("expected *os.PathError, got %T", err)
+		}
+	}
+}