utils.py: Use `onerror` in `_force_rmtree`

If we don't, and encounter a file we don't own, but have permission to
delete, we'll fail with EPERM, since we won't be able to change
permissions but will be able to delete it.

Instead, we now try to change permissions and remove a file *after* we
realize we couldn't at first.

1 files changed, 16 insertions, 11 deletions

diff --git a/src/buildstream/utils.py b/src/buildstream/utils.py
index b6716a29d..545816e89 100644
--- a/src/buildstream/utils.py
+++ b/src/buildstream/utils.py
@@ -819,20 +819,25 @@ def _remove_path_with_parents(basedir: Union[Path, str], path: Union[Path, str])
 
 # Recursively remove directories, ignoring file permissions as much as
 # possible.
-def _force_rmtree(rootpath, **kwargs):
+def _force_rmtree(rootpath):
+    def fix_permissions(function, path, info):
+        parent = os.path.dirname(path)
 
-    os.chmod(rootpath, 0o755)
-    for root, dirs, _ in os.walk(rootpath):
-        for d in dirs:
-            path = os.path.join(root, d.lstrip("/"))
-            if os.path.exists(path) and not os.path.islink(path):
-                try:
-                    os.chmod(path, 0o755)
-                except OSError as e:
-                    raise UtilError("Failed to ensure write permission on file '{}': {}".format(path, e))
+        try:
+            os.chmod(parent, 0o755)
+        except OSError as e:
+            raise UtilError("Failed to ensure write permission on directory '{}': {}".format(parent, e))
+
+        # Directories need to be removed with `rmdir`, though
+        # `os.path.isdir` will follow symlinks, so make sure it's
+        # not a symlink first
+        if not os.path.islink(path) and os.path.isdir(path):
+            os.rmdir(path)
+        else:
+            os.remove(path)
 
     try:
-        shutil.rmtree(rootpath, **kwargs)
+        shutil.rmtree(rootpath, onerror=fix_permissions)
     except OSError as e:
         raise UtilError("Failed to remove cache directory '{}': {}".format(rootpath, e))