update: do not try to copy a dir in the ESP if it does not exists

When doing removals, usually copy direcory to temp direcoty, then
do operations in temp dir, but should check if the dir is existed
 in dest ESP.

Fixes #856

Author: HuijingHei

src/filetree.rs

@@ -339,8 +339,11 @@ pub(crate) fn apply_diff(
             if first_dir != path {
                 path_tmp = Utf8Path::new(&first_dir_tmp).join(path.strip_prefix(&first_dir)?);
                 // copy to temp dir and remember
-                if !destdir.exists(&first_dir_tmp)? {
-                    copy_dir(destdir, first_dir.as_str(), &first_dir_tmp)?;
+                // skip copying if dir not existed in dest
+                if !destdir.exists(&first_dir_tmp)? && destdir.exists(first_dir.as_std_path())? {
+                    copy_dir(destdir, first_dir.as_str(), &first_dir_tmp).with_context(|| {
+                        format!("copy {first_dir} to {first_dir_tmp} before removing {pathstr}")
+                    })?;
                     updates.insert(first_dir, first_dir_tmp);
                 }
             } else {
@@ -359,7 +362,9 @@ pub(crate) fn apply_diff(
         if first_dir != path {
             if !destdir.exists(&first_dir_tmp)? && destdir.exists(first_dir.as_std_path())? {
                 // copy to temp dir if not exists
-                copy_dir(destdir, first_dir.as_str(), &first_dir_tmp)?;
+                copy_dir(destdir, first_dir.as_str(), &first_dir_tmp).with_context(|| {
+                    format!("copy {first_dir} to {first_dir_tmp} before updating {pathstr}")
+                })?;
             }
             path_tmp = path_tmp.join(path.strip_prefix(&first_dir)?);
             // ensure new additions dir exists