copies: pass changectx instead of manifest to _computenonoverlap The _computenonoverlap function takes two manifests to allow extensions to hook in and read the manifest nodes produced by the function. The remotefilelog extension actually needs the entire changectx instead (which includes the manifest) so it can prefetch the subset of files necessary for a sparse checkout (and the sparse checkout depends on which commit is being accessed, hence the need for the changectx). I have tests in the remotefilelog extension that cover this.