2 files changed, 86 insertions, 0 deletions

diff --git a/unpack-trees.c b/unpack-trees.c
index 4733e7eaf8..a5bc0a3a16 100644
--- a/unpack-trees.c
+++ b/unpack-trees.c
@@ -1714,6 +1714,83 @@ return_failed:
 	goto done;
 }
 
+/*
+ * Update SKIP_WORKTREE bits according to sparsity patterns, and update
+ * working directory to match.
+ *
+ * CE_NEW_SKIP_WORKTREE is used internally.
+ */
+enum update_sparsity_result update_sparsity(struct unpack_trees_options *o)
+{
+	enum update_sparsity_result ret = UPDATE_SPARSITY_SUCCESS;
+	struct pattern_list pl;
+	int i, empty_worktree;
+	unsigned old_show_all_errors;
+	int free_pattern_list = 0;
+
+	old_show_all_errors = o->show_all_errors;
+	o->show_all_errors = 1;
+
+	/* Sanity checks */
+	if (!o->update || o->index_only || o->skip_sparse_checkout)
+		BUG("update_sparsity() is for reflecting sparsity patterns in working directory");
+	if (o->src_index != o->dst_index || o->fn)
+		BUG("update_sparsity() called wrong");
+
+	trace_performance_enter();
+
+	/* If we weren't given patterns, use the recorded ones */
+	if (!o->pl) {
+		memset(&pl, 0, sizeof(pl));
+		free_pattern_list = 1;
+		populate_from_existing_patterns(o, &pl);
+		if (o->skip_sparse_checkout)
+			goto skip_sparse_checkout;
+	}
+
+	/* Set NEW_SKIP_WORKTREE on existing entries. */
+	mark_all_ce_unused(o->src_index);
+	mark_new_skip_worktree(o->pl, o->src_index, 0,
+			       CE_NEW_SKIP_WORKTREE, o->verbose_update);
+
+	/* Then loop over entries and update/remove as needed */
+	ret = UPDATE_SPARSITY_SUCCESS;
+	empty_worktree = 1;
+	for (i = 0; i < o->src_index->cache_nr; i++) {
+		struct cache_entry *ce = o->src_index->cache[i];
+
+		if (apply_sparse_checkout(o->src_index, ce, o))
+			ret = UPDATE_SPARSITY_WARNINGS;
+
+		if (!ce_skip_worktree(ce))
+			empty_worktree = 0;
+	}
+
+	/*
+	 * Sparse checkout is meant to narrow down checkout area
+	 * but it does not make sense to narrow down to empty working
+	 * tree. This is usually a mistake in sparse checkout rules.
+	 * Do not allow users to do that.
+	 */
+	if (o->src_index->cache_nr && empty_worktree) {
+		unpack_failed(o, "Sparse checkout leaves no entry on working directory");
+		ret = UPDATE_SPARSITY_INDEX_UPDATE_FAILURES;
+		goto done;
+	}
+
+skip_sparse_checkout:
+	if (check_updates(o, o->src_index))
+		ret = UPDATE_SPARSITY_WORKTREE_UPDATE_FAILURES;
+
+done:
+	display_error_msgs(o);
+	o->show_all_errors = old_show_all_errors;
+	if (free_pattern_list)
+		clear_pattern_list(&pl);
+	trace_performance_leave("update_sparsity");
+	return ret;
+}
+
 /* Here come the merge functions */
 
 static int reject_merge(const struct cache_entry *ce,
diff --git a/unpack-trees.h b/unpack-trees.h
index d3516267f3..5cf41ef5b5 100644
--- a/unpack-trees.h
+++ b/unpack-trees.h
@@ -88,6 +88,15 @@ struct unpack_trees_options {
 int unpack_trees(unsigned n, struct tree_desc *t,
 		 struct unpack_trees_options *options);
 
+enum update_sparsity_result {
+	UPDATE_SPARSITY_SUCCESS = 0,
+	UPDATE_SPARSITY_WARNINGS = 1,
+	UPDATE_SPARSITY_INDEX_UPDATE_FAILURES = -1,
+	UPDATE_SPARSITY_WORKTREE_UPDATE_FAILURES = -2
+};
+
+enum update_sparsity_result update_sparsity(struct unpack_trees_options *options);
+
 int verify_uptodate(const struct cache_entry *ce,
 		    struct unpack_trees_options *o);