Merge branch 'ds/sparse-index-ita-crash' into jch

A crash in the 'sparse-index' collapse code when encountering an
invalidated cache-tree node (due to an intent-to-add path) has been
fixed by avoiding collapsing such subtrees.

* ds/sparse-index-ita-crash:
  sparse-index: avoid crash on intent-to-add entry outside the cone

sparse-index.c

@@ -113,10 +113,17 @@ static int convert_to_sparse_rec(struct index_state *istate,
 			continue;
 		}
 
+		span = ct->down[pos]->cache_tree->entry_count;
+		if (span < 0) {
+			/* cache-tree entry is invalidated, cannot collapse. */
+			istate->cache[num_converted++] = ce;
+			i++;
+			continue;
+		}
+
 		strbuf_setlen(&child_path, 0);
 		strbuf_add(&child_path, ce->name, slash - ce->name + 1);
 
-		span = ct->down[pos]->cache_tree->entry_count;
 		count = convert_to_sparse_rec(istate,
 					      num_converted, i, i + span,
 					      child_path.buf, child_path.len,

t/t1092-sparse-checkout-compatibility.sh

@@ -384,6 +384,54 @@ test_expect_success 'add, commit, checkout' '
 	test_all_match git checkout -
 '
 
+test_expect_success 'intent-to-add entries outside sparse-checkout' '
+	init_repos &&
+
+	write_script edit-contents <<-\EOF &&
+	echo text >>$1
+	EOF
+
+	test_sparse_match git sparse-checkout set deep folder1 &&
+	run_on_sparse mkdir -p folder1 &&
+	run_on_all ../edit-contents folder1/newita &&
+	test_sparse_match git add -N folder1/newita &&
+
+	test_sparse_match git sparse-checkout set deep &&
+	test_sparse_match git status --porcelain=v2 &&
+	test_sparse_match git ls-files --stage
+'
+
+test_expect_success 'intent-to-add with --sparse outside sparse-checkout' '
+	init_repos &&
+
+	write_script edit-contents <<-\EOF &&
+	echo text >>$1
+	EOF
+
+	run_on_all mkdir -p folder1 &&
+	run_on_all ../edit-contents folder1/newita &&
+	test_all_match git add --sparse --intent-to-add folder1/newita &&
+
+	test_all_match git status --porcelain=v2 &&
+	test_all_match git ls-files --stage &&
+	test_all_match git diff --cached --stat &&
+
+	# Ensure sparse index stores correct sparse directories and
+	# intent-to-add path.
+	git -C sparse-index ls-files --format="%(path)" --sparse >out &&
+
+	# These paths should be present in index as-is.
+	test_grep "^before/\$" out &&
+	test_grep "^folder1/newita\$" out &&
+	test_grep "^folder2/\$" out &&
+	test_grep "^x/\$" out &&
+
+	# folder/0/ could theoretically be collapsed to a sparse
+	# directory entry, but the current implementation avoids the
+	# reduction because of folder1/newita
+	test_grep "^folder1/0/0/0\$" out
+'
+
 test_expect_success 'git add, checkout, and reset with -p' '
 	init_repos &&
 

t/t3705-add-sparse-checkout.sh

@@ -233,4 +233,30 @@ test_expect_success 'refuse to add non-skip-worktree file from sparse dir' '
 	test_cmp expect stderr
 '
 
+test_expect_success 'intent-to-add entry and sparse index' '
+	test_when_finished "git sparse-checkout disable" &&
+	test_when_finished "git reset --hard" &&
+
+	git sparse-checkout disable &&
+	mkdir -p in out &&
+	echo base >in/file &&
+	echo base >out/file &&
+	git add in/file out/file &&
+	git commit -m "in and out directories" &&
+
+	# enable sparse-checkout, but with all child directories.
+	git config index.sparse true &&
+	git sparse-checkout set in out &&
+
+	# create a new path and set intent-to-add bit
+	echo new >out/newita &&
+	git add -N out/newita &&
+
+	# collapse sparse-checkout, and make sure that the sparse index
+	# maintains the intent-to-add bit.
+	git sparse-checkout set in &&
+	git ls-files --error-unmatch out/newita &&
+	git status --porcelain
+'
+
 test_done