rm: expand the index only when necessary

Remove the `ensure_full_index()` method so `git-rm` does not always
expand the index when the expansion is unnecessary, i.e. when
<pathspec> does not have any possibilities to match anything outside
of sparse-checkout definition.

Expand the index when the <pathspec> needs an expanded index, i.e. the
<pathspec> contains wildcard that may need a full-index or the
<pathspec> is simply outside of sparse-checkout definition.

Notice that the test 'rm pathspec expands index when necessary' in
t1092 *is* testing this code change behavior, though it will be marked
as 'test_expect_success' only in the next patch, where we officially
mark `command_requires_full_index = 0`, so the index does not expand
unless we tell it to do so.

Notice that because we also want `ensure_full_index` to record the
stdout and stderr from Git command, a corresponding modification
is also included in this patch. The reason we want the "sparse-index-out"
and "sparse-index-err", is that we need to make sure there is no error
from Git command itself, so we can rely on the `test_region` result
and determine if the index is expanded or not.

Helped-by: Victoria Dye <vdye@github.com>
Helped-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Shaoxuan Yuan <shaoxuan.yuan02@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rm.c

@@ -296,8 +296,9 @@ int cmd_rm(int argc, const char **argv, const char *prefix)
 
 	seen = xcalloc(pathspec.nr, 1);
 
-	/* TODO: audit for interaction with sparse-index. */
-	ensure_full_index(&the_index);
+	if (pathspec_needs_expanded_index(&the_index, &pathspec))
+		ensure_full_index(&the_index);
+
 	for (i = 0; i < active_nr; i++) {
 		const struct cache_entry *ce = active_cache[i];
 

t/t1092-sparse-checkout-compatibility.sh

@@ -1365,10 +1365,14 @@ ensure_not_expanded () {
 		shift &&
 		test_must_fail env \
 			GIT_TRACE2_EVENT="$(pwd)/trace2.txt" \
-			git -C sparse-index "$@" || return 1
+			git -C sparse-index "$@" \
+			>sparse-index-out \
+			2>sparse-index-error || return 1
 	else
 		GIT_TRACE2_EVENT="$(pwd)/trace2.txt" \
-			git -C sparse-index "$@" || return 1
+			git -C sparse-index "$@" \
+			>sparse-index-out \
+			2>sparse-index-error || return 1
 	fi &&
 	test_region ! index ensure_full_index trace2.txt
 }
@@ -1935,4 +1939,23 @@ test_expect_failure 'rm pathspec outside sparse definition' '
 	test_sparse_match git status --porcelain=v2
 '
 
+test_expect_failure 'rm pathspec expands index when necessary' '
+	init_repos &&
+
+	# in-cone pathspec (do not expand)
+	ensure_not_expanded rm "deep/deep*" &&
+	test_must_be_empty sparse-index-err &&
+
+	# out-of-cone pathspec (expand)
+	! ensure_not_expanded rm --sparse "folder1/a*" &&
+	test_must_be_empty sparse-index-err &&
+
+	# pathspec that should expand index
+	! ensure_not_expanded rm "*/a" &&
+	test_must_be_empty sparse-index-err &&
+
+	! ensure_not_expanded rm "**a" &&
+	test_must_be_empty sparse-index-err
+'
+
 test_done