[PATCH 4/7] sparse-checkout: error or warn when given individual files

["Elijah Newren via GitGitGadget" <gitgitgadget@gmail.com>]

From: Elijah Newren <newren@gmail.com>

The set and add subcommands accept multiple positional arguments.
The meaning of these arguments differs slightly in the two modes:

Cone mode only accepts directories.  If given a file, it would
previously treat it as a directory, causing not just the file itself to
be included but all sibling files as well -- likely against users'
expectations.  Throw an error if the specified path is a file in the
index.  Provide a --skip-checks argument to allow users to override
(e.g. for the case when the given path IS a directory on another
branch).

Non-cone mode accepts general gitignore patterns.  However, it has an
O(N*M) performance baked into its design, where all N index files must
be matched against all M sparse-checkout patterns with EVERY call to
unpack_trees() that updates the working tree.  As such, it is important
to keep the number of patterns small, and thus we should warn users to
prefer passing directories and more generic glob patterns to get the
paths they want instead of listing each individual file.  (The
--skip-checks argument can also be used to bypass this warning.)  Also,
even when users do want to specify individual files, they will often
want to do so by providing a leading '/' (to avoid selecting the same
filename in all subdirectories), in which case this error message would
never trigger anyway.

Signed-off-by: Elijah Newren <newren@gmail.com>
---
 builtin/sparse-checkout.c          | 43 +++++++++++++++++++++++++-----
 t/t1091-sparse-checkout-builtin.sh | 16 ++++++++++-
 2 files changed, 52 insertions(+), 7 deletions(-)

diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
index bec423d5af9..8f8d2bd6ba5 100644
--- a/builtin/sparse-checkout.c
+++ b/builtin/sparse-checkout.c
@@ -1,4 +1,5 @@
 #include "builtin.h"
+#include "cache.h"
 #include "config.h"
 #include "dir.h"
 #include "parse-options.h"
@@ -681,8 +682,11 @@ static int modify_pattern_list(int argc, const char **argv, int use_stdin,
 	return result;
 }
 
-static void sanitize_paths(int argc, const char **argv, const char *prefix)
+static void sanitize_paths(int argc, const char **argv,
+			   const char *prefix, int skip_checks)
 {
+	int i;
+
 	if (!argc)
 		return;
 
@@ -691,26 +695,49 @@ static void sanitize_paths(int argc, const char **argv, const char *prefix)
 		 * The args are not pathspecs, so unfortunately we
 		 * cannot imitate how cmd_add() uses parse_pathspec().
 		 */
-		int i;
 		int prefix_len = strlen(prefix);
 
 		for (i = 0; i < argc; i++)
 			argv[i] = prefix_path(prefix, prefix_len, argv[i]);
 	}
+
+	if (skip_checks)
+		return;
+
+	for (i = 0; i < argc; i++) {
+		struct cache_entry *ce;
+		struct index_state *index = the_repository->index;
+		int pos = index_name_pos(index, argv[i], strlen(argv[i]));
+
+		if (pos < 0)
+			continue;
+		ce = index->cache[pos];
+		if (S_ISSPARSEDIR(ce->ce_mode))
+			continue;
+
+		if (core_sparse_checkout_cone)
+			die(_("\"%s\" is not a directory; to treat it as a directory anyway, rerun with --skip-checks"), argv[i]);
+		else
+			warning(_("path \"%s\" is an individual file; passing directories or less specific patterns is recommended (see NON-CONE PROBLEMS in the git-sparse-checkout manual)."), argv[i]);
+	}
 }
 
 static char const * const builtin_sparse_checkout_add_usage[] = {
-	N_("git sparse-checkout add (--stdin | <patterns>)"),
+	N_("git sparse-checkout add [--skip-checks] (--stdin | <patterns>)"),
 	NULL
 };
 
 static struct sparse_checkout_add_opts {
+	int skip_checks;
 	int use_stdin;
 } add_opts;
 
 static int sparse_checkout_add(int argc, const char **argv, const char *prefix)
 {
 	static struct option builtin_sparse_checkout_add_options[] = {
+		OPT_BOOL_F(0, "skip-checks", &add_opts.skip_checks,
+			   N_("skip some sanity checks on the given paths that might give false positives"),
+			   PARSE_OPT_NONEG),
 		OPT_BOOL(0, "stdin", &add_opts.use_stdin,
 			 N_("read patterns from standard in")),
 		OPT_END(),
@@ -726,19 +753,20 @@ static int sparse_checkout_add(int argc, const char **argv, const char *prefix)
 			     builtin_sparse_checkout_add_usage,
 			     PARSE_OPT_KEEP_UNKNOWN);
 
-	sanitize_paths(argc, argv, prefix);
+	sanitize_paths(argc, argv, prefix, add_opts.skip_checks);
 
 	return modify_pattern_list(argc, argv, add_opts.use_stdin, ADD);
 }
 
 static char const * const builtin_sparse_checkout_set_usage[] = {
-	N_("git sparse-checkout set [--[no-]cone] [--[no-]sparse-index] (--stdin | <patterns>)"),
+	N_("git sparse-checkout set [--[no-]cone] [--[no-]sparse-index] [--skip-checks] (--stdin | <patterns>)"),
 	NULL
 };
 
 static struct sparse_checkout_set_opts {
 	int cone_mode;
 	int sparse_index;
+	int skip_checks;
 	int use_stdin;
 } set_opts;
 
@@ -752,6 +780,9 @@ static int sparse_checkout_set(int argc, const char **argv, const char *prefix)
 			 N_("initialize the sparse-checkout in cone mode")),
 		OPT_BOOL(0, "sparse-index", &set_opts.sparse_index,
 			 N_("toggle the use of a sparse index")),
+		OPT_BOOL_F(0, "skip-checks", &set_opts.skip_checks,
+			   N_("skip some sanity checks on the given paths that might give false positives"),
+			   PARSE_OPT_NONEG),
 		OPT_BOOL_F(0, "stdin", &set_opts.use_stdin,
 			   N_("read patterns from standard in"),
 			   PARSE_OPT_NONEG),
@@ -780,7 +811,7 @@ static int sparse_checkout_set(int argc, const char **argv, const char *prefix)
 		argv = default_patterns;
 		argc = default_patterns_nr;
 	} else {
-		sanitize_paths(argc, argv, prefix);
+		sanitize_paths(argc, argv, prefix, set_opts.skip_checks);
 	}
 
 	return modify_pattern_list(argc, argv, set_opts.use_stdin, REPLACE);
diff --git a/t/t1091-sparse-checkout-builtin.sh b/t/t1091-sparse-checkout-builtin.sh
index b9e6987f5a6..1d95fa47258 100755
--- a/t/t1091-sparse-checkout-builtin.sh
+++ b/t/t1091-sparse-checkout-builtin.sh
@@ -580,7 +580,7 @@ test_expect_success 'different sparse-checkouts with worktrees' '
 '
 
 test_expect_success 'set using filename keeps file on-disk' '
-	git -C repo sparse-checkout set a deep &&
+	git -C repo sparse-checkout set --skip-checks a deep &&
 	cat >expect <<-\EOF &&
 	/*
 	!/*/
@@ -843,4 +843,18 @@ test_expect_success 'add from subdir pays attention to prefix' '
 	test_cmp expect actual
 '
 
+test_expect_success 'by default, cone mode will error out when passed files' '
+	git -C repo sparse-checkout reapply --cone &&
+	test_must_fail git -C repo sparse-checkout add .gitignore 2>error &&
+
+	grep ".gitignore.*is not a directory" error
+'
+
+test_expect_success 'by default, non-cone mode will warn on individual files' '
+	git -C repo sparse-checkout reapply --no-cone &&
+	git -C repo sparse-checkout add .gitignore 2>warning &&
+
+	grep "passing directories or less specific patterns is recommended" warning
+'
+
 test_done
-- 
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