sparse-checkout: pay attention to prefix for {set, add}

In cone mode, non-option arguments to set & add are clearly paths, and
as such, we should pay attention to prefix.

In non-cone mode, it is not clear that folks intend to provide paths
since the inputs are gitignore-style patterns.  Paying attention to
prefix would prevent folks from doing things like
   git sparse-checkout add /.gitattributes
   git sparse-checkout add '/toplevel-dir/*'
In fact, the former will result in
   fatal: '/.gitattributes' is outside repository...
while the later will result in
   fatal: Invalid path '/toplevel-dir': No such file or directory
despite the fact that both are valid gitignore-style patterns that would
select real files if added to the sparse-checkout file.  This might lead
people to just use the path without the leading slash, potentially
resulting in them grabbing files with the same name throughout the
directory hierarchy contrary to their expectations.  See also [1] and
[2].  Adding prefix seems to just be fraught with error; so for now
simply throw an error in non-cone mode when sparse-checkout set/add are
run from a subdirectory.

[1] https://lore.kernel.org/git/e1934710-e228-adc4-d37c-f706883bd27c@gmail.com/
[2] https://lore.kernel.org/git/CABPp-BHXZ-XLxY0a3wCATfdq=6-EjW62RzbxKAoFPeXfJswD2w@mail.gmail.com/

Helped-by: Junio Hamano <gitster@pobox.com>
Reviewed-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/sparse-checkout.c

@@ -684,6 +684,28 @@ 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)
+{
+	if (!argc)
+		return;
+
+	if (prefix && *prefix && core_sparse_checkout_cone) {
+		/*
+		 * 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 (prefix && *prefix && !core_sparse_checkout_cone)
+		die(_("please run from the toplevel directory in non-cone mode"));
+
+}
+
 static char const * const builtin_sparse_checkout_add_usage[] = {
 	N_("git sparse-checkout add (--stdin | <patterns>)"),
 	NULL
@@ -711,6 +733,8 @@ 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);
+
 	return modify_pattern_list(argc, argv, add_opts.use_stdin, ADD);
 }
 
@@ -762,6 +786,8 @@ static int sparse_checkout_set(int argc, const char **argv, const char *prefix)
 	if (!core_sparse_checkout_cone && argc == 0) {
 		argv = default_patterns;
 		argc = default_patterns_nr;
+	} else {
+		sanitize_paths(argc, argv, prefix);
 	}
 
 	return modify_pattern_list(argc, argv, set_opts.use_stdin, REPLACE);

t/t1091-sparse-checkout-builtin.sh

@@ -798,4 +798,45 @@ test_expect_success 'malformed cone-mode patterns' '
 	grep "warning: disabling cone pattern matching" err
 '
 
+test_expect_success 'set from subdir pays attention to prefix' '
+	git -C repo sparse-checkout disable &&
+	git -C repo/deep sparse-checkout set --cone deeper2 ../folder1 &&
+
+	git -C repo sparse-checkout list >actual &&
+
+	cat >expect <<-\EOF &&
+	deep/deeper2
+	folder1
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'add from subdir pays attention to prefix' '
+	git -C repo sparse-checkout set --cone deep/deeper2 &&
+	git -C repo/deep sparse-checkout add deeper1/deepest ../folder1 &&
+
+	git -C repo sparse-checkout list >actual &&
+
+	cat >expect <<-\EOF &&
+	deep/deeper1/deepest
+	deep/deeper2
+	folder1
+	EOF
+	test_cmp expect actual
+'
+
+test_expect_success 'set from subdir in non-cone mode throws an error' '
+	git -C repo sparse-checkout disable &&
+	test_must_fail git -C repo/deep sparse-checkout set --no-cone deeper2 ../folder1 2>error &&
+
+	grep "run from the toplevel directory in non-cone mode" error
+'
+
+test_expect_success 'set from subdir in non-cone mode throws an error' '
+	git -C repo sparse-checkout set --no-cone deep/deeper2 &&
+	test_must_fail git -C repo/deep sparse-checkout add deeper1/deepest ../folder1 2>error &&
+
+	grep "run from the toplevel directory in non-cone mode" error
+'
+
 test_done