[PATCH v4 6/7] add: warn when asked to update SKIP_WORKTREE entries

[Matheus Tavares <matheus.bernardino@usp.br>]

`git add` already refrains from updating SKIP_WORKTREE entries, but it
silently exits with zero code when it is asked to do so. Instead, let's
warn the user and display a hint on how to update these entries.

Note that we only warn the user whey they give a pathspec item that
matches no eligible path for updating, but it does match one or more
SKIP_WORKTREE entries. A warning was chosen over erroring out right away
to reproduce the same behavior `add` already exhibits with ignored
files. This also allow users to continue their workflow without having
to invoke `add` again with only the eligible paths (as those will have
already been added).

Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br>
---
 Documentation/config/advice.txt |  3 ++
 advice.c                        | 20 +++++++++
 advice.h                        |  4 ++
 builtin/add.c                   | 70 ++++++++++++++++++++++++-------
 pathspec.c                      | 15 +++++++
 pathspec.h                      |  8 ++++
 t/t3705-add-sparse-checkout.sh  | 73 +++++++++++++++++++++++++++++----
 7 files changed, 172 insertions(+), 21 deletions(-)

diff --git a/Documentation/config/advice.txt b/Documentation/config/advice.txt
index acbd0c09aa..851b83cf30 100644
--- a/Documentation/config/advice.txt
+++ b/Documentation/config/advice.txt
@@ -119,4 +119,7 @@ advice.*::
 	addEmptyPathspec::
 		Advice shown if a user runs the add command without providing
 		the pathspec parameter.
+	updateSparsePath::
+		Advice shown when linkgit:git-add[1] is asked to update index
+		entries outside the current sparse checkout.
 --
diff --git a/advice.c b/advice.c
index 164742305f..0b9c89c48a 100644
--- a/advice.c
+++ b/advice.c
@@ -2,6 +2,7 @@
 #include "config.h"
 #include "color.h"
 #include "help.h"
+#include "string-list.h"
 
 int advice_fetch_show_forced_updates = 1;
 int advice_push_update_rejected = 1;
@@ -136,6 +137,7 @@ static struct {
 	[ADVICE_STATUS_HINTS]				= { "statusHints", 1 },
 	[ADVICE_STATUS_U_OPTION]			= { "statusUoption", 1 },
 	[ADVICE_SUBMODULE_ALTERNATE_ERROR_STRATEGY_DIE] = { "submoduleAlternateErrorStrategyDie", 1 },
+	[ADVICE_UPDATE_SPARSE_PATH]			= { "updateSparsePath", 1 },
 	[ADVICE_WAITING_FOR_EDITOR]			= { "waitingForEditor", 1 },
 };
 
@@ -284,6 +286,24 @@ void NORETURN die_conclude_merge(void)
 	die(_("Exiting because of unfinished merge."));
 }
 
+void advise_on_updating_sparse_paths(struct string_list *pathspec_list)
+{
+	struct string_list_item *item;
+
+	if (!pathspec_list->nr)
+		return;
+
+	fprintf(stderr, _("The following pathspecs didn't match any"
+			  " eligible path, but they do match index\n"
+			  "entries outside the current sparse checkout:\n"));
+	for_each_string_list_item(item, pathspec_list)
+		fprintf(stderr, "%s\n", item->string);
+
+	advise_if_enabled(ADVICE_UPDATE_SPARSE_PATH,
+			  _("Disable or modify the sparsity rules if you intend"
+			    " to update such entries."));
+}
+
 void detach_advice(const char *new_name)
 {
 	const char *fmt =
diff --git a/advice.h b/advice.h
index bc2432980a..bd26c385d0 100644
--- a/advice.h
+++ b/advice.h
@@ -3,6 +3,8 @@
 
 #include "git-compat-util.h"
 
+struct string_list;
+
 extern int advice_fetch_show_forced_updates;
 extern int advice_push_update_rejected;
 extern int advice_push_non_ff_current;
@@ -71,6 +73,7 @@ extern int advice_add_empty_pathspec;
 	ADVICE_STATUS_HINTS,
 	ADVICE_STATUS_U_OPTION,
 	ADVICE_SUBMODULE_ALTERNATE_ERROR_STRATEGY_DIE,
+	ADVICE_UPDATE_SPARSE_PATH,
 	ADVICE_WAITING_FOR_EDITOR,
 };
 
@@ -92,6 +95,7 @@ void advise_if_enabled(enum advice_type type, const char *advice, ...);
 int error_resolve_conflict(const char *me);
 void NORETURN die_resolve_conflict(const char *me);
 void NORETURN die_conclude_merge(void);
+void advise_on_updating_sparse_paths(struct string_list *pathspec_list);
 void detach_advice(const char *new_name);
 
 #endif /* ADVICE_H */
diff --git a/builtin/add.c b/builtin/add.c
index 050cb8af30..6980311aaa 100644
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -178,24 +178,43 @@ static char *prune_directory(struct dir_struct *dir, struct pathspec *pathspec,
 	}
 	dir->nr = dst - dir->entries;
 	add_pathspec_matches_against_index(pathspec, &the_index, seen,
-					   PS_HEED_SKIP_WORKTREE);
+					   PS_IGNORE_SKIP_WORKTREE);
 	return seen;
 }
 
-static void refresh(int verbose, const struct pathspec *pathspec)
+static int refresh(int verbose, const struct pathspec *pathspec)
 {
 	char *seen;
-	int i;
+	int i, ret = 0;
+	char *skip_worktree_seen = NULL;
+	struct string_list only_match_skip_worktree = STRING_LIST_INIT_NODUP;
+	int flags = REFRESH_IGNORE_SKIP_WORKTREE |
+		    (verbose ? REFRESH_IN_PORCELAIN : REFRESH_QUIET);
 
 	seen = xcalloc(pathspec->nr, 1);
-	refresh_index(&the_index, verbose ? REFRESH_IN_PORCELAIN : REFRESH_QUIET,
-		      pathspec, seen, _("Unstaged changes after refreshing the index:"));
+	refresh_index(&the_index, flags, pathspec, seen,
+		      _("Unstaged changes after refreshing the index:"));
 	for (i = 0; i < pathspec->nr; i++) {
-		if (!seen[i])
-			die(_("pathspec '%s' did not match any files"),
-			    pathspec->items[i].original);
+		if (!seen[i]) {
+			if (matches_skip_worktree(pathspec, i, &skip_worktree_seen)) {
+				string_list_append(&only_match_skip_worktree,
+						   pathspec->items[i].original);
+			} else {
+				die(_("pathspec '%s' did not match any files"),
+				    pathspec->items[i].original);
+			}
+		}
+	}
+
+	if (only_match_skip_worktree.nr) {
+		advise_on_updating_sparse_paths(&only_match_skip_worktree);
+		ret = 1;
 	}
+
 	free(seen);
+	free(skip_worktree_seen);
+	string_list_clear(&only_match_skip_worktree, 0);
+	return ret;
 }
 
 int run_add_interactive(const char *revision, const char *patch_mode,
@@ -571,16 +590,18 @@ int cmd_add(int argc, const char **argv, const char *prefix)
 	}
 
 	if (refresh_only) {
-		refresh(verbose, &pathspec);
+		exit_status |= refresh(verbose, &pathspec);
 		goto finish;
 	}
 
 	if (pathspec.nr) {
 		int i;
+		char *skip_worktree_seen = NULL;
+		struct string_list only_match_skip_worktree = STRING_LIST_INIT_NODUP;
 
 		if (!seen)
 			seen = find_pathspecs_matching_against_index(&pathspec,
-					&the_index, PS_HEED_SKIP_WORKTREE);
+					&the_index, PS_IGNORE_SKIP_WORKTREE);
 
 		/*
 		 * file_exists() assumes exact match
@@ -594,12 +615,24 @@ int cmd_add(int argc, const char **argv, const char *prefix)
 
 		for (i = 0; i < pathspec.nr; i++) {
 			const char *path = pathspec.items[i].match;
+
 			if (pathspec.items[i].magic & PATHSPEC_EXCLUDE)
 				continue;
-			if (!seen[i] && path[0] &&
-			    ((pathspec.items[i].magic &
-			      (PATHSPEC_GLOB | PATHSPEC_ICASE)) ||
-			     !file_exists(path))) {
+			if (seen[i])
+				continue;
+
+			if (matches_skip_worktree(&pathspec, i, &skip_worktree_seen)) {
+				string_list_append(&only_match_skip_worktree,
+						   pathspec.items[i].original);
+				continue;
+			}
+
+			/* Don't complain at 'git add .' on empty repo */
+			if (!path[0])
+				continue;
+
+			if ((pathspec.items[i].magic & (PATHSPEC_GLOB | PATHSPEC_ICASE)) ||
+			    !file_exists(path)) {
 				if (ignore_missing) {
 					int dtype = DT_UNKNOWN;
 					if (is_excluded(&dir, &the_index, path, &dtype))
@@ -610,7 +643,16 @@ int cmd_add(int argc, const char **argv, const char *prefix)
 					    pathspec.items[i].original);
 			}
 		}
+
+
+		if (only_match_skip_worktree.nr) {
+			advise_on_updating_sparse_paths(&only_match_skip_worktree);
+			exit_status = 1;
+		}
+
 		free(seen);
+		free(skip_worktree_seen);
+		string_list_clear(&only_match_skip_worktree, 0);
 	}
 
 	plug_bulk_checkin();
diff --git a/pathspec.c b/pathspec.c
index 8b05575110..ab67ff7c5c 100644
--- a/pathspec.c
+++ b/pathspec.c
@@ -62,6 +62,21 @@ char *find_pathspecs_matching_against_index(const struct pathspec *pathspec,
 	return seen;
 }
 
+char *find_pathspecs_matching_skip_worktree(const struct pathspec *pathspec)
+{
+	struct index_state *istate = the_repository->index;
+	char *seen = xcalloc(pathspec->nr, 1);
+	int i;
+
+	for (i = 0; i < istate->cache_nr; i++) {
+		struct cache_entry *ce = istate->cache[i];
+		if (ce_skip_worktree(ce))
+		    ce_path_match(istate, ce, pathspec, seen);
+	}
+
+	return seen;
+}
+
 /*
  * Magic pathspec
  *
diff --git a/pathspec.h b/pathspec.h
index 0feb8e9f67..5b4c6614bf 100644
--- a/pathspec.h
+++ b/pathspec.h
@@ -160,6 +160,14 @@ void add_pathspec_matches_against_index(const struct pathspec *pathspec,
 char *find_pathspecs_matching_against_index(const struct pathspec *pathspec,
 					    const struct index_state *istate,
 					    enum ps_skip_worktree_action sw_action);
+char *find_pathspecs_matching_skip_worktree(const struct pathspec *pathspec);
+static inline int matches_skip_worktree(const struct pathspec *pathspec,
+					int item, char **seen_ptr)
+{
+	if (!*seen_ptr)
+		*seen_ptr = find_pathspecs_matching_skip_worktree(pathspec);
+	return (*seen_ptr)[item];
+}
 int match_pathspec_attrs(const struct index_state *istate,
 			 const char *name, int namelen,
 			 const struct pathspec_item *item);
diff --git a/t/t3705-add-sparse-checkout.sh b/t/t3705-add-sparse-checkout.sh
index 00b10ac877..2b1fd0d0ee 100755
--- a/t/t3705-add-sparse-checkout.sh
+++ b/t/t3705-add-sparse-checkout.sh
@@ -36,10 +36,26 @@ setup_gitignore () {
 	EOF
 }
 
+test_expect_success 'setup' "
+	cat >sparse_error_header <<-EOF &&
+	The following pathspecs didn't match any eligible path, but they do match index
+	entries outside the current sparse checkout:
+	EOF
+
+	cat >sparse_hint <<-EOF &&
+	hint: Disable or modify the sparsity rules if you intend to update such entries.
+	hint: Disable this message with \"git config advice.updateSparsePath false\"
+	EOF
+
+	echo sparse_entry | cat sparse_error_header - >sparse_entry_error &&
+	cat sparse_entry_error sparse_hint >error_and_hint
+"
+
 test_expect_success 'git add does not remove sparse entries' '
 	setup_sparse_entry &&
 	rm sparse_entry &&
-	git add sparse_entry &&
+	test_must_fail git add sparse_entry 2>stderr &&
+	test_cmp error_and_hint stderr &&
 	test_sparse_entry_unchanged
 '
 
@@ -47,7 +63,8 @@ test_expect_success 'git add -A does not remove sparse entries' '
 	setup_sparse_entry &&
 	rm sparse_entry &&
 	setup_gitignore &&
-	git add -A &&
+	git add -A 2>stderr &&
+	test_must_be_empty stderr &&
 	test_sparse_entry_unchanged
 '
 
@@ -55,7 +72,13 @@ test_expect_success 'git add . does not remove sparse entries' '
 	setup_sparse_entry &&
 	rm sparse_entry &&
 	setup_gitignore &&
-	git add . &&
+	test_must_fail git add . 2>stderr &&
+
+	cat sparse_error_header >expect &&
+	echo . >>expect &&
+	cat sparse_hint >>expect &&
+
+	test_cmp expect stderr &&
 	test_sparse_entry_unchanged
 '
 
@@ -64,7 +87,8 @@ do
 	test_expect_success "git add${opt:+ $opt} does not update sparse entries" '
 		setup_sparse_entry &&
 		echo modified >sparse_entry &&
-		git add $opt sparse_entry &&
+		test_must_fail git add $opt sparse_entry 2>stderr &&
+		test_cmp error_and_hint stderr &&
 		test_sparse_entry_unchanged
 	'
 done
@@ -73,14 +97,16 @@ test_expect_success 'git add --refresh does not update sparse entries' '
 	setup_sparse_entry &&
 	git ls-files --debug sparse_entry | grep mtime >before &&
 	test-tool chmtime -60 sparse_entry &&
-	git add --refresh sparse_entry &&
+	test_must_fail git add --refresh sparse_entry 2>stderr &&
+	test_cmp error_and_hint stderr &&
 	git ls-files --debug sparse_entry | grep mtime >after &&
 	test_cmp before after
 '
 
 test_expect_success 'git add --chmod does not update sparse entries' '
 	setup_sparse_entry &&
-	git add --chmod=+x sparse_entry &&
+	test_must_fail git add --chmod=+x sparse_entry 2>stderr &&
+	test_cmp error_and_hint stderr &&
 	test_sparse_entry_unchanged &&
 	! test -x sparse_entry
 '
@@ -89,8 +115,41 @@ test_expect_success 'git add --renormalize does not update sparse entries' '
 	test_config core.autocrlf false &&
 	setup_sparse_entry "LINEONE\r\nLINETWO\r\n" &&
 	echo "sparse_entry text=auto" >.gitattributes &&
-	git add --renormalize sparse_entry &&
+	test_must_fail git add --renormalize sparse_entry 2>stderr &&
+	test_cmp error_and_hint stderr &&
+	test_sparse_entry_unchanged
+'
+
+test_expect_success 'git add --dry-run --ignore-missing warn on sparse path' '
+	setup_sparse_entry &&
+	rm sparse_entry &&
+	test_must_fail git add --dry-run --ignore-missing sparse_entry 2>stderr &&
+	test_cmp error_and_hint stderr &&
 	test_sparse_entry_unchanged
 '
 
+test_expect_success 'do not advice about sparse entries when they do not match the pathspec' '
+	setup_sparse_entry &&
+	test_must_fail git add nonexistent 2>stderr &&
+	grep "fatal: pathspec .nonexistent. did not match any files" stderr &&
+	! grep -F -f sparse_error_header stderr
+'
+
+test_expect_success 'do not warn when pathspec matches dense entries' '
+	setup_sparse_entry &&
+	echo modified >sparse_entry &&
+	>dense_entry &&
+	git add "*_entry" 2>stderr &&
+	test_must_be_empty stderr &&
+	test_sparse_entry_unchanged &&
+	git ls-files --error-unmatch dense_entry
+'
+
+test_expect_success 'add obeys advice.updateSparsePath' '
+	setup_sparse_entry &&
+	test_must_fail git -c advice.updateSparsePath=false add sparse_entry 2>stderr &&
+	test_cmp sparse_entry_error stderr
+
+'
+
 test_done
-- 
2.30.1