add: warn when -u or -A is used without pathspec

Most Git commands that can be used with or without pathspec operate
tree-wide by default, the pathspec being used to restrict their
scope.  A few exceptions are: 'git grep', 'git clean', 'git add -u'
and 'git add -A'.  When run in a subdirectory without pathspec, they
operate only on paths in the current directory.

The inconsistency of 'git add -u' and 'git add -A' is particularly
problematic since other 'git add' subcommands (namely 'git add -p'
and 'git add -e') are tree-wide by default.  It also means that "git
add -u && git commit" will record a state that is different from
what is recorded with "git commit -a".

Flipping the default now is unacceptable, so let's start training
users to type 'git add -u|-A :/' or 'git add -u|-A .' explicitly, to
prepare for the next steps:

* forbid 'git add -u|-A' without pathspec (like 'git add' without
  option)

* much later, maybe, re-allow 'git add -u|-A' without pathspec, that
  will add all tracked and modified files, or all files, tree-wide.

A nice side effect of this patch is that it makes the :/ magic
pathspec easier to discover for users.

When the command is called from the root of the tree, there is no
ambiguity and no need to change the behavior, hence no need to warn.

Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-add.txt

@@ -107,9 +107,10 @@ apply to the index. See EDITING PATCHES below.
 	from the index if the corresponding files in the working tree
 	have been removed.
 +
-If no <filepattern> is given, default to "."; in other words,
-update all tracked files in the current directory and its
-subdirectories.
+If no <filepattern> is given, the current version of Git defaults to
+"."; in other words, update all tracked files in the current directory
+and its subdirectories. This default will change in a future version
+of Git, hence the form without <filepattern> should not be used.
 
 -A::
 --all::

builtin/add.c

@@ -363,6 +363,35 @@ static int add_files(struct dir_struct *dir, int flags)
 	return exit_status;
 }
 
+static void warn_pathless_add(const char *option_name, const char *short_name) {
+	/*
+	 * To be consistent with "git add -p" and most Git
+	 * commands, we should default to being tree-wide, but
+	 * this is not the original behavior and can't be
+	 * changed until users trained themselves not to type
+	 * "git add -u" or "git add -A". For now, we warn and
+	 * keep the old behavior. Later, this warning can be
+	 * turned into a die(...), and eventually we may
+	 * reallow the command with a new behavior.
+	 */
+	warning(_("The behavior of 'git add %s (or %s)' with no path argument from a\n"
+		  "subdirectory of the tree will change in Git 2.0 and should not be used anymore.\n"
+		  "To add content for the whole tree, run:\n"
+		  "\n"
+		  "  git add %s :/\n"
+		  "  (or git add %s :/)\n"
+		  "\n"
+		  "To restrict the command to the current directory, run:\n"
+		  "\n"
+		  "  git add %s .\n"
+		  "  (or git add %s .)\n"
+		  "\n"
+		  "With the current Git version, the command is restricted to the current directory."),
+		option_name, short_name,
+		option_name, short_name,
+		option_name, short_name);
+}
+
 int cmd_add(int argc, const char **argv, const char *prefix)
 {
 	int exit_status = 0;
@@ -373,6 +402,8 @@ int cmd_add(int argc, const char **argv, const char *prefix)
 	int add_new_files;
 	int require_pathspec;
 	char *seen = NULL;
+	const char *option_with_implicit_dot = NULL;
+	const char *short_option_with_implicit_dot = NULL;
 
 	git_config(add_config, NULL);
 
@@ -392,8 +423,19 @@ int cmd_add(int argc, const char **argv, const char *prefix)
 		die(_("-A and -u are mutually incompatible"));
 	if (!show_only && ignore_missing)
 		die(_("Option --ignore-missing can only be used together with --dry-run"));
-	if ((addremove || take_worktree_changes) && !argc) {
+	if (addremove) {
+		option_with_implicit_dot = "--all";
+		short_option_with_implicit_dot = "-A";
+	}
+	if (take_worktree_changes) {
+		option_with_implicit_dot = "--update";
+		short_option_with_implicit_dot = "-u";
+	}
+	if (option_with_implicit_dot && !argc) {
 		static const char *here[2] = { ".", NULL };
+		if (prefix)
+			warn_pathless_add(option_with_implicit_dot,
+					  short_option_with_implicit_dot);
 		argc = 1;
 		argv = here;
 	}