[RFC/PATCH] add: warn when -u or -A is used without filepattern

[Matthieu Moy <Matthieu.Moy@imag.fr>]

Most git commands that can be used with our without a filepattern are
tree-wide by default, the filepattern being used to restrict their scope.
A few exceptions are: 'git grep', 'git clean', 'git add -u' and 'git add -A'.

The inconsistancy of 'git add -u' and 'git add -A' are particularly
problematic since other 'git add' subcommands (namely 'git add -p' and
'git add -e') are tree-wide by default.

Flipping the default now is unacceptable, so this patch starts training
users to type explicitely 'git add -u|-A :/' or 'git add -u|-A .', to prepare
for the next steps:

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

* much later, maybe, re-allow 'git add -u|-A' without filepattern, with a
  tree-wide scope.

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

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

> The first step of "git add -u" migration plan would be to warn when
> no argument is given and update all the existing index entries, and
> give the same advise to use either "." or ":/".  Keep this for three
> cycles: 3 * (8 to 10 weeks per cycle) = 27 weeks ~ 1/2 year.

The first step should look like this patch. The message remains vague
about the next steps ("change in a future Git version", no mention of
the exact change nor of the exact version in which it will happen),
but I'm fine with refining it (perhaps this could be a 2.0 change,
like the change to push.default?).

 Documentation/git-add.txt |  7 ++++---
 builtin/add.c             | 30 +++++++++++++++++++++++++++++-
 2 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/Documentation/git-add.txt b/Documentation/git-add.txt
index fd9e36b..5333559 100644
--- a/Documentation/git-add.txt
+++ b/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::
diff --git a/builtin/add.c b/builtin/add.c
index e664100..e6eb829 100644
--- a/builtin/add.c
+++ b/builtin/add.c
@@ -373,6 +373,7 @@ 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;
 
 	git_config(add_config, NULL);
 
@@ -392,7 +393,34 @@ 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";
+	if (take_worktree_changes)
+		option_with_implicit_dot = "--update";
+	if (option_with_implicit_dot && !argc) {
+		/*
+		 * To be consistant 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' with no path argument will change in a future\n"
+			  "Git version and shouldn't be used anymore.  To add content for the whole tree, run:\n"
+			  "\n"
+			  "  git add %s :/\n"
+			  "\n"
+			  "To restrict the command to the current directory, run:\n"
+			  "\n"
+			  "  git add %s .\n"
+			  "\n"
+			  "With the current Git version, the command is restricted to the current directory."),
+			option_with_implicit_dot,
+			option_with_implicit_dot,
+			option_with_implicit_dot);
 		static const char *here[2] = { ".", NULL };
 		argc = 1;
 		argv = here;
-- 
1.8.0.319.g8abfee4