receive-pack: explain what to do when push updates the current branch

This makes "git push" issue a more detailed instruction when a user pushes
into the current branch of a non-bare repository without having an
explicit configuration set to receive.denycurrentbranch.  In such a case,
it will also tell the user that the default will change to refusal in a
future version of git.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-receive-pack.c

@@ -12,14 +12,15 @@
 static const char receive_pack_usage[] = "git-receive-pack <git-dir>";
 
 enum deny_action {
+	DENY_UNCONFIGURED,
 	DENY_IGNORE,
 	DENY_WARN,
 	DENY_REFUSE,
 };
 
 static int deny_deletes = 0;
 static int deny_non_fast_forwards = 0;
-static enum deny_action deny_current_branch = DENY_WARN;
+static enum deny_action deny_current_branch = DENY_UNCONFIGURED;
 static int receive_fsck_objects;
 static int receive_unpack_limit = -1;
 static int transfer_unpack_limit = -1;
@@ -214,6 +215,35 @@ static int is_ref_checked_out(const char *ref)
 	return !strcmp(head, ref);
 }
 
+static char *warn_unconfigured_deny_msg[] = {
+	"Updating the currently checked out branch may cause confusion,",
+	"as the index and work tree do not reflect changes that are in HEAD.",
+	"As a result, you may see the changes you just pushed into it",
+	"reverted when you run 'git diff' over there, and you may want",
+	"to run 'git reset --hard' before starting to work to recover.",
+	"",
+	"You can set 'receive.denyCurrentBranch' configuration variable to",
+	"'refuse' in the remote repository to forbid pushing into its",
+	"current branch."
+	"",
+	"To allow pushing into the current branch, you can set it to 'ignore';",
+	"but this is not recommended unless you arranged to update its work",
+	"tree to match what you pushed in some other way.",
+	"",
+	"To squelch this message, you can set it to 'warn'.",
+	"",
+	"Note that the default will change in a future version of git",
+	"to refuse updating the current branch unless you have the",
+	"configuration variable set to either 'ignore' or 'warn'."
+};
+
+static void warn_unconfigured_deny(void)
+{
+	int i;
+	for (i = 0; i < ARRAY_SIZE(warn_unconfigured_deny_msg); i++)
+		warning(warn_unconfigured_deny_msg[i]);
+}
+
 static const char *update(struct command *cmd)
 {
 	const char *name = cmd->ref_name;
@@ -227,22 +257,20 @@ static const char *update(struct command *cmd)
 		return "funny refname";
 	}
 
-	switch (deny_current_branch) {
-	case DENY_IGNORE:
-		break;
-	case DENY_WARN:
-		if (!is_ref_checked_out(name))
+	if (is_ref_checked_out(name)) {
+		switch (deny_current_branch) {
+		case DENY_IGNORE:
 			break;
-		warning("updating the currently checked out branch; this may"
-			" cause confusion,\n"
-			"as the index and working tree do not reflect changes"
-			" that are now in HEAD.");
-		break;
-	case DENY_REFUSE:
-		if (!is_ref_checked_out(name))
+		case DENY_UNCONFIGURED:
+		case DENY_WARN:
+			warning("updating the current branch");
+			if (deny_current_branch == DENY_UNCONFIGURED)
+				warn_unconfigured_deny();
 			break;
-		error("refusing to update checked out branch: %s", name);
-		return "branch is currently checked out";
+		case DENY_REFUSE:
+			error("refusing to update checked out branch: %s", name);
+			return "branch is currently checked out";
+		}
 	}
 
 	if (!is_null_sha1(new_sha1) && !has_sha1_file(new_sha1)) {

t/t5516-fetch-push.sh

@@ -492,7 +492,7 @@ test_expect_success 'warn on push to HEAD of non-bare repository' '
 		git checkout master &&
 		git config receive.denyCurrentBranch warn) &&
 	git push testrepo master 2>stderr &&
-	grep "warning.*this may cause confusion" stderr
+	grep "warning: updating the current branch" stderr
 '
 
 test_expect_success 'deny push to HEAD of non-bare repository' '
@@ -510,7 +510,7 @@ test_expect_success 'allow push to HEAD of bare repository (bare)' '
 		git config receive.denyCurrentBranch true &&
 		git config core.bare true) &&
 	git push testrepo master 2>stderr &&
-	! grep "warning.*this may cause confusion" stderr
+	! grep "warning: updating the current branch" stderr
 '
 
 test_expect_success 'allow push to HEAD of non-bare repository (config)' '
@@ -520,7 +520,7 @@ test_expect_success 'allow push to HEAD of non-bare repository (config)' '
 		git config receive.denyCurrentBranch false
 	) &&
 	git push testrepo master 2>stderr &&
-	! grep "warning.*this may cause confusion" stderr
+	! grep "warning: updating the current branch" stderr
 '
 
 test_expect_success 'fetch with branches' '