[PATCHv5] push: change submodule default to check when submodules exist

[Stefan Beller <sbeller@google.com>]

When working with submodules, it is easy to forget to push the submodules.
The setting 'check', which checks if any existing submodule is present on
at least one remote of the submodule remotes, is designed to prevent this
mistake.

Flipping the default to check for submodules is safer than the current
default of ignoring submodules while pushing.

However checking for submodules requires additional work[1], which annoys
users that do not use submodules, so we turn on the check for submodules
based on a cheap heuristic, the existence of
* any initialized submodules via checking submodule.<name>.url.
* the .git/modules directory. That directory doesn't exist when no
  submodules are used and is only created and populated when submodules
  are cloned/added.
* the existence of the .gitmodules file.

When the submodule directory doesn't exist, a user may have changed the
gitlinks via plumbing commands. Currently the default is to not check.
RECURSE_SUBMODULES_DEFAULT is effectively RECURSE_SUBMODULES_OFF currently,
though it may change in the future. When no submodules exist such a check
is pointless as it would fail anyway, so let's just turn it off.

[1] https://public-inbox.org/git/CA+55aFyos78qODyw57V=w13Ux5-8SvBqObJFAq22K+XKPWVbAA@mail.gmail.com/

Signed-off-by: Stefan Beller <sbeller@google.com>
---

 * Reworded the commit message
 * added comment on why we only check submodule.<name>.url

 The first patch of the series is still good, so please use
 https://public-inbox.org/git/20161006193725.31553-2-sbeller@google.com/
 first and then build this on top.
 
 Thanks,
 Stefan 

 builtin/push.c                 | 16 +++++++++++++++-
 t/t5531-deep-submodule-push.sh |  6 +++++-
 2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/builtin/push.c b/builtin/push.c
index 3bb9d6b..9e0b8db 100644
--- a/builtin/push.c
+++ b/builtin/push.c
@@ -3,6 +3,7 @@
  */
 #include "cache.h"
 #include "refs.h"
+#include "dir.h"
 #include "run-command.h"
 #include "builtin.h"
 #include "remote.h"
@@ -22,6 +23,7 @@ static int deleterefs;
 static const char *receivepack;
 static int verbosity;
 static int progress = -1;
+static int has_submodules_configured;
 static int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
 static enum transport_family family;
 
@@ -31,6 +33,15 @@ static const char **refspec;
 static int refspec_nr;
 static int refspec_alloc;
 
+static void preset_submodule_default(void)
+{
+	if (has_submodules_configured || file_exists(git_path("modules")) ||
+	    (!is_bare_repository() && file_exists(".gitmodules")))
+		recurse_submodules = RECURSE_SUBMODULES_CHECK;
+	else
+		recurse_submodules = RECURSE_SUBMODULES_OFF;
+}
+
 static void add_refspec(const char *ref)
 {
 	refspec_nr++;
@@ -495,7 +506,9 @@ static int git_push_config(const char *k, const char *v, void *cb)
 		const char *value;
 		if (!git_config_get_value("push.recursesubmodules", &value))
 			recurse_submodules = parse_push_recurse_submodules_arg(k, value);
-	}
+	} else if (starts_with(k, "submodule.") && ends_with(k, ".url"))
+		/* The submodule.<name>.url is used as a bit to indicate existence */
+		has_submodules_configured = 1;
 
 	return git_default_config(k, v, NULL);
 }
@@ -552,6 +565,7 @@ int cmd_push(int argc, const char **argv, const char *prefix)
 	};
 
 	packet_trace_identity("push");
+	preset_submodule_default();
 	git_config(git_push_config, &flags);
 	argc = parse_options(argc, argv, prefix, options, push_usage, 0);
 	set_push_cert_flags(&flags, push_cert);
diff --git a/t/t5531-deep-submodule-push.sh b/t/t5531-deep-submodule-push.sh
index 198ce84..e690749 100755
--- a/t/t5531-deep-submodule-push.sh
+++ b/t/t5531-deep-submodule-push.sh
@@ -65,7 +65,11 @@ test_expect_success 'push fails if submodule commit not on remote' '
 		git add gar/bage &&
 		git commit -m "Third commit for gar/bage" &&
 		# the push should fail with --recurse-submodules=check
-		# on the command line...
+		# on the command line. "check" is the default for repos in
+		# which submodules are detected by existence of config,
+		# .gitmodules file or an internal .git/modules/<submodule-repo>
+		git submodule add -f ../submodule.git gar/bage &&
+		test_must_fail git push ../pub.git master &&
 		test_must_fail git push --recurse-submodules=check ../pub.git master &&
 
 		# ...or if specified in the configuration..
-- 
2.10.1.353.g1629400