[PATCHv3 1/2] 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 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.

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>
---

Jeff,
thanks for the suggestions, both git_path(..) as well as checking the config,
this seems quite readable to me:

 builtin/push.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/builtin/push.c b/builtin/push.c
index 3bb9d6b..65bb1df 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;
 static int recurse_submodules = RECURSE_SUBMODULES_DEFAULT;
 static enum transport_family family;
 
@@ -31,6 +33,14 @@ static const char **refspec;
 static int refspec_nr;
 static int refspec_alloc;
 
+static void preset_submodule_default(void)
+{
+	if (has_submodules || file_exists(git_path("modules")))
+		recurse_submodules = RECURSE_SUBMODULES_CHECK;
+	else
+		recurse_submodules = RECURSE_SUBMODULES_OFF;
+}
+
 static void add_refspec(const char *ref)
 {
 	refspec_nr++;
@@ -495,7 +505,8 @@ 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"))
+		has_submodules = 1;
 
 	return git_default_config(k, v, NULL);
 }
@@ -552,6 +563,7 @@ 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);
-- 
2.10.0.129.g35f6318