push: hint to use push.default=upstream when appropriatejc/advise-push-default

If you push into a shared repository that others push to, and you have
local branches in your repository that matches the remote side but do not
keep them up-to-date, then 'matching refs' is not an appropriate default
for you.

Detect when push failed due to non-fast-forward _and_ we did matching refs
by default (i.e. if the user explicitly said ':' from the command line, or
had push.default set to 'matching', then we do not want to advise), and
give a hint to tell the user that the user may want to set 'push.default'
configuration variable to 'upstream', if the remote repository receives
pushes from other places.

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

6 files changed, 37 insertions, 2 deletions

diff --git a/Documentation/config.txt b/Documentation/config.txt
index f22d926777..681811095c 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -141,6 +141,12 @@ advice.*::
 		Advice shown when you used linkgit:git-checkout[1] to
 		move to the detach HEAD state, to instruct how to create
 		a local branch after the fact.
+	pushUseUpstream::
+		Advice to set 'push.default' to 'upstream' when you ran
+		linkgit:git-push[1] and pushed 'matching refs' by default
+		(i.e. you did not have any explicit refspec on the command
+		line, and no 'push.default' configuration was set) and it
+		resulted in a non-fast-forward error.
 --
 
 core.fileMode::
diff --git a/advice.c b/advice.c
index e02e632df3..9b56709d2c 100644
--- a/advice.c
+++ b/advice.c
@@ -6,6 +6,7 @@ int advice_commit_before_merge = 1;
 int advice_resolve_conflict = 1;
 int advice_implicit_identity = 1;
 int advice_detached_head = 1;
+int advice_push_use_upstream = 1;
 
 static struct {
 	const char *name;
@@ -17,6 +18,7 @@ static struct {
 	{ "resolveconflict", &advice_resolve_conflict },
 	{ "implicitidentity", &advice_implicit_identity },
 	{ "detachedhead", &advice_detached_head },
+	{ "pushuseupstream", &advice_push_use_upstream },
 };
 
 void advise(const char *advice, ...)
diff --git a/advice.h b/advice.h
index e5d0af782b..6bb89cdce0 100644
--- a/advice.h
+++ b/advice.h
@@ -9,6 +9,7 @@ extern int advice_commit_before_merge;
 extern int advice_resolve_conflict;
 extern int advice_implicit_identity;
 extern int advice_detached_head;
+extern int advice_push_use_upstream;
 
 int git_default_advice_config(const char *var, const char *value);
 void advise(const char *advice, ...);
diff --git a/builtin/push.c b/builtin/push.c
index 35cce532f2..5f8c7f4917 100644
--- a/builtin/push.c
+++ b/builtin/push.c
@@ -9,6 +9,7 @@
 #include "transport.h"
 #include "parse-options.h"
 #include "submodule.h"
+#include "advice.h"
 
 static const char * const push_usage[] = {
 	"git push [<options>] [<repository> [<refspec>...]]",
@@ -24,6 +25,7 @@ static int progress;
 static const char **refspec;
 static int refspec_nr;
 static int refspec_alloc;
+static int default_matching_used;
 
 static void add_refspec(const char *ref)
 {
@@ -95,6 +97,9 @@ static void setup_default_push_refspecs(struct remote *remote)
 {
 	switch (push_default) {
 	default:
+	case PUSH_DEFAULT_UNSPECIFIED:
+		default_matching_used = 1;
+		/* fallthru */
 	case PUSH_DEFAULT_MATCHING:
 		add_refspec(":");
 		break;
@@ -114,6 +119,23 @@ static void setup_default_push_refspecs(struct remote *remote)
 	}
 }
 
+static const char *message_advice_use_upstream[] = {
+	"If you are pushing into a repository that receives pushes from",
+	"repositories other than the current repository, you may want to",
+	"set 'push.default' configuration variable to 'upstream' to avoid",
+	"pushing branches you haven't worked on that others have updated.",
+};
+
+static void advise_use_upstream(void)
+{
+	int i;
+
+	if (!advice_push_use_upstream)
+		return;
+	for (i = 0; i < ARRAY_SIZE(message_advice_use_upstream); i++)
+		advise(message_advice_use_upstream[i]);
+}
+
 static int push_with_options(struct transport *transport, int flags)
 {
 	int err;
@@ -136,6 +158,9 @@ static int push_with_options(struct transport *transport, int flags)
 
 	err |= transport_disconnect(transport);
 
+	if (nonfastforward && default_matching_used)
+		advise_use_upstream();
+
 	if (!err)
 		return 0;
 
diff --git a/cache.h b/cache.h
index 2e6ad3604e..d5351fa566 100644
--- a/cache.h
+++ b/cache.h
@@ -623,7 +623,8 @@ enum push_default_type {
 	PUSH_DEFAULT_NOTHING = 0,
 	PUSH_DEFAULT_MATCHING,
 	PUSH_DEFAULT_UPSTREAM,
-	PUSH_DEFAULT_CURRENT
+	PUSH_DEFAULT_CURRENT,
+	PUSH_DEFAULT_UNSPECIFIED
 };
 
 extern enum branch_track git_branch_track;
diff --git a/environment.c b/environment.c
index 0bee6a7a88..e5fb862a9b 100644
--- a/environment.c
+++ b/environment.c
@@ -51,7 +51,7 @@ enum safe_crlf safe_crlf = SAFE_CRLF_WARN;
 unsigned whitespace_rule_cfg = WS_DEFAULT_RULE;
 enum branch_track git_branch_track = BRANCH_TRACK_REMOTE;
 enum rebase_setup_type autorebase = AUTOREBASE_NEVER;
-enum push_default_type push_default = PUSH_DEFAULT_MATCHING;
+enum push_default_type push_default = PUSH_DEFAULT_UNSPECIFIED;
 #ifndef OBJECT_CREATION_MODE
 #define OBJECT_CREATION_MODE OBJECT_CREATION_USES_HARDLINKS
 #endif