Subject: Re: 'simple' push check that branch name matches does not work if push.default is unset (and hence implicitly simple)

From: Jeff King <[email-masked]>
Date: Wed, 26 Nov 2014 22:43:06 -0500

On Wed, Nov 26, 2014 at 02:29:28PM -0800, Adam Williamson wrote:

> Hi, folks. Ran into an unfortunate issue with git which helped me mess
> up a Fedora package repo today :/
> 
> The problem can be reproduced thus:
> 
> 1. Create an empty repo, clone it
> 2. Push its master branch with something in it (just to get started)
> 3. git branch --track moo origin/master
> 4. git checkout moo
> 5. echo moo >> moo && git commit -a -m "create moo"
> 6. git push
> ** BUG HAPPENS - CHANGES ARE PUSHED TO origin/master **
> 7. git config --local push.default simple
> 8. echo moo2 >> moo && git commit -a -m "update moo"
> 9. git push
> ** PUSH IS CORRECTLY REJECTED **
> 
> In both those cases, the push behaviour is supposed to be 'simple' - at
> step 6 it's *implicitly* set to 'simple' (according to the
> documentation), while at step 9 it's *explicitly* set to 'simple'. At
> step 6, a warning is printed to the console:

Ugh. Yeah, this never worked properly, even in the original v2.0.0
release. Worse, our tests did not notice it at all.  Patch is below.

-- >8 --
Subject: push: truly use "simple" as default, not "upstream"

The plan for the push.default transition had all along been
to use the "simple" method rather than "upstream" as a
default if the user did not specify their own push.default
value. Commit 11037ee (push: switch default from "matching"
to "simple", 2013-01-04) tried to implement that by moving
PUSH_DEFAULT_UNSPECIFIED in our switch statement to
fall-through to the PUSH_DEFAULT_SIMPLE case.

When the commit that became 11037ee was originally written,
that would have been enough. We would fall through to
calling setup_push_upstream() with the "simple" parameter
set to 1. However, it was delayed for a while until we were
ready to make the transition in Git 2.0.

And in the meantime, commit ed2b182 (push: change `simple`
to accommodate triangular workflows, 2013-06-19) threw a
monkey wrench into the works. That commit drops the "simple"
parameter to setup_push_upstream, and instead checks whether
the global "push_default" is PUSH_DEFAULT_SIMPLE. This is
right when the user has explicitly configured push.default
to simple, but wrong when we are a fall-through for the
"unspecified" case.

We never noticed because our push.default tests do not cover
the case of the variable being totally unset; they only
check the "simple" behavior itself.

Signed-off-by: Jeff King <[email-masked]>
---
ed2b182 comes from Ram, but the suggestion for this bit of code actually
comes from Junio in:

  http://thread.gmane.org/gmane.comp.version-control.git/228383/focus=228436

I am not sure I understand the reason for dropping the "simple"
parameter in that commit in the first place. If we are in triangular
mode, then we would not get to setup_push_upstream from "simple" (or the
default) in the first place (we would use "current" instead). The only
time "triangular" matters to setup_push_upstream is when push.default
really has been set to "upstream", but in that case, "simple" would
always be 0 (and likewise, the equality check that replaces it would
also be false).

So I have a vague concern that I'm missing something. Maybe one of you
who worked on it can recall more.

 builtin/push.c          |  8 ++++----
 t/t5528-push-default.sh | 32 ++++++++++++++++++++++++++++++--
 2 files changed, 34 insertions(+), 6 deletions(-)

diff --git a/builtin/push.c b/builtin/push.c
index a076b19..7aedf6f 100644
--- a/builtin/push.c
+++ b/builtin/push.c
@@ -161,7 +161,7 @@ static const char message_detached_head_die[] =
 	   "    git push %s HEAD:<name-of-remote-branch>\n");
 
 static void setup_push_upstream(struct remote *remote, struct branch *branch,
-				int triangular)
+				int triangular, int simple)
 {
 	struct strbuf refspec = STRBUF_INIT;
 
@@ -184,7 +184,7 @@ static void setup_push_upstream(struct remote *remote, struct branch *branch,
 		      "to update which remote branch."),
 		    remote->name, branch->name);
 
-	if (push_default == PUSH_DEFAULT_SIMPLE) {
+	if (simple) {
 		/* Additional safety */
 		if (strcmp(branch->refname, branch->merge[0]->src))
 			die_push_simple(branch, remote);
@@ -257,11 +257,11 @@ static void setup_default_push_refspecs(struct remote *remote)
 		if (triangular)
 			setup_push_current(remote, branch);
 		else
-			setup_push_upstream(remote, branch, triangular);
+			setup_push_upstream(remote, branch, triangular, 1);
 		break;
 
 	case PUSH_DEFAULT_UPSTREAM:
-		setup_push_upstream(remote, branch, triangular);
+		setup_push_upstream(remote, branch, triangular, 0);
 		break;
 
 	case PUSH_DEFAULT_CURRENT:
diff --git a/t/t5528-push-default.sh b/t/t5528-push-default.sh
index 6a5ac3a..cc74519 100755
--- a/t/t5528-push-default.sh
+++ b/t/t5528-push-default.sh
@@ -26,7 +26,7 @@ check_pushed_commit () {
 # $2 = expected target branch for the push
 # $3 = [optional] repo to check for actual output (repo1 by default)
 test_push_success () {
-	git -c push.default="$1" push &&
+	git ${1:+-c push.default="$1"} push &&
 	check_pushed_commit HEAD "$2" "$3"
 }
 
@@ -34,7 +34,7 @@ test_push_success () {
 # check that push fails and does not modify any remote branch
 test_push_failure () {
 	git --git-dir=repo1 log --no-walk --format='%h %s' --all >expect &&
-	test_must_fail git -c push.default="$1" push &&
+	test_must_fail git ${1:+-c push.default="$1"} push &&
 	git --git-dir=repo1 log --no-walk --format='%h %s' --all >actual &&
 	test_cmp expect actual
 }
@@ -172,4 +172,32 @@ test_pushdefault_workflow success simple master triangular
 # master is updated (parent2 does not have foo)
 test_pushdefault_workflow success matching master triangular
 
+# default tests, when no push-default is specified. This
+# should behave the same as "simple" in non-triangular
+# settings, and as "current" otherwise.
+
+test_expect_success 'default behavior allows "simple" push' '
+	test_config branch.master.remote parent1 &&
+	test_config branch.master.merge refs/heads/master &&
+	test_config remote.pushdefault parent1 &&
+	test_commit default-master-master &&
+	test_push_success "" master
+'
+
+test_expect_success 'default behavior rejects non-simple push' '
+	test_config branch.master.remote parent1 &&
+	test_config branch.master.merge refs/heads/foo &&
+	test_config remote.pushdefault parent1 &&
+	test_commit default-master-foo &&
+	test_push_failure ""
+'
+
+test_expect_success 'default triangular behavior acts like "current"' '
+	test_config branch.master.remote parent1 &&
+	test_config branch.master.merge refs/heads/foo &&
+	test_config remote.pushdefault parent2 &&
+	test_commit default-triangular &&
+	test_push_success "" master repo2
+'
+
 test_done
-- 
2.2.0.rc2.402.g4519813