Re: [PATCH] submodule.sh update --remote: default to oid instead of master

[Jonathan Nieder]

Stefan Beller wrote:
> On Wed, Sep 5, 2018 at 4:10 PM Jonathan Nieder  wrote:

>> Broader comment: do you think people will be surprised by this new
>> behavior?  Is there anything special we'd need to do to call it out
>> (e.g., print a warning or put something in release notes)?
>
> I guess. Not sure how to approach this best. Maybe we can
> extend the output of 'submodule update' to print that branch names
> instead of hashes for the configured case and keep printing hashes
> only for this case. Although that would not help someone who relies
> on the default solely.

Thinking more out loud: often the simplest migration path involves
multiple steps:

 1. Warn in the case that is going to change, with no behavior change
yet.

 2. Treat the case that will change as an error.  This should
help flush out cases where people were relying on the old behavior.

 3. Introduce the new behavior.  Warn that old versions of Git don't
support it yet.

 4. Eliminate the warning.  You're all clear now.

Sometimes some of these steps can be combined.

Another possible approach is to measure.  For example, is there some
way to find out how many people are relying in this "git submodule
update --remote" defaulting behavior?  One example of this approach is
to make the change (all in one step) in "next" and deploy to some
relevant subpopulation and see if anyone screams.  By making the
change in "next" instead of something with more stability guarantees,
you get the ability to roll back quickly.

There are other tools at our disposal --- e.g. command-line flags,
config, other kinds of research.

Here my first instinct would be to say this should be a command-line
flag.  To start out, we can keep the historical behavior as a default,
but introduce a command-line option for the new behavior.  This way,
people can pass the negation of that command-line option if they want
the older behavior, throughout the transition.

For example (please ignore names):

 Step 0: introduce

git submodule update --remote --default-to-master; # current behavior
git submodule update --remote --no-default-to-master; # new behavior

 and treat plain "git submodule update --remote" as --default-to-master.

 Step 1: when neither --default-to-master nor --no-default-to-master
 has been passed, warn when encountering a submodule with no branch
 and treat it as "master".

 Step 2: when neither --default-to-master nor --no-default-to-master
 has been passed, error out when encountering a submodule with no
 branch.

 Step 3: when neither --default-to-master nor --no-default-to-master
 has been passed, warn when encountering a submodule with no branch
 and treat it as pinned.

 Step 4: eliminate the warning.

What do you think?

Thanks,
Jonathan

Re: [PATCH] submodule.sh update --remote: default to oid instead of master

[Stefan Beller]

On Wed, Sep 5, 2018 at 4:10 PM Jonathan Nieder  wrote:
>
> Stefan Beller wrote:
>
> > Subject: submodule.sh update --remote: default to oid instead of master
>
> Yay!
>
> Nit: it wasn't clear to me at first what default this subject line was
> referring to.  Perhaps:
>
> submodule update --remote: skip GITLINK update when no branch is set
>
> [...]
> > --- a/Documentation/gitmodules.txt
> > +++ b/Documentation/gitmodules.txt
> > @@ -50,11 +50,12 @@ submodule..update::
> >
> >  submodule..branch::
> [...]
> > + If the option is not specified, do not update to any branch but
> > + the object id of the remote.
>
> Likewise: how about something like
>
> If not set, the default is for `git submodule update --remote`
> to update the submodule to the superproject's recorded SHA-1.

... recorded object id.

sounds good.

> > + git add .gitmodules &&
> > + git commit --allow-empty -m "submodules: pin in superproject 
> > branch"
> > + ) &&
>
> I wonder if we can do simpler by using -C + some helpers: something like
>
> git config --unset -f super/.gitmodules ... &&
> test_commit -C submodule ... &&
> git -C super submodule update ... &&
> test_cmp_rev ...
>
> Unfortunately test_cmp_rev doesn't accept a -C argument.

and the lack of fortune goes further, as test_cmp_rev needs to have
2 revisions in the same repository, i.e. both need to exist,
which is not the case.

> Broader comment: do you think people will be surprised by this new
> behavior?  Is there anything special we'd need to do to call it out
> (e.g., print a warning or put something in release notes)?

I guess. Not sure how to approach this best. Maybe we can
extend the output of 'submodule update' to print that branch names
instead of hashes for the configured case and keep printing hashes
only for this case. Although that would not help someone who relies
on the default solely.

Re: [PATCH] submodule.sh update --remote: default to oid instead of master

[Jonathan Nieder]

Stefan Beller wrote:

> Subject: submodule.sh update --remote: default to oid instead of master

Yay!

Nit: it wasn't clear to me at first what default this subject line was
referring to.  Perhaps:

submodule update --remote: skip GITLINK update when no branch is set

[...]
> --- a/Documentation/gitmodules.txt
> +++ b/Documentation/gitmodules.txt
> @@ -50,11 +50,12 @@ submodule..update::
>  
>  submodule..branch::
[...]
> + If the option is not specified, do not update to any branch but
> + the object id of the remote.

Likewise: how about something like

If not set, the default is for `git submodule update --remote`
to update the submodule to the superproject's recorded SHA-1.

[...]
> --- a/git-submodule.sh
> +++ b/git-submodule.sh
> @@ -568,16 +568,19 @@ cmd_update()
>   if test -n "$remote"
>   then
>   branch=$(git submodule--helper remote-branch "$sm_path")
> - if test -z "$nofetch"
> + if test -n "$branch"
>   then
> - # Fetch remote before determining tracking $sha1
> - fetch_in_submodule "$sm_path" $depth ||
> - die "$(eval_gettext "Unable to fetch in 
> submodule path '\$sm_path'")"
> + if test -z "$nofetch"
> + then
> + # Fetch remote before determining 
> tracking $sha1
> + fetch_in_submodule "$sm_path" $depth ||

Makes sense.  If $sha1 isn't available in the submodule, it will fetch
again later.

[...]
> --- a/t/t7406-submodule-update.sh
> +++ b/t/t7406-submodule-update.sh
> @@ -260,6 +260,28 @@ test_expect_success 'submodule update --remote should 
> fetch upstream changes wit
>   )
>  '
>  
> +test_expect_success 'submodule update --remote should not fetch upstream 
> when no branch is set' '
> + (
> + cd super &&
> + test_might_fail git config --unset -f .gitmodules 
> submodule."submodule".branch &&

Not about this patch: the quoting here is strange.

> + git add .gitmodules &&
> + git commit --allow-empty -m "submodules: pin in superproject 
> branch"
> + ) &&

I wonder if we can do simpler by using -C + some helpers: something like

git config --unset -f super/.gitmodules ... &&
test_commit -C submodule ... &&
git -C super submodule update ... &&
test_cmp_rev ...

Unfortunately test_cmp_rev doesn't accept a -C argument.

Broader comment: do you think people will be surprised by this new
behavior?  Is there anything special we'd need to do to call it out
(e.g., print a warning or put something in release notes)?

Thanks,
Jonathan

[PATCH] submodule.sh update --remote: default to oid instead of master

[Stefan Beller]

gitmodules(5) sayeth:

   submodule..branch
   A remote branch name for tracking updates in the upstream
   submodule. If the option is not specified, it defaults to master.

This doesn't allow having a "pinned" submodule that should not be updated
from upstream. We should change this to have no default --- if branch is
not specified, don't update that submodule, just like in Gerrit's
corresponding feature[1].

[1] 
https://gerrit-review.googlesource.com/Documentation/user-submodules.html#_defining_the_submodule_branch

Signed-off-by: Stefan Beller 
---
 Documentation/gitmodules.txt | 11 ++-
 git-submodule.sh | 19 +++
 t/t7406-submodule-update.sh  | 22 ++
 3 files changed, 39 insertions(+), 13 deletions(-)

diff --git a/Documentation/gitmodules.txt b/Documentation/gitmodules.txt
index 4d63def2069..3b8739f8294 100644
--- a/Documentation/gitmodules.txt
+++ b/Documentation/gitmodules.txt
@@ -50,11 +50,12 @@ submodule..update::
 
 submodule..branch::
A remote branch name for tracking updates in the upstream submodule.
-   If the option is not specified, it defaults to 'master'.  A special
-   value of `.` is used to indicate that the name of the branch in the
-   submodule should be the same name as the current branch in the
-   current repository.  See the `--remote` documentation in
-   linkgit:git-submodule[1] for details.
+   A special value of `.` is used to indicate that the name of the
+   branch in the submodule should be the same name as the current
+   branch in the current repository.  See the `--remote` documentation
+   in linkgit:git-submodule[1] for details.
+   If the option is not specified, do not update to any branch but
+   the object id of the remote.
 
 submodule..fetchRecurseSubmodules::
This option can be used to control recursive fetching of this
diff --git a/git-submodule.sh b/git-submodule.sh
index f7fd80345cd..342050ae934 100755
--- a/git-submodule.sh
+++ b/git-submodule.sh
@@ -568,16 +568,19 @@ cmd_update()
if test -n "$remote"
then
branch=$(git submodule--helper remote-branch "$sm_path")
-   if test -z "$nofetch"
+   if test -n "$branch"
then
-   # Fetch remote before determining tracking $sha1
-   fetch_in_submodule "$sm_path" $depth ||
-   die "$(eval_gettext "Unable to fetch in 
submodule path '\$sm_path'")"
+   if test -z "$nofetch"
+   then
+   # Fetch remote before determining 
tracking $sha1
+   fetch_in_submodule "$sm_path" $depth ||
+   die "$(eval_gettext "Unable to fetch in 
submodule path '\$sm_path'")"
+   fi
+   remote_name=$(sanitize_submodule_env; cd 
"$sm_path" && get_default_remote)
+   sha1=$(sanitize_submodule_env; cd "$sm_path" &&
+   git rev-parse --verify 
"${remote_name}/${branch}") ||
+   die "$(eval_gettext "Unable to find current 
\${remote_name}/\${branch} revision in submodule path '\$sm_path'")"
fi
-   remote_name=$(sanitize_submodule_env; cd "$sm_path" && 
get_default_remote)
-   sha1=$(sanitize_submodule_env; cd "$sm_path" &&
-   git rev-parse --verify 
"${remote_name}/${branch}") ||
-   die "$(eval_gettext "Unable to find current 
\${remote_name}/\${branch} revision in submodule path '\$sm_path'")"
fi
 
if ! $(git config -f "$(git rev-parse 
--git-common-dir)/modules/$name/config" core.worktree) 2>/dev/null
diff --git a/t/t7406-submodule-update.sh b/t/t7406-submodule-update.sh
index 10dc91620a6..f04884743fd 100755
--- a/t/t7406-submodule-update.sh
+++ b/t/t7406-submodule-update.sh
@@ -260,6 +260,28 @@ test_expect_success 'submodule update --remote should 
fetch upstream changes wit
)
 '
 
+test_expect_success 'submodule update --remote should not fetch upstream when 
no branch is set' '
+   (
+   cd super &&
+   test_might_fail git config --unset -f .gitmodules 
submodule."submodule".branch &&
+   git add .gitmodules &&
+   git commit --allow-empty -m "submodules: pin in superproject 
branch"
+   ) &&
+   (
+   cd submodule &&
+   echo line4b >>file &&
+   git add file &&
+   test_tick &&
+   git commit -m "upstream line4b"
+   ) &&
+   (
+   cd super &&
+   git submodule update --remote --force submodule &&
+