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Re: Test::Smoke failing to test most recent commit to Perl 5 blead

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From:
demerphq
Date:
January 28, 2017 03:58
Subject:
Re: Test::Smoke failing to test most recent commit to Perl 5 blead
Message ID:
CANgJU+UnkepMS3G_8uFfu3eYXg+u5D2w-t7CGJxjpteBM9yPJQ@mail.gmail.com
On 28 Jan 2017 6:32 a.m., "James E Keenan" <jkeen@verizon.net> wrote:

> On 01/14/2017 10:10 AM, James E Keenan wrote:
> Here is the first part of the smokecurrent.log for this run -- with some
> comments:
>
> #####
> [2017-01-27 08:11:22-0500] Read configuration from:
> /usr/home/jkeenan/p5smoke/install/smokecurrent_config
> [2017-01-27 08:11:22-0500] Commitlevel before sync:
> d6115793d6cc41755a3ed4baaa38d30653656f41
>
> # d611579 was HEAD in the previous branch being smoked:
> smoke-me/jkeenan/130635-storable
>
> [2017-01-27 08:11:22-0500] ==> Starting synctree
> [2017-01-27 08:11:22-0500] Reading branch to smoke from:
> '/usr/home/jkeenan/p5smoke/install/smokecurrent.gitbranch'
> [2017-01-27 08:11:22-0500] In pwd(/usr/home/jkeenan/p5smoke/git-perl)
> running:
> [2017-01-27 08:11:22-0500] qx[/usr/local/bin/git pull --all]
> From git://perl5.git.perl.org/perl
>    1f74a12..9a7b7fb  blead      -> origin/blead
> [2017-01-27 08:11:37-0500] Fetching origin
> [2017-01-27 08:11:37-0500] Already up-to-date.
> [2017-01-27 08:11:37-0500] In pwd(/usr/home/jkeenan/p5smoke/git-perl)
> running:
> [2017-01-27 08:11:37-0500] qx[/usr/local/bin/git remote prune origin]
> [2017-01-27 08:11:38-0500] In pwd(/usr/home/jkeenan/p5smoke/git-perl)
> running:
> [2017-01-27 08:11:38-0500] qx[/usr/local/bin/git checkout blead
> [2017-01-27 08:11:38-0500]  2>&1]
> Switched to branch 'blead'
> [2017-01-27 08:11:41-0500] Your branch is behind 'origin/blead' by 7
> commits, and can be fast-forwarded.
> [2017-01-27 08:11:41-0500]   (use "git pull" to update your local branch)
>
> # Note: No indication that 'git pull' was actually run!  Why not?
>
> [2017-01-27 08:11:41-0500] In pwd(/usr/home/jkeenan/p5smoke/perl-current)
> running:
> [2017-01-27 08:11:41-0500] qx[/usr/local/bin/git reset --hard]
>
> # Note: Although 'man git-reset' is not explicit about this, we can
> probably assume
> # that 'git reset --hard' with no <commit> resets to HEAD -- i.e., no
> update to checkout.
>
>
Yes. It throws away any changes to the current branch. That should say

git reset --hard origin/blead


> [2017-01-27 08:11:43-0500] HEAD is now at d611579 Fix stack buffer
> overflow in deserialization of hooks.
> #####
>
> So why does Test-Smoke not update the branch being tested in cases like
> this?
>
>
This is an educated guess: whoever wrote that code did not understand git
well and got confused about what git pull does, and what git pull --all do.

Seeing git pull in a script like this is a red flag, seeing  --all is a
bigger red flag for me. ( It does not "pull all", it does a fetch against
all remotes.)

IMO git pull is not really suitable for scripting as it can trigger a
rebase or merge, and trigger an editor.

I would expect to see a sequence like this:

git remote update -p
git checkout $branch
git reset --hard origin/$branch

or like this:

git remote prune --all
git fetch --all
git checkout $branch
git reset --hard origin/$branch

or even like this:

git fetch origin
git checkout $branch
git reset --hard origin/$branch

The difference between the variants being about whether the code should be
managing multiple upstream repos or not. The --all introduces ambiguity
about this, as it means "fetch code from --all remotes", so one might guess
someone wanted to support multiple upstreams. On the other hand, my guess
is that the person who coded it to do a 'git pull --all' thought that the
-all would update --all branches, which it does not. Bolstering this view
is that it seems to make little sense to smoke branches from multiple
upstreams, especially for Perl. I would have expected only the canonical
branches in the master upstream repo should be smoked, so the --all
probably was a bug.

What appears to be happening is that when the pull is executed it is in a
different branch, so it fetches and then updates *THAT* branch only (via a
merge!). When it then checks-out the new branch branch it is on an old
commit, and requires a reset to the latest code.

I would recommend that the smoke scripts do not use pull *ever*. They
should never ever modify code, so doing a pull makes no sense.  git pull is
basically a smart wrapper around git fetch + git merge. A smoker should
*NEVER* be doing git-merge, so it should *never* be using git-pull.

Note, I am fully aware that under perfect circumstances you /can/ script
this using git pull. I would recommend not to. First it is confusing.
Second, if circumstances are less than perfect then it could lead to
unwanted behavior. For instance someone tinkers in a branch used by the
smoker, then one could imaging the script breaking because of uncommitted
changes, or breaking because pull has triggered a merge which requires a
edited text message.

FWIW, i have in the past recommended that new users to git do NOT use "git
pull", until they have mastered using "git fetch" and "git rebase" or "git
merge" as independent commands. Only once having experience of the three
basic commands should people use git pull. Since it is a wrapper around
three distinct commands it easily leads to confusion in the inexperienced.

yves

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