Re: [BUG] [git 2.16.1] yeeek ... my files are gone .. by git pull <otherRepositoryUrl>

["\"Marcel 'childNo͡.de' Trautwein\"" <c0d3+gitscm@childno.de>]

> Am 23.02.2018 um 00:20 schrieb Jonathan Nieder <jrnieder@gmail.com>:
> 
> Hi Marcel,
> 
> …
> Sorry, this is not the most helpful reply but:
> 
> Can you describe a reproduction recipe so that I can experience the
> same thing?
> 
> That is:
> 
> 1. steps to reproduce
> 2. expected result
> 3. actual result
> 4. the difference and why it was unexpected
> 

1. steps to reproduce
=====================
```
Last login: Fri Feb 23 00:33:11 on ttys001
~ PATH variable not enhanced, no applications found in ~/Applications/*-latest


-bash:/Users/marcel:$ mkdir /tmp/$$
change to new directory '/tmp/2608'? [Y/n] 


-bash:/tmp/2608:$ mkdir a.git
change to new directory 'a.git'? [Y/n] 


-bash:/tmp/2608/a.git:$ git init
Initialized empty Git repository in /private/tmp/2608/a.git/.git/


-bash:/tmp/2608/a.git:$ touch foo


-bash:/tmp/2608/a.git:$ git add foo


-bash:/tmp/2608/a.git:$ git commit -m "foo" foo
[master (root-commit) ed191c4] foo
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 foo


-bash:/tmp/2608/a.git:$ cd -
/tmp/2608


-bash:/tmp/2608:$ mkdir b.git
change to new directory 'b.git'? [Y/n] 


-bash:/tmp/2608/b.git:$ git init
Initialized empty Git repository in /private/tmp/2608/b.git/.git/


-bash:/tmp/2608/b.git:$ touch bar


-bash:/tmp/2608/b.git:$ git add bar


-bash:/tmp/2608/b.git:$ git commit -m "bar" bar
[master (root-commit) 80b0355] bar
 1 file changed, 0 insertions(+), 0 deletions(-)
 create mode 100644 bar


-bash:/tmp/2608/b.git:$ cd -
/tmp/2608


-bash:/tmp/2608:$ git clone a.git c
Cloning into 'c'...
done.


-bash:/tmp/2608:$ cd c


-bash:/tmp/2608/c:$ ll
total 0
drwxr-xr-x  12 marcel  wheel   384B 23 Feb 05:47 .git
-rw-r--r--   1 marcel  wheel     0B 23 Feb 05:47 foo


-bash:/tmp/2608/c:$ git pull ../b.git/
warning: no common commits
remote: Counting objects: 3, done.
remote: Total 3 (delta 0), reused 0 (delta 0)
Unpacking objects: 100% (3/3), done.
From ../b
 * branch            HEAD       -> FETCH_HEAD
Successfully rebased and updated refs/heads/master.


-bash:/tmp/2608/c:$ ll
total 0
drwxr-xr-x  14 marcel  wheel   448B 23 Feb 05:47 .git
-rw-r--r--   1 marcel  wheel     0B 23 Feb 05:47 bar


-bash:/tmp/2608/c:$ git reflog
80b0355 (HEAD -> master) HEAD@{0}: pull ../b.git/: checkout 80b03552466bc526b1130ce5ca4a991ba31a0546: returning to refs/heads/master
80b0355 (HEAD -> master) HEAD@{1}: pull ../b.git/: checkout 80b03552466bc526b1130ce5ca4a991ba31a0546
ed191c4 (origin/master, origin/HEAD) HEAD@{2}: clone: from /tmp/2608/a.git


-bash:/tmp/2608/c:$ git remote -v
origin	/tmp/2608/a.git (fetch)
origin	/tmp/2608/a.git (push)


-bash:/tmp/2608/c:$  git log --all --graph --decorate --oneline --simplify-by-decoration
* 80b0355 (HEAD -> master) bar
* ed191c4 (origin/master, origin/HEAD) foo
```

2. expected result
==================
just an error in case the too trees have no common ancestors

```
-bash:/tmp/2608/c:$ git pull ../b.git/
warning: no common commits
remote: Counting objects: 3, done.
remote: Total 3 (delta 0), reused 0 (delta 0)
Unpacking objects: 100% (3/3), done.
From ../b
 * branch            HEAD       -> FETCH_HEAD
fatal: refusing to merge unrelated histories
```

3. actual result
================
pulls out, removes all files from the first tree

4. the difference and why it was unexpected
===========================================
I can’t find words on it … it should not work but it did? somehow … with unexpected results to my local repository

it somehow seems to be an issue of my config, because resetting it, will not allow the pull as expected

```
-bash:/tmp/2608/c:$ GIT_CONFIG_NOSYSTEM=1 HOME=. git config -l
core.repositoryformatversion=0
core.filemode=true
core.bare=false
core.logallrefupdates=true
core.ignorecase=true
core.precomposeunicode=true
remote.origin.url=/tmp/2608/a.git
remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
branch.master.remote=origin
branch.master.merge=refs/heads/master


-bash:/tmp/2608/c:$ GIT_CONFIG_NOSYSTEM=1 HOME=. git pull ../b.git/
warning: no common commits
remote: Counting objects: 3, done.
remote: Total 3 (delta 0), reused 0 (delta 0)
Unpacking objects: 100% (3/3), done.
From ../b
 * branch            HEAD       -> FETCH_HEAD
fatal: refusing to merge unrelated histories


-bash:/tmp/2608/c:$ git pull ../b.git/
From ../b
 * branch            HEAD       -> FETCH_HEAD
Successfully rebased and updated refs/heads/master.
```

the logs tells me he rebases ...
```
-bash:/tmp/2608/c:$ git config -l | grep merge
diff.tool=p4merge
merge.tool=p4merge
merge.branchdesc=true
merge.log=true
branch.autosetupmerge=true
branch.master.merge=refs/heads/master


-bash:/tmp/2608/c:$ git config -l | grep pull
pull.rebase=preserve


-bash:/tmp/2608/c:$ git config -l | grep fetch
fetch.recursesubmodules=true
remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
```


> I suspect that this information is in your message, somewhere, but it
> is (understandably) unfocussed and I am having trouble pulling it out.
> 

I’m sorry, I just wanted to write down first any helpful information without - being late - having time to go into further investigations myself … hopefully to get some answers that „this is ok, you’re just stupid and didn’t read the spec/doc“ or „ok, this seems strange to me too, can we go forward in details and analysis“ ;)

> [...]
>> trying to fix this up by doing another pull failed:
>> ```
>> -bash:$ git remote -v
>> origin	git@bitbucket.org:childnode/marcel.git (fetch)
>> origin	git@bitbucket.org:childnode/marcel.git (push)
>> 
>> -bash:$ git pull
>> fatal: refusing to merge unrelated histories
> 
> Ok, this part is something I might be able to help shed some light on.
> 
> Searching for 'unrelated' in "git help pull" finds:
> 
>       --allow-unrelated-histories
> 	   By default, git merge command refuses to merge histories that do not
> 	   share a common ancestor. This option can be used to override this
> 	   safety when merging histories of two projects that started their
> 	   lives independently. As that is a very rare occasion, no
> 	   configuration variable to enable this by default exists and will not
> 	   be added.
> 
> So that explains the "what" of that error message.
> 
> The "why" is a separate question.  Could you share output from
> 
>  git log --all --graph --decorate --oneline --simplify-by-decoration
> 
> and
> 
>  git status
> 

```
-bash:/tmp/2608/c:$ git status
On branch master
Your branch and 'origin/master' have diverged,
and have 1 and 1 different commits each, respectively.
  (use "git pull" to merge the remote branch into yours)

nothing to commit, working tree clean


-bash:/tmp/2608/c:$ git branch -avv
* master                80b0355 [origin/master: ahead 1, behind 1] bar
  remotes/origin/HEAD   -> origin/master
  remotes/origin/master ed191c4 foo

```


> to help us understand your current state?
> 
> Also, suggestions for improvements to the 'refusing to merge' message
> would be very welcome.
> 
> Thanks and hope that helps,
> Jonathan

just to say: the latter „refused pull“ is what I expect the first time too!


SUSPECTED / PROVEN to found a guilty setting
=============================================
```
-bash:/tmp/2608/c:$ GIT_CONFIG_NOSYSTEM=1 HOME=. git -c user.name="me" -c user.email=me@example.com pull -r ../b.git/
warning: no common commits
remote: Counting objects: 3, done.
remote: Total 3 (delta 0), reused 0 (delta 0)
Unpacking objects: 100% (3/3), done.
From ../b
 * branch            HEAD       -> FETCH_HEAD
First, rewinding head to replay your work on top of it...
Applying: foo


-bash:/tmp/2608/c:$ ll
total 0
drwxr-xr-x  14 marcel  wheel   448B 23 Feb 06:21 .git
-rw-r--r--   1 marcel  wheel     0B 23 Feb 06:21 bar
-rw-r--r--   1 marcel  wheel     0B 23 Feb 06:21 foo

```
shows me a quite different behavior, so solely rebase not seems the full problem
BUT
`--rebase=preserve` will .. o’man , really, is this intended?

Yes, I see, rebase is a harmful operation and yes, you might now tell me a fool
to apply this per default

but why is this unrelated history check different from pull (merge) to rebase to rebase -p ?
Can’t find a word on it
https://git-scm.com/docs/git-rebase#git-rebase---preserve-merges


With regards,
~Marcel