Re: [BUG] rebase --interactive silently overwrites ignored files

[Phillip Wood <phillip.wood123@gmail.com>]

Hi wh

On 14/04/2019 02:59, wh wrote:
> Thanks for the info about the upcoming "precious" attribute. Looks useful.
> 
> I didn't get the impression that Git normally overwrites ignored
> files. I ran some more experiments:
> 
> git rebase FETCH_HEAD        # bails
> git rebase -i FETCH_HEAD     # overwrites
> git merge FETCH_HEAD         # bails
> git reset --keep FETCH_HEAD  # bails
> git reset --merge FETCH_HEAD # bails
> git checkout FETCH_HEAD      # overwrites
> # without feature 2 locally:
> git merge FETCH_HEAD         # overwrites, fast-forwards
> git merge --no-ff FETCH_HEAD # bails

I've had a look at the rebase -i code and I think it only overwrites 
ignored files when it is fast-forwarding. This matches what merge does 
when fast-forwarding but I'm not convinced either of them should be 
doing this by default (I think checkout doing it is probably asking for 
trouble), as you point out most operations preserve ignored files. When 
pull fast-forwards it does not overwrite ignored files.

Both checkout and merge have an undocumented --overwrite-ignore option 
which is on by default. Checkout and fast-forward merges overwriting 
ignored files dates back a long way to commit 1127148089 ("Loosen 
"working file will be lost" check in Porcelain-ish", 2006-12-04). There 
does not seem to have been much discussion of changing the semantics of 
ignored files around the patches that implemented this [1,2]. There is a 
brief mention of doing it in this thread [3] but no one seems to comment 
on the idea as far as I can see. Before this change ignored files were 
just ignored by status and add but otherwise treated like any other 
untracked file.

I'll put a patch together to fix rebase -i, I'd like to see the defaults 
for merge and checkout changed but I'm not sure that would be popular. 
It does seem like surprising behavior though when most operations try to 
preserve untracked files.

Best Wishes

Phillip

[1] 
https://public-inbox.org/git/7vlklnkv39.fsf@assigned-by-dhcp.cox.net/T/#u
[2] 
https://public-inbox.org/git/7vbqmjkuzd.fsf@assigned-by-dhcp.cox.net/T/#u
[3]https://public-inbox.org/git/Pine.LNX.4.64.0610081657400.3952@g5.osdl.org/

> On Fri, Apr 12, 2019 at 9:30 AM Phillip Wood <phillip.wood123@gmail.com> wrote:
>>
>> Hi
>>
>> On 12/04/2019 00:56, wh wrote:
>>> I'm using git 2.20.1 from Debian. Git is usually careful not to
>>> overwrite untracked files, including ignored files.
>>
>> Git normally overwrites ignored files, so I think in your example rebase
>> -i is working as expected, I'm surprised that the am based rebase does
>> not overwrite the ignored file. There has been some discussion about
>> introducing 'precious' files that are ignored but protected in the same
>> way as untracked files [1].
>>
>> Best Wishes
>>
>> Phillip
>>
>> [1] https://public-inbox.org/git/20190409102649.22115-1-pclouds@gmail.com/
>>
>>    But interactive
>>> rebase doesn't detect this (non-interactive rebase works fine).
>>>
>>> Reproduction:
>>> -----
>>>
>>> #!/bin/sh
>>> mkdir upstream
>>> cd upstream
>>> git init
>>> echo 1 >feature-1
>>> git add feature-1
>>> git commit -m "feature 1"
>>>
>>> cd ..
>>> git clone upstream local
>>> cd local
>>> # write some tools for our own convenience
>>> echo ours >tools
>>> echo /tools >>.git/info/exclude
>>> # start working on a feature
>>> git checkout -b f2
>>> echo wip >feature-2
>>> git add feature-2
>>> git commit -m "wip"
>>>
>>> cd ../upstream
>>> # official tools are available
>>> echo theirs >tools
>>> git add tools
>>> git commit -m "tools"
>>>
>>> cd ../local
>>> git fetch ../upstream master
>>>
>>> # this would be okay
>>> #git rebase FETCH_HEAD
>>>
>>> # problem: overwrites tools silently
>>> GIT_EDITOR=true git rebase -i FETCH_HEAD
>>>
>>> cat tools
>>>
>>> -----
>>>
>>> Expected: `git rebase -i` fails because it would have to overwrite the
>>> untracked "tools" file. Contents of tools file remains `ours`.
>>>
>>> Actual: Contents of tools file becomes `theirs`.
>>>