From: Sebastian Kuzminsky <hidden> Date: 2016-06-15 22:53:49
Hi folks, I just ran in to a strange behavior with git merge.
Things start out with two branches (let's call them 'master' and 'other') pointing at a particular commit. In master I commit a small one-line change, then make a second commit that adds some stuff just after the line changed in the previous commit. In the other branch, i cherry-pick the second commit from master (the one that adds the new stuff). The cherry-pick succeeds, despite the fuzzy context. So far, so good.
Next I try to merge other into master. I expected it to notice there was nothing to do and leave the master tree unchanged, but it applied the "add new stuff" patch to master (even though that patch is already in master) and made a commit from that. So it silently did the wrong thing, and now the file contains two copies of stuff I added.
That is a simplified version of what happened, in my real repo there were several (unrelated and unimportant) commits on both master and the other branch. When the surprising double-add happened, i simplified the repo to remove distractions. The simplified repo is here if anyone wants to inspect it: https://github.com/SebKuzminsky/merge-problem
--
Sebastian Kuzminsky
From: Michael Witten <hidden> Date: 2016-06-15 22:53:49
On Fri, 11 May 2012 16:25:29 -0600, Sebastian Kuzminsky wrote:
Hi folks, I just ran in to a strange behavior with git merge.
Things start out with two branches (let's call them 'master' and
'other') pointing at a particular commit. In master I commit a
small one-line change, then make a second commit that adds some
stuff just after the line changed in the previous commit. In the
other branch, i cherry-pick the second commit from master (the
one that adds the new stuff). The cherry-pick succeeds, despite
the fuzzy context. So far, so good.
Next I try to merge other into master. I expected it to notice
there was nothing to do and leave the master tree unchanged,
but it applied the "add new stuff" patch to master (even though
that patch is already in master) and made a commit from that. So
it silently did the wrong thing, and now the file contains two
copies of stuff I added.
That is a simplified version of what happened, in my real repo
there were several (unrelated and unimportant) commits on both
master and the other branch. When the surprising double-add
happened, i simplified the repo to remove distractions.
The simplified repo is here if anyone wants to inspect it:
https://github.com/SebKuzminsky/merge-problem
It would obviously be helpful to supply:
* Explicit commands that anyone on the list can try and discuss.
For example:
git init repo
cd repo
echo a > a; git add a; git commit -m 'small one-line change'
echo b >> a; git commit -am 'adds some stuff after'
...
* Expected behavior from those commands.
* Actual behavior from those commands.
In other words, rather than burdening people with the task of
constructing a mental picture of what you have done, you should
show them as directly and precisely as possible; in this way,
people can go about the business of discussing your issue much
more quickly and, most importantly, PRECISELY.
Sincerely,
Michael Witten
In other words, rather than burdening people with the task of
constructing a mental picture of what you have done, you should
show them as directly and precisely as possible; in this way,
people can go about the business of discussing your issue much
more quickly and, most importantly, PRECISELY.
Ah, I had intended the extremely tiny git repo I linked to to provide
the info in the most concise way possible. The surprising behaviour
happened at the final commit in the repo, which was made by 'git merge
other'.
I can email a list of commands to reproduce the issue later tonight if
that would make anything clearer.
--
Sebastian Kuzminsky
In other words, rather than burdening people with the task of
constructing a mental picture of what you have done, you should
show them as directly and precisely as possible; in this way,
people can go about the business of discussing your issue much
more quickly and, most importantly, PRECISELY.
Ah, I had intended the extremely tiny git repo I linked to to provide
the info in the most concise way possible. The surprising behaviour
happened at the final commit in the repo, which was made by 'git merge
other'.
I can email a list of commands to reproduce the issue later tonight if
that would make anything clearer.
The repository you provided is actually quite simple and clear, though I
have no idea why this might be happening. Or if it is an expected behavior.
At the same time if you provide a list of command if someone will be
fixing this they may server as an automated test. Git has a lot of them.
--
Illia Bobyr
From: Sebastian Kuzminsky <hidden> Date: 2016-06-15 22:53:49
Here's a little script that reproduces the problem:
-----
#!/bin/bash
set -e
if [ -e git-merge-problem ]; then
echo "'git-merge-problem' exists, not running test!"
exit 1
fi
mkdir git-merge-problem
cd git-merge-problem
git init
echo "first line" > myfile
echo "second line" >> myfile
echo "" >> myfile
echo "next to last line" >> myfile
echo "final line" >> myfile
git add myfile
git commit -m 'initial commit of myfile'
git branch other
sed -i -e 's/second line/this line is in the context of the crucial patch/' myfile
git add myfile
git commit -m 'change context for crucial patch'
sed -i -e 's/^$/\nthis line is added only once, but in two branches\n/' myfile
git add myfile
git commit -m 'add a line'
git tag add-a-line
git checkout other
git cherry-pick -x add-a-line
git checkout master
git merge other
NUM_LINES=$(grep 'added only once' myfile | wc -l)
if [ $NUM_LINES -eq 2 ]; then
echo "FAIL! the merge added the line twice"
cat myfile
exit 1
elif [ $NUM_LINES -ne 1 ]; then
echo "FAIL! the merge added the line a strange number of times ($NUM_LINES)"
exit 1
fi
echo "PASS! the merge added the line just once!"
exit 0
-----
On May 11, 2012, at 20:25 , Illia Bobyr wrote:
On 5/11/2012 5:05 PM, Sebastian Kuzminsky wrote:
quoted
On 05/11/2012 05:57 PM, Michael Witten wrote:
quoted
On Fri, 11 May 2012 16:25:29 -0600, Sebastian Kuzminsky wrote:
In other words, rather than burdening people with the task of
constructing a mental picture of what you have done, you should
show them as directly and precisely as possible; in this way,
people can go about the business of discussing your issue much
more quickly and, most importantly, PRECISELY.
Ah, I had intended the extremely tiny git repo I linked to to provide
the info in the most concise way possible. The surprising behaviour
happened at the final commit in the repo, which was made by 'git merge
other'.
I can email a list of commands to reproduce the issue later tonight if
that would make anything clearer.
The repository you provided is actually quite simple and clear, though I
have no idea why this might be happening. Or if it is an expected behavior.
At the same time if you provide a list of command if someone will be
fixing this they may server as an automated test. Git has a lot of them.
--
Illia Bobyr