Re: [Bug] git stash generates a different diff then other commands (diff, add, etc) resulting in merge conflicts!

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On 08/12/2013 12:05 PM, Phil Hord wrote:
On Mon, Aug 12, 2013 at 1:29 AM, Luke San Antonio
<lukesanantonio@xxxxxxxxx> wrote:
On 08/08/20130 04:54 PM, Phil Hord wrote:
Luke,

I think the issue is that your working directory receives your cached
file when you say 'git stash --keep-index'.  When you restore the
stash, your previous working directory now conflicts with your new
working directory, but neither is the same as HEAD.

Here's a test script to demonstrate the issue, I think.  Did I get
this right, Luke?

   # cd /tmp && rm -rf foo
   git init foo && cd foo
   echo "foo" > bar &&  git add bar && git commit -mfoo
   echo "bar" > bar &&  git add bar
   echo "baz" > bar
   echo "Before stash  bar: $(cat bar)"
   git stash --keep-index
   echo "After stash  bar: $(cat bar)"
   git stash apply
Actually no, in your script, the bar file has a modification in the working
tree which is in the same hunk as a change applied to the index. In my
project the changes that were added to the index are not modified further
in theworking tree.

--------

Not only that, but I found out why git was generated different patches!
I realized that when I removed a hunk appearing before the merge conflict
from the working tree and index, the merge conflict disappeared! Turns
out, we can forget about stashing for a minute!
First the hunk in my working tree:

@@ -56,12 +56,14 @@
      bool running_ = true;


      /*!
-     * \brief The default font renderer, global to all who have a pointer
to
-     * the Game class.
+     * \brief The font renderer implementation, obtained from the config
file.
       *
-     * It need not be used at all!
+     * It should be used and passed along to member objects by GameStates!
+     *
+     * \note It can be cached, but not between GameStates, meaning it
should be
+     * cached again every time a new GameState is constructed!
       */
-    std::unique_ptr<FontRenderer> font_renderer_ = nullptr;
+    FontRenderer* font_renderer_ = nullptr;

      int run(int argc, char* argv[]);

Most of this is unimportant, but notice the line number spec:@@ -56,12
+56,14 @@
The line number of this hunk doesn't change! Then I addeda few lines *above*
this hunk, (around line 30 I think). Here is the diff again:

@@ -56,12 +58,14 @@
      bool running_ = true;


      /*!
-     * \brief The default font renderer, global to all who have a pointer
to
-     * the Game class.
+     * \brief The font renderer implementation, obtained from the config
file.
+     *
+     * It should be used and passed along to member objects by GameStates!
       *
-     * It need not be used at all!
+     * \note It can be cached, but not between GameStates, meaning it
should be
+     * cached again every time a new GameState is constructed!
       */
-    std::unique_ptr<FontRenderer> font_renderer_ = nullptr;
+    FontRenderer* font_renderer_ = nullptr;

      int run(int argc, char* argv[]);

Notice the new line number spec:@@ -56,12 +58,14 @@

It moves two lines down, because I added those two lines before it, makes
sense!
But also notice that the patches are different, just because of the two
lines
above it!

I thought I might be able to fix this problem by changing the new
diff.algorithm
config option to 'patience', but it seems to only affect how patches look,
not
how they are stored internally... Same problem!

Also, I'm wondering why that line was picked up by git if the patches don't
match,
shouldn't git give me a conflict with the whole hunk, or is the system
smarter
than that?
Git does not store patches.  Git stores the entire file.  I do not
think the diff algorithm you choose will have any effect on the
results of the merge.  But I am pretty clueless about the merge
engine, so I could be off-base on this last part.

What if merging suppressed the conflict if both possibilities are the same?
Isn't
that reasonable, or is there some 1% where this could cause (silent but
deadly)
data loss.
I think that is what Git is meant to do.  But I am confused now about
where the failure is occurring for you.  Can you demonstrate the
problem by modifying my test script?

Is this more like it?

   cd /tmp && rm -rf foo
   git init foo && cd foo
   printf "1\n2 foo\n3\n4\n5\n6\n7\n8 foo\n9\n10\n" > bar &&  git add bar
   git commit -mfoo
   printf "1\n2 XXX\n3\n4\n5\n6\n7\n8 foo\n9\n10\n" > bar &&  git add bar
   printf "1\n2 XXX\n3\n4\n5\n6\n7\n8 XXX\n9\n10\n" > bar
   echo "Before stash  bar: $(cat bar)"
   git stash --keep-index
   echo "After stash  bar: $(cat bar)"
   git stash apply

Phil
So I found an isolated case, it's very strange...

Here's a script!

  cd /tmp && rm -rf foo;
  git init foo && cd foo;
  git config --local diff.algorithm myers
  printf "\n\n-----------------\n\n\n    /*"'!'"\
\n     * ---------\n     * ^^^^^^^^^\n     *\n     \
* =========\n     */\n    |-----------|\n" > foo;
  git add foo && git commit -m "foo";
  printf "\n-----------------\n\n\n    /*"'!'"\
\n     * #########\n     *\n     * !!!!!!!!!\n     \
*\n     * @@@@@@@@@\n     * &&&&&&&&&\n     */\n    \
|===========|\n" > foo
  printf "s\nn\ny\ny\ny\n" | git add foo --patch > /dev/null
  git stash save --keep-index

Let me start off by apologizing for that! =D

... Copy and paste that into a terminal and you should have a recreated version of my repository there! Now that the file is partly stashed and partly in the index, check out the difference in diffs:

try:
  git diff --staged
then try:
  git stash show -p

You see the difference? Then pop the stash and you'll see a very obfuscated and verbose sample of what I am talking about!

Also, sorry about the typos in my last message, I guess I looked past them...

Thanks Phil, for you know, helping me out!
- Luke
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