为什么git在合并期间会产生冲突，而大多数kbin3之类的合并工具会自动解决该冲突？

Question

As stated in the title. I tried googling this but found no explanation for it so I looked at the kdiff3 documentation which provided some insight. The situation i'm running into is I do a merge from one branch into another, get a bunch of conflicts and use git mergetool to resolve them one by one. What happens is that for some files when kdiff3 is started, it pops up a dialog that there were x auto resolved conflicts and that there are no conflicts left so i save the file and continue.

According to kdiff3 documentation, conflicts are auto resolved if the line was changed in only one version of the file. Ie. the base is the same as the local or remote file, but not both.

My question is, if my merge tool can auto-resolve this(i've tried a few and they all auto resolve some conflicts) and indeed it seems logical what it does, why do I even get a conflict from git?

A follow up question is: how can I make git auto-resolve these conflicts before i even pop open my merge tool?

An example would be:

base:
line 1
line 2
line 3

local:
line 1
line 2
line 3

remote:
line 1
line abc
line 3

I think the above conflicts in Git but is auto resolved in kdiff3. Though it might be a different case, i've done merges that were auto-resolved before, can't remember the exact scenario since it auto-resolved.

Answer 1

There could be a number of reasons, but most likely due to a difference in merge preferences.

Some examples of differences which kdiff3 can be configured to ignore:

• white space: an empty line and a line with four spaces
• comments: /* This is the original comment */ and /* This is the modified comment */
• numbers: number_of_diffs = 3 and number_of_diffs = 7

In each of those cases (and potentially many more) kdiff3 may just ignore the differences, thereby having no problem merging. Git, on the other hand, will make you manually resolve the conflicts.

In your example, there is no obvious reason why any (reasonable) tool would issue a merge-conflict. But what if the base file had been created in Linux, whilst you had edited the local file in Windows (or vice versa)? Then, possibly, the line-endings would have changed. This would probably be completely invisible to you but would cause a merge conflict. I've just tried it and got the following output:

Auto-merging file.txt
CONFLICT (content): Merge conflict in file.txt
Automatic merge failed; fix conflicts and then commit the result.

I then ran:

$ git mergetool
merge tool candidates: meld opendiff kdiff3 tkdiff xxdiff tortoisemerge gvimdiff diffuse ecmerge p4merge araxis bc3 codecompare emerge vimdiff
Merging:
file.txt

Normal merge conflict for 'file.txt':
  {local}: modified file
  {remote}: modified file
Hit return to start merge resolution tool (kdiff3):

Upon hitting return, kdiff3 silently merged the two files (I didn't even see it open) happily resolving the whitespace difference.

That may not be exactly what is happening in your case, but it's a real example of Git failing to merge what kdiff3 auto-resolves simply because of whitespace.