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== Tutorial - merging conflicting changes ==

We learned how to deal with simple ["Merge"]s in TutorialMerge.

["Mercurial"] handles more complex ["Merge"] cases, too. It is not all that uncommon for two people to edit the exact same lines of a file, and then have to figure out what to do. These cases are called conflicts; figuring out what to do about a conflict is called resolving it.

Let's first create an artificial conflict situation. As we did previously, let's start by making a ["Clone"] of {{{my-hello}}}:

{{{
$ cd ..
$ hg clone my-hello my-hello-not-cvs
}}}

Now let's add a new line of output to {{{hello.c}}}:

{{{
$ cd my-hello-not-cvs
$ vi hello.c
}}}

We change {{{main}}} to read like this:

{{{#!cplusplus numbers=off
int main(int argc, char **argv)
{
        printf("hello, world!\n");
        printf("sure am glad I'm not using CVS!\n");
        return 0;
}
}}}

And we ["Commit"] the change:

{{{
$ hg commit -m "Give thanks for dodging bullet"
}}}

Recall that in TutorialFirstChange, we created a ChangeSet in {{{my-hello-new-output}}} that ''also'' added a second line of output. What happens when we try to ["Pull"] that change in here?

{{{
$ hg pull ../my-hello-new-output
pulling from ../my-hello-new-output
searching for changes
adding changesets
adding manifests
adding file changes
added 1 changesets with 1 changes to 1 files (+1 heads)
(run 'hg update' to get a working copy)
}}}

So far, so good. Let's try an ["Update"].

{{{
$ hg update
this update spans a branch affecting the following files:
 hello.c (resolve)
aborting update spanning branches!
(use 'hg merge' to merge across branches or 'hg update -C' to lose changes)
}}}

As in TutorialMerge, we have to run {{{hg merge}}}. As before,
the MergeProgram will be started under cover. It will usually not be able to ["Merge"] automatically, because the same line of the same source file has been modified in a different way by each ChangeSet (the one we just ["Commit"]ted, and the one we just ["Pull"]ed).

{{{
$ hg merge
}}}

At this point, what happens depends on what programs are installed on our computer. If we are provident or lucky, and have a graphical MergeProgram installed, we will be able to see what conflicts there are between the two changes, and decide how to resolve them.

["Mercurial"] is using a per-file 3-way merge. This means that there are 3 input files for merging process, and those are:
 * Local file (from current repository)
 * Other file (from repository being merged)
 * Base file (last version of file before branches separated)

For more information about 3-way, see [http://revctrl.org/ThreeWayMerge ThreeWayMerge] on the [http://revctrl.org/ Revctrl wiki].

Else, if we do not have a graphical MergeProgram installed, we will be dropped into a text editor, which will be visiting the file we need to ["Merge"]. Doing this by hand is '''highly''' error-prone and tedious. It is best to exit the editor and use the {{{hg rollback}}} command to reverse the effect of the ["Pull"], then install a MergeProgram, and then try again.

(~-Note: before Mercurial version 0.9, `hg update -m` should have been used in place of `hg merge` and `hg undo` should have been used instead of `hg rollback`-~).


Now let's continue and finish on to TutorialConclusion.
Santa Rosa-born Shondra Martin is addicted to [[http://confhome.kaist.ac.kr/xe/?document_srl=2245179|Costa Blanca weather April,]] rc airplanes, saltwater aquariums. And lastly, she is fascinated by spending spare time with her great friends.

Santa Rosa-born Shondra Martin is addicted to Costa Blanca weather April, rc airplanes, saltwater aquariums. And lastly, she is fascinated by spending spare time with her great friends.

TutorialConflict (last edited 2019-03-28 10:43:14 by IanMoody)