Why won't Mercurial merge my XML files with Beyond Compare?

Question

We have a bunch of XML files in our Mercurial repository. When we merge changes in those files from one branch to another, Mercurial complains that some of our XML files are binary , and asks me to choose between the local and other versions of the file.

I've discovered that Mercurial thinks any file with a NULL byte in it is binary, and some of our XML files are encoded as UTF-16, so contain a lot of NULL bytes. My default merge tool is Beyond Compare , which can handle UTF-16 encoded files. I've configured Mercurial as recommended on the Beyond Compare website , but during the merge, Mercurial says:

tool bcomp can't handle binary

What gives? Why does Mercurial think Beyond Compare can't merge my file?

Answer 1

The recommended Mercurial configuration to use Beyond Compare as a merge program looks like this:

[merge-tools]
bcomp.executable = C:\Program Files\Beyond Compare 3\BComp.exe
bcomp.args = $local $other $base $output
bcomp.priority = 1
bcomp.premerge = True
bcomp.gui = True

[ui]
merge = bcomp

According to the Mercurial docs on merge tools , there is a binary option that is False by default. When binary=True , it tells Mercurial the tool can merge binary files. When I turn that option on, however, Mercurial still won't let Beyond Compare merge the XML files.

A little more research turns up the premerge option. When premerge=True , Mercurial merges internally first , and use the merge tool only if there are conflicts to be resolved. Unfortunately, Mercurial always fails to merge a binary file. When a pre-merge fails, Mercurial stops the merge for that file and never launches the merge tool.

The solution would seem to be, then, to also set the premerge option to False . Unfortunately, the pre-merge is very helpful because 90% of the time, there aren't any conflicts, and never see your merge tool. With premerge set to False , every time a merge is needed, Beyond Compare opens. This gets very tedious.

To solve this, I created a second Beyond Compare merge tool configuration which gets used to merge binary files . I set its priority lower than the default bcomp tool, so it only gets called when the main bcomp tool fails, which is usually just for binary files. I added these lines to the merge-tools section of my mercurial.ini file:

bcompbin.executable = C:\Program Files (x86)\Beyond Compare 3\BCompare.exe
bcompbin.args = $local $other $base $output
bcompbin.gui = True
bcompbin.premerge = False
bcompbin.binary = True

One of the side-effects of this is that Beyond Compare will launch to merge binary files for which it can't handle. I haven't encountered that situation yet, so don't know how to handle it. I would probably just temporarily comment out my bcompbin merge tool.