IntelliJ IDEA has a really awesome merge tool, which works great if you use the merge tools built into the IDE. However, if you prefer the command line (which you can use without leaving your IDE), setting up the tools are a bit more complicated.

To begin with, if your IDE is installed in the default Program Files (x86), you will need to create a symlink to your IntelliJ IDEA directory. The path to this symlink should not have any weird characters in it.

mlink /D C:\workspace\tools\idea "C:\Program Files (x86)\JetBrains\IntelliJ IDEA 2016.2"

The next step is to tell Git to use IDEA as your difftool, using the symlink. However, there is another issue: the IDEA startup script (idea.bat) is a Windows batch script, while the Git bash shell makes use of *nix bash scripts. Fortunately, it is possible to invoke cmd.exe with arguments. The specific command we are looking for is

cmd /C "<path to idea.bat> <any other arguments>"

At this point, we just need to figure out which arguments to pass to idea.bat and then add it to the .gitconfig file. Looking at the Jetbrains documentation, using IDEA as a difftool seems pretty simple: just pass diff as the first argument, followed by two file names. It is more or less the same thing with merging: pass merge followed by the two conflicting files, the base file and the output file. However, how will this work with Git history?

The IDEA documentation gives a link to a nice blog post explaining how to set this up for Mac, which we can use to figure out the Windows structure:

# merge
cmd = idea merge $(cd $(dirname "$LOCAL") && pwd)/$(basename "$LOCAL") $(cd $(dirname "$REMOTE") && pwd)/$(basename "$REMOTE") $(cd $(dirname "$BASE") && pwd)/$(basename "$BASE") $(cd $(dirname "$MERGED") && pwd)/$(basename "$MERGED")
# diff
cmd = idea diff $(cd $(dirname "$LOCAL") && pwd)/$(basename "$LOCAL") $(cd $(dirname "$REMOTE") && pwd)/$(basename "$REMOTE")

So now we have everything we need:

• A symlink to the IDEA progrom folder with no special characters
• A command to invoke Windows batch scripts from a bash shell
• The paramaters we need to pass idea.bat to make it diff and merge

The final part of the puzzle is figuring out which special characters to escape when setting up the Git commands. The result (added to .gitconfig):

[mergetool "intellij"]
	cmd = cmd \"/C D:\\workspace\\tools\\symlink\\idea\\bin\\idea.bat merge $(cd $(dirname "$LOCAL") && pwd)/$(basename "$LOCAL") $(cd $(dirname "$REMOTE") && pwd)/$(basename "$REMOTE") $(cd $(dirname "$BASE") && pwd)/$(basename "$BASE") $(cd $(dirname "$MERGED") && pwd)/$(basename "$MERGED")\"
[difftool "intellij"]
	cmd = cmd \"/C D:\\workspace\\tools\\symlink\\idea\\bin\\idea.bat diff $(cd $(dirname "$LOCAL") && pwd)/$(basename "$LOCAL") $(cd $(dirname "$REMOTE") && pwd)/$(basename "$REMOTE")\"

The final step is to tell Git to make use of the configured intellij commands:

[merge]
    tool = intellij
[diff]
    tool = intellij
    guitool = intellij

My full .gitconfig file is available as a Gist.