Visual Studio as fallback mergetool doesn't work properly

I'm trying to use Visual Studio's 'vsDiffMerge' as a fallback tool for Unity's 'UnityYAMLMerge', so I can manually handle some of the more complicated merge conflicts. I'm using git (msys2), by the way.

The problem is, whenever I run 'git mergetool', VS opens its difftool instead of a mergetool.

Here are the steps I've gone through so far:
1) Changed Unity's Editor settings to: 'Visible Meta Files' and 'Force Text'
2) Added 'UnityYAMLMerge' as a default mergetool inside git's config file as shown in Unity Docs:
3) Following advice given here , modified 'mergespecfile.txt' in a following manner:

unity use "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\IDE\CommonExtensions\Microsoft\TeamFoundation\Team Explorer\vsDiffMerge.exe" "%r" "%l" "%b" "%d" /m

prefab use "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\IDE\CommonExtensions\Microsoft\TeamFoundation\Team Explorer\vsDiffMerge.exe" "%r" "%l" "%b" "%d" /m

* use "C:\Program Files (x86)\Microsoft Visual Studio\2017\Community\Common7\IDE\CommonExtensions\Microsoft\TeamFoundation\Team Explorer\vsDiffMerge.exe" "%r" "%l" "%b" "%d" /m

4) Tried fiddling with the slashes/backslashes and with the order of switches/arguments, nothing really helped.

Once again, theoretically there is no explicit "error" showing - VS merge tools simply doesn't open. Instead I'm stuck with the built-in difftool, which is not even half as helpful.

As a side note - I tried 2 additional things:
1) Running the merge operation from VS' git plugin - the result being more or less the same.
2) When notified about a conflict taking place, I explicitly used vsDiffMerge with a following path setting:

cmd = \"C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\Community\\Common7\\IDE\\CommonExtensions\\Microsoft\\TeamFoundation\\Team Explorer\\vsDiffMerge.exe\" \"$REMOTE\" \"$LOCAL\" \"$BASE\" \"$MERGED\" //m

And it actually worked - VS' Mergetool opened properly.

Now the thing is - why opening it manually works and re-directing to it via UnityYAMLMerge doesn't and what can I do to fix it?

 

Okay so it turns out that the only (probably) problem is that vsDiffMerge switches are not executed in any way when specified in 'mergespecfile'.

As a result:
unity use "path/to/the/tool/vsDiffMerge.exe" %l %r %b %d /m
is treated equally to:
unity use "path/to/the/tool/vsDiffMerge.exe" %l %r
And that, what a surprise, is supposed to (and well - does it) open the diff tool for files %l and %r.

Having that said, it remains a mystery to me how to pass the "/m" switch via 'mergespecfile'.

 

I had the same problem, but I finally found a solution.

It seems like the problem was the correct placement of the /m in the mergespecfile.txt

Here are the settings that worked for me, using Windows with Unity version 2020.3.18f1:


1) Unity settings

Edit>Project Settings>Version Control>Mode>Visible Meta Files

Edit>Project Settings>Editor>Asset Serialization>Mode>Force Text


2) Setup UnityYAMLMerge as a merge tool in git

git config --add merge.tool unityyamlmerge

git config --add mergetool.keepBackup false

git config --add mergetool.unityyamlmerge.trustExitCode false

git config --add mergetool.unityyamlmerge.cmd '"C:\Program Files\Unity\Hub\Editor\2020.3.18f1\Editor\Data\Tools\UnityYAMLMerge.exe" merge -p "$BASE" "$REMOTE" "$LOCAL" "$MERGED"'

This should result in the following local .config settings
[merge]
tool = unityyamlmerge
[mergetool]
keepBackup = false
[mergetool "unityyamlmerge"]
trustExitCode = false
cmd = \"C:\\Program Files\\Unity\\Hub\\Editor\\2020.3.18f1\\Editor\\Data\\Tools\\UnityYAMLMerge.exe\" merge -p \"$BASE\" \"$REMOTE\" \"$LOCAL\" \"$MERGED\"


3) Setup the mergespecfile.txt for vsDiffMerge

…

unity use "%programs%\Microsoft Visual Studio\2019\Community\Common7\IDE\CommonExtensions\Microsoft\TeamFoundation\Team Explorer\vsDiffMerge.exe" /m "%l" "%r" "%b" "%d"
prefab use "%programs%\Microsoft Visual Studio\2019\Community\Common7\IDE\CommonExtensions\Microsoft\TeamFoundation\Team Explorer\vsDiffMerge.exe" /m "%l" "%r" "%b" "%d"

#
# Default fallbacks for unknown files. First tool found is used.
#

# Windows vsDiffMerge
* use "%programs%\Microsoft Visual Studio\2019\Community\Common7\IDE\CommonExtensions\Microsoft\TeamFoundation\Team Explorer\vsDiffMerge.exe" /m "%l" "%r" "%b" "%d"

…


If it does not let you modify the file, “Right Click”>Properties>Security>Edit and allow Users to modify the file.


I hope it helps!