diff --git a/mercurial/filemerge.py b/mercurial/filemerge.py
--- a/mercurial/filemerge.py
+++ b/mercurial/filemerge.py
@@ -532,6 +532,17 @@
     return _imerge(repo, mynode, orig, fcd, fco, fca, toolconf, files, labels)
 
 
+@internaltool(
+    b'merge3-lie-about-conflicts', fullmerge, b'', precheck=_mergecheck,
+)
+def _imerge3alwaysgood(*args, **kwargs):
+    b1, junk, b2 = _imerge3(*args, **kwargs)
+    # TODO is this right? I'm not sure what these return values mean,
+    # but as far as I can tell this will indicate to callers tha the
+    # merge succeeded.
+    return b1, False, b2
+
+
 def _imergeauto(
     repo,
     mynode,