diff --git a/mercurial/dirstate.py b/mercurial/dirstate.py
--- a/mercurial/dirstate.py
+++ b/mercurial/dirstate.py
@@ -381,39 +381,10 @@ class dirstate(object):
         oldp2 = self._pl[1]
         if self._origpl is None:
             self._origpl = self._pl
-        self._map.setparents(p1, p2)
-        copies = {}
         nullid = self._nodeconstants.nullid
-        if oldp2 != nullid and p2 == nullid:
-            candidatefiles = self._map.non_normal_or_other_parent_paths()
-
-            for f in candidatefiles:
-                s = self._map.get(f)
-                if s is None:
-                    continue
-
-                # Discard "merged" markers when moving away from a merge state
-                if s.merged:
-                    source = self._map.copymap.get(f)
-                    if source:
-                        copies[f] = source
-                    self._map.reset_state(
-                        f,
-                        wc_tracked=True,
-                        p1_tracked=True,
-                        possibly_dirty=True,
-                    )
-                # Also fix up otherparent markers
-                elif s.from_p2:
-                    source = self._map.copymap.get(f)
-                    if source:
-                        copies[f] = source
-                    self._map.reset_state(
-                        f,
-                        p1_tracked=False,
-                        wc_tracked=True,
-                    )
-        return copies
+        # True if we need to fold p2 related state back to a linear case
+        fold_p2 = oldp2 != nullid and p2 == nullid
+        return self._map.setparents(p1, p2, fold_p2=fold_p2)
 
     def setbranch(self, branch):
         self.__class__._branch.set(self, encoding.fromlocal(branch))
diff --git a/mercurial/dirstatemap.py b/mercurial/dirstatemap.py
--- a/mercurial/dirstatemap.py
+++ b/mercurial/dirstatemap.py
@@ -428,9 +428,40 @@ class dirstatemap(object):
 
         return self._parents
 
-    def setparents(self, p1, p2):
+    def setparents(self, p1, p2, fold_p2=False):
         self._parents = (p1, p2)
         self._dirtyparents = True
+        copies = {}
+        if fold_p2:
+            candidatefiles = self.non_normal_or_other_parent_paths()
+
+            for f in candidatefiles:
+                s = self.get(f)
+                if s is None:
+                    continue
+
+                # Discard "merged" markers when moving away from a merge state
+                if s.merged:
+                    source = self.copymap.get(f)
+                    if source:
+                        copies[f] = source
+                    self.reset_state(
+                        f,
+                        wc_tracked=True,
+                        p1_tracked=True,
+                        possibly_dirty=True,
+                    )
+                # Also fix up otherparent markers
+                elif s.from_p2:
+                    source = self.copymap.get(f)
+                    if source:
+                        copies[f] = source
+                    self.reset_state(
+                        f,
+                        p1_tracked=False,
+                        wc_tracked=True,
+                    )
+        return copies
 
     def read(self):
         # ignore HG_PENDING because identity is used only for writing
@@ -769,9 +800,40 @@ if rustmod is not None:
                 # File doesn't exist, so the current state is empty
                 return b''
 
-        def setparents(self, p1, p2):
+        def setparents(self, p1, p2, fold_p2=False):
             self._parents = (p1, p2)
             self._dirtyparents = True
+            copies = {}
+            if fold_p2:
+                candidatefiles = self.non_normal_or_other_parent_paths()
+
+                for f in candidatefiles:
+                    s = self.get(f)
+                    if s is None:
+                        continue
+
+                    # Discard "merged" markers when moving away from a merge state
+                    if s.merged:
+                        source = self.copymap.get(f)
+                        if source:
+                            copies[f] = source
+                        self.reset_state(
+                            f,
+                            wc_tracked=True,
+                            p1_tracked=True,
+                            possibly_dirty=True,
+                        )
+                    # Also fix up otherparent markers
+                    elif s.from_p2:
+                        source = self.copymap.get(f)
+                        if source:
+                            copies[f] = source
+                        self.reset_state(
+                            f,
+                            p1_tracked=False,
+                            wc_tracked=True,
+                        )
+            return copies
 
         def parents(self):
             if not self._parents: