diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -29,6 +29,7 @@ from . import (
     copies,
     debugcommands as debugcommandsmod,
     destutil,
+    diffutil,
     discovery,
     encoding,
     error,
@@ -2655,7 +2656,7 @@ def diff(ui, repo, *pats, **opts):
     if change:
         repo = scmutil.unhidehashlikerevs(repo, [change], b'nowarn')
         ctx2 = logcmdutil.revsingle(repo, change, None)
-        ctx1 = logcmdutil.diff_parent(ctx2)
+        ctx1 = diffutil.diff_parent(ctx2)
     elif from_rev or to_rev:
         repo = scmutil.unhidehashlikerevs(
             repo, [from_rev] + [to_rev], b'nowarn'
diff --git a/mercurial/diffutil.py b/mercurial/diffutil.py
--- a/mercurial/diffutil.py
+++ b/mercurial/diffutil.py
@@ -16,6 +16,7 @@ from typing import (
 )
 
 from .i18n import _
+from .node import nullrev
 
 from . import (
     mdiff,
@@ -155,3 +156,35 @@ def difffeatureopts(
         )
 
     return mdiff.diffopts(**pycompat.strkwargs(buildopts))
+
+
+def diff_parent(ctx):
+    """get the context object to use as parent when diffing
+
+
+    If diff.merge is enabled, an overlayworkingctx of the auto-merged parents will be returned.
+    """
+    repo = ctx.repo()
+    if repo.ui.configbool(b"diff", b"merge") and ctx.p2().rev() != nullrev:
+        # avoid circular import
+        from . import (
+            context,
+            merge,
+        )
+
+        wctx = context.overlayworkingctx(repo)
+        wctx.setbase(ctx.p1())
+        with repo.ui.configoverride(
+            {
+                (
+                    b"ui",
+                    b"forcemerge",
+                ): b"internal:merge3-lie-about-conflicts",
+            },
+            b"merge-diff",
+        ):
+            with repo.ui.silent():
+                merge.merge(ctx.p2(), wc=wctx)
+        return wctx
+    else:
+        return ctx.p1()
diff --git a/mercurial/logcmdutil.py b/mercurial/logcmdutil.py
--- a/mercurial/logcmdutil.py
+++ b/mercurial/logcmdutil.py
@@ -11,18 +11,18 @@ import os
 import posixpath
 
 from .i18n import _
-from .node import nullrev, wdirrev
+from .node import wdirrev
 
 from .thirdparty import attr
 
 from . import (
     dagop,
+    diffutil,
     error,
     formatter,
     graphmod,
     match as matchmod,
     mdiff,
-    merge,
     patch,
     pathutil,
     pycompat,
@@ -69,35 +69,6 @@ def getlimit(opts):
     return limit
 
 
-def diff_parent(ctx):
-    """get the context object to use as parent when diffing
-
-
-    If diff.merge is enabled, an overlayworkingctx of the auto-merged parents will be returned.
-    """
-    repo = ctx.repo()
-    if repo.ui.configbool(b"diff", b"merge") and ctx.p2().rev() != nullrev:
-        # avoid cycle context -> subrepo -> cmdutil -> logcmdutil
-        from . import context
-
-        wctx = context.overlayworkingctx(repo)
-        wctx.setbase(ctx.p1())
-        with repo.ui.configoverride(
-            {
-                (
-                    b"ui",
-                    b"forcemerge",
-                ): b"internal:merge3-lie-about-conflicts",
-            },
-            b"merge-diff",
-        ):
-            with repo.ui.silent():
-                merge.merge(ctx.p2(), wc=wctx)
-        return wctx
-    else:
-        return ctx.p1()
-
-
 def get_diff_chunks(
     ui,
     repo,
@@ -273,7 +244,7 @@ class changesetdiffer:
             ui,
             ctx.repo(),
             diffopts,
-            diff_parent(ctx),
+            diffutil.diff_parent(ctx),
             ctx,
             match=self._makefilematcher(ctx),
             stat=stat,
@@ -286,7 +257,7 @@ class changesetdiffer:
             ui,
             ctx.repo(),
             diffopts,
-            diff_parent(ctx),
+            diffutil.diff_parent(ctx),
             ctx,
             match=self._makefilematcher(ctx),
             stat=stat,