diff --git a/mercurial/debugcommands.py b/mercurial/debugcommands.py
--- a/mercurial/debugcommands.py
+++ b/mercurial/debugcommands.py
@@ -272,7 +272,9 @@
                             x[fn].data() for x in (pa, p1, p2)
                         ]
                         m3 = simplemerge.Merge3Text(base, local, other)
-                        ml = [l.strip() for l in simplemerge.merge_lines(m3)[0]]
+                        ml = [
+                            l.strip() for l in simplemerge.render_markers(m3)[0]
+                        ]
                         ml.append(b"")
                     elif at > 0:
                         ml = p1[fn].data().split(b"\n")
diff --git a/mercurial/simplemerge.py b/mercurial/simplemerge.py
--- a/mercurial/simplemerge.py
+++ b/mercurial/simplemerge.py
@@ -341,7 +341,7 @@
     return result
 
 
-def merge_lines(
+def render_markers(
     m3,
     name_a=None,
     name_b=None,
@@ -390,7 +390,7 @@
     return lines, conflicts
 
 
-def _mergediff(m3, name_a, name_b, name_base):
+def render_mergediff(m3, name_a, name_b, name_base):
     lines = []
     conflicts = False
     for what, group_lines in m3.merge_groups():
@@ -500,7 +500,7 @@
             [localctx.path(), otherctx.path(), None], opts.get('label', [])
         )
         if mode == b'mergediff':
-            lines, conflicts = _mergediff(m3, name_a, name_b, name_base)
+            lines, conflicts = render_mergediff(m3, name_a, name_b, name_base)
         else:
             extrakwargs = {
                 'minimize': True,
@@ -509,7 +509,7 @@
                 extrakwargs['base_marker'] = b'|||||||'
                 extrakwargs['name_base'] = name_base
                 extrakwargs['minimize'] = False
-            lines, conflicts = merge_lines(
+            lines, conflicts = render_markers(
                 m3, name_a=name_a, name_b=name_b, **extrakwargs
             )
 
diff --git a/tests/test-simplemerge.py b/tests/test-simplemerge.py
--- a/tests/test-simplemerge.py
+++ b/tests/test-simplemerge.py
@@ -179,7 +179,9 @@
 
         self.assertEqual(list(m3.merge_regions()), [(b'a', 0, 2)])
 
-        self.assertEqual(simplemerge.merge_lines(m3), ([b'aaa', b'bbb'], False))
+        self.assertEqual(
+            simplemerge.render_markers(m3), ([b'aaa', b'bbb'], False)
+        )
 
     def test_no_conflicts(self):
         """No conflicts because only one side changed"""
@@ -205,7 +207,7 @@
         )
 
         self.assertEqual(
-            b''.join(simplemerge.merge_lines(m3)[0]), b'aaa\nbbb\n222\n'
+            b''.join(simplemerge.render_markers(m3)[0]), b'aaa\nbbb\n222\n'
         )
 
     def test_append_b(self):
@@ -216,7 +218,7 @@
         )
 
         self.assertEqual(
-            b''.join(simplemerge.merge_lines(m3)[0]), b'aaa\nbbb\n222\n'
+            b''.join(simplemerge.render_markers(m3)[0]), b'aaa\nbbb\n222\n'
         )
 
     def test_append_agreement(self):
@@ -227,7 +229,7 @@
         )
 
         self.assertEqual(
-            b''.join(simplemerge.merge_lines(m3)[0]), b'aaa\nbbb\n222\n'
+            b''.join(simplemerge.render_markers(m3)[0]), b'aaa\nbbb\n222\n'
         )
 
     def test_append_clash(self):
@@ -237,7 +239,7 @@
             [b'aaa\n', b'bbb\n', b'333\n'],
         )
 
-        ml, conflicts = simplemerge.merge_lines(
+        ml, conflicts = simplemerge.render_markers(
             m3,
             name_a=b'a',
             name_b=b'b',
@@ -257,7 +259,7 @@
             [b'aaa\n', b'222\n', b'bbb\n'],
         )
 
-        ml, conflicts = simplemerge.merge_lines(
+        ml, conflicts = simplemerge.render_markers(
             m3,
             name_a=b'a',
             name_b=b'b',
@@ -298,7 +300,7 @@
             ],
         )
 
-        ml, conflicts = simplemerge.merge_lines(
+        ml, conflicts = simplemerge.render_markers(
             m3,
             name_a=b'a',
             name_b=b'b',
@@ -347,7 +349,7 @@
     def test_merge_poem(self):
         """Test case from diff3 manual"""
         m3 = Merge3(TZU, LAO, TAO)
-        ml, conflicts = simplemerge.merge_lines(m3, b'LAO', b'TAO')
+        ml, conflicts = simplemerge.render_markers(m3, b'LAO', b'TAO')
         self.log(b'merge result:')
         self.log(b''.join(ml))
         self.assertEqual(ml, MERGED_RESULT)
@@ -365,7 +367,7 @@
             other_text.splitlines(True),
             this_text.splitlines(True),
         )
-        m_lines, conflicts = simplemerge.merge_lines(m3, b'OTHER', b'THIS')
+        m_lines, conflicts = simplemerge.render_markers(m3, b'OTHER', b'THIS')
         self.assertEqual(
             b'<<<<<<< OTHER\r\nc\r\n=======\r\nb\r\n'
             b'>>>>>>> THIS\r\n'.splitlines(True),
@@ -381,7 +383,7 @@
             other_text.splitlines(True),
             this_text.splitlines(True),
         )
-        m_lines, conflicts = simplemerge.merge_lines(m3, b'OTHER', b'THIS')
+        m_lines, conflicts = simplemerge.render_markers(m3, b'OTHER', b'THIS')
         self.assertEqual(
             b'<<<<<<< OTHER\rc\r=======\rb\r'
             b'>>>>>>> THIS\r'.splitlines(True),