--- a/mercurial/cext/parsers.c	Sat Jul 03 04:07:21 2021 +0200
+++ b/mercurial/cext/parsers.c	Sat Jul 03 04:26:28 2021 +0200
@@ -29,6 +29,8 @@
 
 static const char *const versionerrortext = "Python minor version mismatch";
 
+static const int dirstate_v1_from_p2 = -2;
+
 static PyObject *dict_new_presized(PyObject *self, PyObject *args)
 {
 	Py_ssize_t expected_size;
@@ -164,9 +166,19 @@
 	}
 };
 
+static PyObject *dirstatetuple_get_from_p2(dirstateTupleObject *self)
+{
+	if (self->size == dirstate_v1_from_p2) {
+		Py_RETURN_TRUE;
+	} else {
+		Py_RETURN_FALSE;
+	}
+};
+
 static PyGetSetDef dirstatetuple_getset[] = {
     {"state", (getter)dirstatetuple_get_state, NULL, "state", NULL},
     {"merged", (getter)dirstatetuple_get_merged, NULL, "merged", NULL},
+    {"from_p2", (getter)dirstatetuple_get_from_p2, NULL, "from_p2", NULL},
     {NULL} /* Sentinel */
 };
 

--- a/mercurial/dirstate.py	Sat Jul 03 04:07:21 2021 +0200
+++ b/mercurial/dirstate.py	Sat Jul 03 04:26:28 2021 +0200
@@ -393,7 +393,7 @@
                         copies[f] = source
                     self.normallookup(f)
                 # Also fix up otherparent markers
-                elif s.state == b'n' and s[2] == FROM_P2:
+                elif s.state == b'n' and s.from_p2:
                     source = self._map.copymap.get(f)
                     if source:
                         copies[f] = source
@@ -531,16 +531,18 @@
             # being removed, restore that state.
             entry = self._map.get(f)
             if entry is not None:
-                if entry.state == b'r' and entry[2] in (NONNORMAL, FROM_P2):
+                if entry.state == b'r' and (
+                    entry[2] == NONNORMAL or entry.from_p2
+                ):
                     source = self._map.copymap.get(f)
                     if entry[2] == NONNORMAL:
                         self.merge(f)
-                    elif entry[2] == FROM_P2:
+                    elif entry.from_p2:
                         self.otherparent(f)
                     if source:
                         self.copy(source, f)
                     return
-                if entry.merged or entry.state == b'n' and entry[2] == FROM_P2:
+                if entry.merged or entry.state == b'n' and entry.from_p2:
                     return
         self._addpath(f, b'n', 0, possibly_dirty=True)
         self._map.copymap.pop(f, None)
@@ -1336,7 +1338,7 @@
                         (size != st.st_size and size != st.st_size & _rangemask)
                         or ((mode ^ st.st_mode) & 0o100 and checkexec)
                     )
-                    or size == FROM_P2  # other parent
+                    or t.from_p2
                     or fn in copymap
                 ):
                     if stat.S_ISLNK(st.st_mode) and size != st.st_size:

--- a/mercurial/dirstatemap.py	Sat Jul 03 04:07:21 2021 +0200
+++ b/mercurial/dirstatemap.py	Sat Jul 03 04:26:28 2021 +0200
@@ -173,7 +173,7 @@
                 # backup the previous state
                 if entry.merged:  # merge
                     size = NONNORMAL
-                elif entry[0] == b'n' and entry[2] == FROM_P2:  # other parent
+                elif entry[0] == b'n' and entry.from_p2:
                     size = FROM_P2
                     self.otherparentset.add(f)
         if size == 0:

--- a/mercurial/pure/parsers.py	Sat Jul 03 04:07:21 2021 +0200
+++ b/mercurial/pure/parsers.py	Sat Jul 03 04:26:28 2021 +0200
@@ -33,6 +33,10 @@
 _decompress = zlib.decompress
 
 
+# a special value used internally for `size` if the file come from the other parent
+FROM_P2 = -2
+
+
 class dirstatetuple(object):
     """represent a dirstate entry
 
@@ -87,6 +91,14 @@
         """
         return self._state == b'm'
 
+    @property
+    def from_p2(self):
+        """True if the file have been fetched from p2 during the current merge
+
+        Should only be set if a merge is in progress in the dirstate
+        """
+        return self._size == FROM_P2
+
     def v1_state(self):
         """return a "state" suitable for v1 serialization"""
         return self._state