mercurial/filemerge.py

--- a/mercurial/filemerge.py	Thu Jan 20 13:43:43 2022 -0800
+++ b/mercurial/filemerge.py	Thu Jan 20 14:13:12 2022 -0800
@@ -421,8 +421,6 @@
             )
 
     if premerge:
-        if len(labels) < 3:
-            labels.append(b'base')
         mode = b'merge'
         if premerge == b'keep-mergediff':
             mode = b'mergediff'
@@ -473,14 +471,11 @@
     ui = repo.ui
 
     local = simplemerge.MergeInput(fcd)
-    if len(labels) > 0:
-        local.label = labels[0]
+    local.label = labels[0]
     other = simplemerge.MergeInput(fco)
-    if len(labels) > 1:
-        other.label = labels[1]
+    other.label = labels[1]
     base = simplemerge.MergeInput(fca)
-    if len(labels) > 2:
-        base.label = labels[2]
+    base.label = labels[2]
     r = simplemerge.simplemerge(ui, local, base, other, mode=mode)
     return True, r, False
 
@@ -535,8 +530,6 @@
     files. It will fail if there are any conflicts and leave markers in
     the partially merged file. Marker will have three sections, one from each
     side of the merge and one for the base content."""
-    if len(labels) < 3:
-        labels.append(b'base')
     return _merge(repo, fcd, fco, fca, labels, b'merge3')
 
 
@@ -575,8 +568,6 @@
     the partially merged file. The marker will have two sections, one with the
     content from one side of the merge, and one with a diff from the base
     content to the content on the other side. (experimental)"""
-    if len(labels) < 3:
-        labels.append(b'base')
     return _merge(repo, fcd, fco, fca, labels, b'mergediff')
 
 
@@ -736,10 +727,7 @@
         basepath, otherpath, localoutputpath = temppaths
         outpath = b""
         mylabel, otherlabel = labels[:2]
-        if len(labels) >= 3:
-            baselabel = labels[2]
-        else:
-            baselabel = b'base'
+        baselabel = labels[2]
         env = {
             b'HG_FILE': fcd.path(),
             b'HG_MY_NODE': short(mynode),
@@ -861,9 +849,8 @@
     newlabels = [
         _formatlabel(cd, tmpl, labels[0], pad),
         _formatlabel(co, tmpl, labels[1], pad),
+        _formatlabel(ca, tmpl, labels[2], pad),
     ]
-    if len(labels) > 2:
-        newlabels.append(_formatlabel(ca, tmpl, labels[2], pad))
     return newlabels
 
 
@@ -1063,6 +1050,8 @@
 
     if not labels:
         labels = [b'local', b'other']
+    if len(labels) < 3:
+        labels.append(b'base')
     if mergetype == nomerge:
         return func(repo, mynode, fcd, fco, fca, toolconf, labels)