refactor the dodiff optimization

mercurial/commands.py

@@ -276,12 +276,13 b' def make_file(repo, r, pat, node=None,'
 
 def dodiff(fp, ui, repo, node1, node2, files=None, match=util.always,
            changes=None, text=False, opts={}):
-    if node1:
-        # reading the data for node1 early allows it to play nicely
-        # with repo.changes and the revlog cache.
-        change = repo.changelog.read(node1)
-        mmap = repo.manifest.read(change[0])
-        date1 = util.datestr(change[2])
+    if not node1:
+        node1 = repo.dirstate.parents()[0]
+    # reading the data for node1 early allows it to play nicely
+    # with repo.changes and the revlog cache.
+    change = repo.changelog.read(node1)
+    mmap = repo.manifest.read(change[0])
+    date1 = util.datestr(change[2])
 
     if not changes:
         changes = repo.changes(node1, node2, files, match=match)
@@ -301,11 +302,6 b' def dodiff(fp, ui, repo, node1, node2, f'
             return repo.file(f).read(mmap2[f])
     else:
         date2 = util.datestr()
-        if not node1:
-            node1 = repo.dirstate.parents()[0]
-            change = repo.changelog.read(node1)
-            mmap = repo.manifest.read(change[0])
-            date1 = util.datestr(change[2])
         def read(f):
             return repo.wread(f)