histedit: preserve initial author on fold (issue4296)

When the authorship of the changeset folded in does not match that of
the base changeset, we currently use the configured ui.username
instead. This is especially surprising when the user is not the author
of either of the changesets. In such cases, the resulting authorship
(the user's) is clearly incorrect. Even when the user is folding in a
patch they authored themselves, it's not clear whether they should
take over the authorship. Let's instead keep it simple and always
preserve the base changeset's authorship. This is also how
"git rebase -i" handles folding/squashing.

hgext/histedit.py

@@ -354,12 +354,7 b' def finishfold(ui, repo, ctx, oldctx, ne'
     hg.update(repo, parent)
     ### prepare new commit data
     commitopts = opts.copy()
-    # username
-    if ctx.user() == oldctx.user():
-        username = ctx.user()
-    else:
-        username = ui.username()
-    commitopts['user'] = username
+    commitopts['user'] = ctx.user()
     # commit message
     newmessage = '\n***\n'.join(
         [ctx.description()] +

tests/test-histedit-fold.t

@@ -169,6 +169,44 b' check saving last-message.txt'
   check saving last-message.txt
 
   $ cd ..
+  $ rm -r r
+
+folding preserves initial author
+--------------------------------
+
+  $ initrepo
+
+  $ hg ci --user "someone else" --amend --quiet
+
+tip before edit
+  $ hg log --rev .
+  changeset:   5:a00ad806cb55
+  tag:         tip
+  user:        someone else
+  date:        Thu Jan 01 00:00:00 1970 +0000
+  summary:     f
+  
+
+  $ hg histedit e860deea161a --commands - 2>&1 <<EOF | fixbundle
+  > pick e860deea161a e
+  > fold a00ad806cb55 f
+  > EOF
+  0 files updated, 0 files merged, 1 files removed, 0 files unresolved
+  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
+  2 files updated, 0 files merged, 0 files removed, 0 files unresolved
+  0 files updated, 0 files merged, 0 files removed, 0 files unresolved
+
+tip after edit
+  $ hg log --rev .
+  changeset:   4:698d4e8040a1
+  tag:         tip
+  user:        test
+  date:        Thu Jan 01 00:00:00 1970 +0000
+  summary:     e
+  
+
+  $ cd ..
+  $ rm -r r
 
 folding and creating no new change doesn't break:
 -------------------------------------------------