revert: ask user to confirm before tracking new file when interactive

If interactively reverting from a commit with `hg revert -i -r`, we
would unconditionally add files from that commit that are not already
tracked in the working copy. We have prompts for adding back files
removed in the working copy, but that's specific to such files and
does not apply to adding files from another revision.

Differential Revision: https://phab.mercurial-scm.org/D12416

mercurial/cmdutil.py

@@ -3752,6 +3752,12 b' def _performrevert('
         if f in newlyaddedandmodifiedfiles:
             continue
 
+        if interactive:
+            choice = repo.ui.promptchoice(
+                _(b"add new file %s (Yn)?$$ &Yes $$ &No") % uipathfn(f)
+            )
+            if choice != 0:
+                continue
         prntstatusmsg(b'add', f)
         checkout(f)
         repo.dirstate.set_tracked(f)

tests/test-revert-interactive.t

@@ -420,6 +420,19 b' 3) Use interactive revert with editing ('
   forgetting newfile
   $ hg status
   ? newfile
+  $ rm newfile
+  $ hg up 0
+  1 files updated, 0 files merged, 4 files removed, 0 files unresolved
+  $ hg status
+  $ hg revert -r 2 -i <<EOF
+  > y
+  > n
+  > EOF
+  add new file folder1/g (Yn)? y
+  adding folder1/g
+  add new file folder2/h (Yn)? n
+  $ hg status
+  A folder1/g
 
 When a line without EOL is selected during "revert -i" (issue5651)