--- a/mercurial/exchange.py	Sat Feb 29 12:58:13 2020 +0530
+++ b/mercurial/exchange.py	Sat Feb 29 12:58:38 2020 +0530
@@ -8,6 +8,7 @@
 from __future__ import absolute_import
 
 import collections
+import weakref
 
 from .i18n import _
 from .node import (
@@ -1705,6 +1706,25 @@
         pullop.rheads = set(pullop.rheads) - pullop.common
 
 
+def add_confirm_callback(repo, pullop):
+    """ adds a finalize callback to transaction which can be used to show stats
+    to user and confirm the pull before committing transaction """
+
+    tr = pullop.trmanager.transaction()
+    scmutil.registersummarycallback(
+        repo, tr, txnname=b'pull', as_validator=True
+    )
+    reporef = weakref.ref(repo.unfiltered())
+
+    def prompt(tr):
+        repo = reporef()
+        cm = _(b'accept incoming changes (yn)?$$ &Yes $$ &No')
+        if repo.ui.promptchoice(cm):
+            raise error.Abort("user aborted")
+
+    tr.addvalidator(b'900-pull-prompt', prompt)
+
+
 def pull(
     repo,
     remote,
@@ -1716,6 +1736,7 @@
     includepats=None,
     excludepats=None,
     depth=None,
+    confirm=None,
 ):
     """Fetch repository data from a remote.
 
@@ -1740,6 +1761,8 @@
     ``depth`` is an integer indicating the DAG depth of history we're
     interested in. If defined, for each revision specified in ``heads``, we
     will fetch up to this many of its ancestors and data associated with them.
+    ``confirm`` is a boolean indicating whether the pull should be confirmed
+    before committing the transaction. This overrides HGPLAIN.
 
     Returns the ``pulloperation`` created for this pull.
     """
@@ -1786,6 +1809,11 @@
     if not bookmod.bookmarksinstore(repo):
         wlock = repo.wlock()
     with wlock, repo.lock(), pullop.trmanager:
+        if confirm or (
+            repo.ui.configbool(b"pull", b"confirm") and not repo.ui.plain()
+        ):
+            add_confirm_callback(repo, pullop)
+
         # Use the modern wire protocol, if available.
         if remote.capable(b'command-changesetdata'):
             exchangev2.pull(pullop)