bpo-37627: Initialize IDLE Custom Run dialog with previous entries (#14870)

Repeat the command line arguments most recently entered before so the user can edit them.
diff --git a/Lib/idlelib/idle_test/test_query.py b/Lib/idlelib/idle_test/test_query.py
index 3b444de..f957585 100644
--- a/Lib/idlelib/idle_test/test_query.py
+++ b/Lib/idlelib/idle_test/test_query.py
@@ -12,7 +12,7 @@
 from idlelib import query
 import unittest
 from test.support import requires
-from tkinter import Tk
+from tkinter import Tk, END
 
 import sys
 from unittest import mock
@@ -392,10 +392,12 @@
     def test_click_args(self):
         root = Tk()
         root.withdraw()
-        dialog =  query.CustomRun(root, 'Title', _utest=True)
-        dialog.entry.insert(0, 'okay')
+        dialog =  query.CustomRun(root, 'Title',
+                                  cli_args=['a', 'b=1'], _utest=True)
+        self.assertEqual(dialog.entry.get(), 'a b=1')
+        dialog.entry.insert(END, ' c')
         dialog.button_ok.invoke()
-        self.assertEqual(dialog.result, (['okay'], True))
+        self.assertEqual(dialog.result, (['a', 'b=1', 'c'], True))
         root.destroy()
 
 
diff --git a/Lib/idlelib/query.py b/Lib/idlelib/query.py
index d74084f..097e6e6 100644
--- a/Lib/idlelib/query.py
+++ b/Lib/idlelib/query.py
@@ -325,9 +325,13 @@
     """
     # Used in runscript.run_custom_event
 
-    def __init__(self, parent, title, *, cli_args='',
+    def __init__(self, parent, title, *, cli_args=[],
                  _htest=False, _utest=False):
-        # TODO Use cli_args to pre-populate entry.
+        """cli_args is a list of strings.
+
+        The list is assigned to the default Entry StringVar.
+        The strings are displayed joined by ' ' for display.
+        """
         message = 'Command Line Arguments for sys.argv:'
         super().__init__(
                 parent, title, message, text0=cli_args,
diff --git a/Lib/idlelib/runscript.py b/Lib/idlelib/runscript.py
index b041e56..f97cf52 100644
--- a/Lib/idlelib/runscript.py
+++ b/Lib/idlelib/runscript.py
@@ -39,6 +39,8 @@
         # XXX This should be done differently
         self.flist = self.editwin.flist
         self.root = self.editwin.root
+        # cli_args is list of strings that extends sys.argv
+        self.cli_args = []
 
         if macosx.isCocoaTk():
             self.editwin.text_frame.bind('<<run-module-event-2>>', self._run_module_event)
@@ -137,10 +139,11 @@
             return 'break'
         if customize:
             title = f"Customize {self.editwin.short_title()} Run"
-            run_args = CustomRun(self.shell.text, title).result
+            run_args = CustomRun(self.shell.text, title,
+                                 cli_args=self.cli_args).result
             if not run_args:  # User cancelled.
                 return 'break'
-        cli_args, restart = run_args if customize else ([], True)
+        self.cli_args, restart = run_args if customize else ([], True)
         interp = self.shell.interp
         if pyshell.use_subprocess and restart:
             interp.restart_subprocess(
@@ -148,8 +151,8 @@
                     self.editwin._filename_to_unicode(filename))
         dirname = os.path.dirname(filename)
         argv = [filename]
-        if cli_args:
-            argv += cli_args
+        if self.cli_args:
+            argv += self.cli_args
         interp.runcommand(f"""if 1:
             __file__ = {filename!r}
             import sys as _sys