debugshell: allow commands to be specified as a CLI argument Add a `--command` option to `hg debugshell` that allows the user to pass in Python code to evaluate directly from the command line. This was inspired by the `--command` option present in Facebook's Sapling fork of Mercurial, which in turn was inspired by the `-c` option of the Python interpreter itself. It is particularly useful for writing tests, especially for getting visibility into things that otherwise aren't exposed via debug commands.

--- a/tests/test-debugcommands.t	Tue Jan 10 11:40:19 2023 +0100
+++ b/tests/test-debugcommands.t	Thu Jan 19 11:12:20 2023 -0500
@@ -724,3 +724,8 @@
   pushable: yes
 
 #endif
+
+Test debugshell
+
+  $ hg debugshell -c 'ui.write(b"%s\n" % ui.username())'
+  test