windows: disable pager when packaged with py2exe

With Windows and py3, all output that got directed to the pager was lost.  It
can be worked around by the user piping to `more`, but that's easy to forget,
and can be dangerous if `hg diff` or similar incorrectly shows no changes.  The
problem appears to be the new WindowsConsoleIO in py3.6[1].  We've worked around
it with PyOxidizer by setting the `Py_LegacyWindowsStdioFlag` interpreter
option, and worked around it with `hg.bat` and `exewrapper.c` by internally
setting `PYTHONLEGACYWINDOWSSTDIO=1`.

Unfortunately, py2exe doesn't appear to be able to set the interpreter option,
and somehow seems to also ignore the environment variable.  The latter isn't a
good fix anyway, since setting it in the environment would affect other python
programs too.  We can't install a global config for this because a config closer
to the user (e.g. from before pager was turned on by default) can override it.

[1] https://peps.python.org/pep-0528/

Differential Revision: https://phab.mercurial-scm.org/D12556

mercurial/ui.py

@@ -1432,6 +1432,14 b' class ui:'
             # HGPLAINEXCEPT=pager, and the user didn't specify --debug.
             return
 
+        # py2exe doesn't appear to be able to use legacy I/O, and nothing is
+        # output to the pager for paged commands.  Piping to `more` in cmd.exe
+        # works, but is easy to forget.  Just disable pager for py2exe, but
+        # leave it working for pyoxidizer and exewrapper builds.
+        if pycompat.iswindows and getattr(sys, "frozen", None) == "console_exe":
+            self.debug(b"pager is unavailable with py2exe packaging\n")
+            return
+
         pagercmd = self.config(b'pager', b'pager', rcutil.fallbackpager)
         if not pagercmd:
             return