Move papersize="auto" deprecation to backend_bases.

This makes it easier for mplcairo (which also outputs PostScript
natively) to inherit the deprecation and be able to run the matplotlib
test suite both with matplotlib 3.7 (where there should be no warning)
and with matplotlib 3.8 (where there should be a warning).

Author: anntzer

lib/matplotlib/backend_bases.py

@@ -2105,6 +2105,12 @@ def print_figure(
         if dpi == 'figure':
             dpi = getattr(self.figure, '_original_dpi', self.figure.dpi)
 
+        if kwargs.get("papertype") == 'auto':
+            # When deprecation elapses, remove backend_ps._get_papertype & its callers.
+            _api.warn_deprecated(
+                "3.8", name="papertype='auto'", addendum="Pass an explicit paper type, "
+                "'figure', or omit the *papertype* argument entirely.")
+
         # Remove the figure manager, if any, to avoid resizing the GUI widget.
         with cbook._setattr_cm(self, manager=None), \
              self._switch_canvas_and_return_print_method(format, backend) \

lib/matplotlib/backends/backend_ps.py

@@ -867,9 +867,6 @@ def _print_figure(
         # find the appropriate papertype
         width, height = self.figure.get_size_inches()
         if papertype == 'auto':
-            _api.warn_deprecated("3.8", name="papertype='auto'",
-                                 addendum="Pass an explicit paper type, 'figure', or "
-                                 "omit the *papertype* argument entirely.")
             papertype = _get_papertype(*orientation.swap_if_landscape((width, height)))
 
         if is_eps or papertype == 'figure':
@@ -1053,9 +1050,6 @@ def _print_figure_tex(
                     self.figure.get_size_inches())
             else:
                 if papertype == 'auto':
-                    _api.warn_deprecated("3.8", name="papertype='auto'",
-                                         addendum="Pass an explicit paper type, or "
-                                         "omit the *papertype* argument entirely.")
                     papertype = _get_papertype(width, height)
                 paper_width, paper_height = papersize[papertype]