python: bypass plotnine auto-closing comms

extensions/positron-python/python_files/posit/pinned-test-requirements.txt

@@ -27,6 +27,8 @@ numpy==2.0.2; python_version == '3.9'
 numpy==2.2.4; python_version >= '3.10'
 pandas==2.2.3
 plotly==6.0.1
+plotnine==0.13.6; python_version == '3.9'
+plotnine==0.14.5; python_version >= '3.10'
 polars==1.26.0
 polars[timezone]==1.26.0; sys_platform == 'win32'
 pyarrow==19.0.1

extensions/positron-python/python_files/posit/positron/matplotlib_backend.py

@@ -161,9 +161,11 @@ def render(self, size: PlotSize | None, pixel_ratio: float, format_: str) -> byt
         # Set the device pixel ratio to the requested value.
         self._set_device_pixel_ratio(pixel_ratio)  # type: ignore
 
-        # This must be set before setting the size and can't be passed via print_figure else the
-        # resulting size won't match the request size.
-        self.figure.set_layout_engine("tight")
+        # Check if user has set layout engine for their plot. If layout engine is not "tight",
+        # the resulting size may differ slightly from the request size. However, the layout engine
+        # drastically changes the output, so we should respect the user's choice.
+        if not self.figure.get_layout_engine():
+            self.figure.set_layout_engine("tight")
 
         # Resize the figure to the requested size in pixels.
         if size is None:

extensions/positron-python/python_files/posit/positron/positron_ipkernel.py

@@ -23,6 +23,7 @@
 from ipykernel.zmqshell import ZMQDisplayPublisher, ZMQInteractiveShell
 from IPython.core import magic_arguments, oinspect, page
 from IPython.core.error import UsageError
+from IPython.core.formatters import DisplayFormatter, IPythonDisplayFormatter, catch_format_error
 from IPython.core.interactiveshell import ExecutionInfo, ExecutionResult, InteractiveShell
 from IPython.core.magic import Magics, MagicsManager, line_magic, magics_class
 from IPython.utils import PyColorize
@@ -220,11 +221,34 @@ def connection_show(self, line: str) -> None:
 original_showwarning = warnings.showwarning
 
 
+class PositronDisplayFormatter(DisplayFormatter):
+    @traitlets.default("ipython_display_formatter")
+    def _default_formatter(self):
+        return PositronIPythonDisplayFormatter(parent=self)
+
+
+class PositronIPythonDisplayFormatter(IPythonDisplayFormatter):
+    print_method = traitlets.ObjectName("_ipython_display_")
+    _return_type = (type(None), bool)
+
+    @catch_format_error
+    def __call__(self, obj):
+        """Compute the format for an object."""
+        try:
+            if obj.__module__ == "plotnine.ggplot":
+                obj.draw(show=True)
+                return True
+        except AttributeError:
+            pass
+        return super().__call__(obj)
+
+
 class PositronShell(ZMQInteractiveShell):
     kernel: PositronIPyKernel
     object_info_string_level: int
     magics_manager: MagicsManager
     display_pub: ZMQDisplayPublisher
+    display_formatter: PositronDisplayFormatter = traitlets.Instance(PositronDisplayFormatter)  # type: ignore
 
     inspector_class: type[PositronIPythonInspector] = traitlets.Type(
         PositronIPythonInspector,  # type: ignore
@@ -296,6 +320,10 @@ def init_user_ns(self):
             }
         )
 
+    def init_display_formatter(self):
+        self.display_formatter = PositronDisplayFormatter(parent=self)
+        self.configurables.append(self.display_formatter)  # type: ignore IPython type annotation is wrong
+
     def _handle_pre_run_cell(self, info: ExecutionInfo) -> None:
         """Prior to execution, reset the user environment watch state."""
         # If an empty cell is being executed, do nothing.

extensions/positron-python/python_files/posit/positron/tests/test_plots.py

@@ -350,3 +350,25 @@ def test_mpl_shutdown(shell: PositronShell, plots_service: PlotsService) -> None
     # Plots are closed and cleared.
     assert not plots_service._plots  # noqa: SLF001
     assert all(comm._closed for comm in plot_comms)  # noqa: SLF001
+
+
+def test_plotnine_close_then_show(shell: PositronShell, plots_service: PlotsService) -> None:
+    """Test that a plotnine plot renders and then closes comm correctly."""
+    shell.run_cell("""\
+from plotnine import ggplot, geom_point, aes, stat_smooth, facet_wrap
+from plotnine.data import mtcars
+
+(
+    ggplot(mtcars, aes("wt", "mpg", color="factor(gear)"))
+    + geom_point()
+    + stat_smooth(method="lm")
+    + facet_wrap("gear")
+)\
+""").raise_error()
+    plot_comm = cast("DummyComm", plots_service._plots[0]._comm.comm)  # noqa: SLF001
+
+    assert plot_comm.messages == [
+        comm_open_message(_CommTarget.Plot),
+        json_rpc_notification("show", {}),
+    ]
+    assert not plot_comm._closed  # noqa: SLF001

extensions/positron-python/python_files/posit/test-requirements.txt

@@ -12,6 +12,7 @@ matplotlib
 numpy
 pandas
 plotly
+plotnine
 polars
 polars[timezone]; sys_platform == 'win32'
 pyarrow