fix: norm and vmin/vmax in raster.py (#6889)

Author: JulianGiles

holoviews/plotting/mpl/raster.py

@@ -216,11 +216,11 @@ def get_data(self, element, ranges, style):
 
     def init_artists(self, ax, plot_args, plot_kwargs):
         locs = plot_kwargs.pop("locs", None)
-        artist = ax.pcolormesh(*plot_args, **plot_kwargs)
-        colorbar = self.handles.get("cbar")
         if "norm" in plot_kwargs:  # vmin/vmax should now be exclusively in norm
             plot_kwargs.pop("vmin", None)
             plot_kwargs.pop("vmax", None)
+        artist = ax.pcolormesh(*plot_args, **plot_kwargs)
+        colorbar = self.handles.get("cbar")
         if colorbar and MPL_VERSION < (3, 1, 0):
             colorbar.set_norm(artist.norm)
             if hasattr(colorbar, "set_array"):

holoviews/tests/plotting/matplotlib/test_quadmeshplot.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 import numpy as np
+from matplotlib.colors import Normalize
 
 import holoviews as hv
 
@@ -57,3 +58,16 @@ def test_quadmesh_update_cbar(self):
         np.testing.assert_allclose(
             [cbar.vmin, cbar.vmax], [-1.7481711049213744, 1.7008913273857975]
         )
+
+    def test_quadmesh_with_norm(self):
+        arr = np.array([[0, 1, 2], [3, 4, 5]])
+
+        qmesh = hv.QuadMesh(hv.Image(arr)).opts(norm=Normalize(), cmap="viridis")
+
+        # Before PR 6889, getting the plot would raise a ValueError from
+        # matplotlib because vmin and vmax were passed alongside the norm.
+        plot = mpl_renderer.get_plot(qmesh)
+
+        # Verify the plot handles were created and the norm is correctly applied
+        artist = plot.handles["artist"]
+        assert isinstance(artist.norm, Normalize)