Fix dotplot size legend layout issue (overlapping circles) without changing DEFAULT_LEGENDS_WIDTH

- Reverts the change to the global DotPlot.DEFAULT_LEGENDS_WIDTH meant to fix layout issue with overlapping circles in the size legend under certain conditions (especially when dendrogram = True).

- The legend width is now adjusted locally within the dotplot wrapper function.

- This avoids unintended layout changes to other plots and minimizes the number of test images that need to be updated.

Author: rwbaber

src/scanpy/plotting/_dotplot.py

@@ -108,7 +108,7 @@ class DotPlot(BasePlot):
     # default legend parameters
     DEFAULT_SIZE_LEGEND_TITLE = "Fraction of cells\nin group (%)"
     DEFAULT_COLOR_LEGEND_TITLE = "Mean expression\nin group"
-    DEFAULT_LEGENDS_WIDTH = 1.7  # inches
+    DEFAULT_LEGENDS_WIDTH = 1.5  # inches
     DEFAULT_PLOT_X_PADDING = 0.8  # a unit is the distance between two x-axis ticks
     DEFAULT_PLOT_Y_PADDING = 1.0  # a unit is the distance between two y-axis ticks
 
@@ -559,7 +559,7 @@ def _plot_size_legend(self, size_legend_ax: Axes):
         size_legend_ax.set_title(self.size_title, y=ymax + 0.45, size="small")
 
         xmin, xmax = size_legend_ax.get_xlim()
-        size_legend_ax.set_xlim(xmin - 0.15, xmax + 0.25)
+        size_legend_ax.set_xlim(xmin - 0.15, xmax + 0.5)
 
     def _plot_legend(self, legend_ax, return_ax_dict, normalize):
         # to maintain the fixed height size of the legends, a
@@ -630,15 +630,20 @@ def _plot_stacked_colorbars(self, fig, colorbar_area_spec, normalize):
         n_cbars = len(groups_to_plot)
 
         # Create a sub-grid just for the colorbars
-        colorbar_gs = colorbar_area_spec.subgridspec(n_cbars, 1, hspace=0.6)
+        # Create an empty column to keep colorbars at 3/4 of legend width (1.5 like default with dp.legend_width = 2.0)
+        colorbar_gs = colorbar_area_spec.subgridspec(
+            n_cbars, 2, hspace=0.6, width_ratios=[3, 1]
+        )
 
         # Create a dedicated normalizer for the legend
         vmin = self.dot_color_df.values.min()
         vmax = self.dot_color_df.values.max()
         legend_norm = mpl.colors.Normalize(vmin=vmin, vmax=vmax)
 
         for i, group_name in enumerate(groups_to_plot):
-            ax = fig.add_subplot(colorbar_gs[i])
+            ax = fig.add_subplot(
+                colorbar_gs[i, 0]
+            )  # Place the colorbar Axes in the first, wider column
             cmap = colormaps.get_cmap(self.group_cmaps[group_name])
             mappable = ScalarMappable(norm=legend_norm, cmap=cmap)
 
@@ -1163,7 +1168,9 @@ def dotplot(  # noqa: PLR0913
         dot_min=dot_min,
         smallest_dot=smallest_dot,
         dot_edge_lw=kwds.pop("linewidth", _empty),
-    ).legend(colorbar_title=colorbar_title, size_title=size_title)
+    ).legend(
+        colorbar_title=colorbar_title, size_title=size_title, width=2.0
+    )  # Width 2.0 to avoid size legend circles to overlap
 
     if return_fig:
         return dp