FIX: pcolormesh writing to read-only input mask

Author: Yi Wei

lib/matplotlib/axes/_axes.py

@@ -5764,7 +5764,7 @@ def _pcolorargs(self, funcname, *args, shading='auto', **kwargs):
             else:
                 X, Y = np.meshgrid(np.arange(ncols + 1), np.arange(nrows + 1))
                 shading = 'flat'
-            C = cbook.safe_masked_invalid(C)
+            C = cbook.safe_masked_invalid(C, copy=True)
             return X, Y, C, shading
 
         if len(args) == 3:
@@ -5853,7 +5853,7 @@ def _interp_grid(X):
                     Y = _interp_grid(Y.T).T
                 shading = 'flat'
 
-        C = cbook.safe_masked_invalid(C)
+        C = cbook.safe_masked_invalid(C, copy=True)
         return X, Y, C, shading
 
     @_preprocess_data()

lib/matplotlib/cbook.py

@@ -668,7 +668,7 @@ def remove(self, o):
                 self.push(elem)
 
 
-def safe_masked_invalid(x, copy=True):
+def safe_masked_invalid(x, copy=False):
     x = np.array(x, subok=True, copy=copy)
     if not x.dtype.isnative:
         # If we have already made a copy, do the byteswap in place, else make a