show_mpl Bands plot failure

[mikeatm]

When plotting BandsData, the distance computation does not take into account when all the high symmetry points have a label in self.labels, https://github.com/aiidateam/aiida-core/blob/bab1ad6cfc8e4ff041bce268f9270c613663cb35/aiida/orm/nodes/data/array/bands.py#L477-L481 which leads to a situation where, if you label all the high symmetry points, then all the distances are set to zero, and the x coordinates now are all set to zero https://github.com/aiidateam/aiida-core/blob/bab1ad6cfc8e4ff041bce268f9270c613663cb35/aiida/orm/nodes/data/array/bands.py#L482 Here is some info:

In [34]: bs.get_kpoints()
Out[34]: 
array([[0. , 0. , 0. ],
       [0. , 0.5, 0. ],
       [0.5, 0.5, 0. ],
       [0. , 0. , 0. ],
       [0.5, 0.5, 0.5],
       [0. , 0.5, 0. ],
       [0.5, 0.5, 0.5],
       [0.5, 0.5, 0. ]])

In [35]: bs.labels= [(0, 'GAMMA'), (1,'X'), (2,'M'),(3,'GAMMA'),(4,'R'),(5,'X'),(6,'R'),(7,'M')]

In [36]: bs._get_bandplot_data(cartesian=True,  prettify_format=None, join_symbol=None, get_segments=False)
Out[36]: 
{'x': [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0],   ## ******************ALL THIS*************************
 'y': array([[-31.70204001, -31.64247329, -31.64247308, ...,  57.5809345 ,
          58.10566081,  59.20231692],
        [-31.68186564, -31.66189384, -31.64213932, ...,  58.28154109,
          58.62465083,  58.62469309],
        [-31.66192103, -31.66170643, -31.66170595, ...,  56.1907462 ,
          56.68984233,  56.72449097],
        ...,

and when there is no labels:

In [37]: bs.labels= []

In [38]: bs._get_bandplot_data(cartesian=True,  prettify_format=None, join_symbol=None, get_segments=False)
Out[38]: 
{'x': [0.0,                          # *******************ALL THIS************************
  0.5000000021868258,
  1.0000000043736517,
  1.707106788652838,
  2.57313219622497,
  3.280238980504156,
  3.987345764783342,
  4.487345766970168],
 'y': array([[-31.70204001, -31.64247329, -31.64247308, ...,  57.5809345 ,
          58.10566081,  59.20231692],
        [-31.68186564, -31.66189384, -31.64213932, ...,  58.28154109,
          58.62465083,  58.62469309],
        [-31.66192103, -31.66170643, -31.66170595, ...,  56.1907462 ,
          56.68984233,  56.72449097],
        ...,

This of course means that the plotting fails.