Raise ValueError when trying to create PhaseDiagram without entries

[peikai]

I committed some codes to raise a specific ValueError exception and hint a specific reason message for the attempt to build a phase diagram with no entries. A corresponding unittest was also added.

Scenario:
In the cases that there are not enough entries to form a complete phase diagram, the processing operation of the mixing scheme would fail and might return an empty list, i.e., entryList = []. That would cause an error in PhaseDiagram class when computing data, as shown below. To raise a specific exception is necessary.

Run:

entryList = MaterialsProjectDFTMixingScheme().process_entries(entryList, clean=True)
phase_diagram = PhaseDiagram(entryList)

Errors:

Generating mixing state data from provided entries.
D:\Anaconda\envs\pymatgen2023\Lib\site-packages\pymatgen\entries\mixing_scheme.py:508: UserWarning: GGA(+U) entries do not form a complete PhaseDiagram.
warnings.warn(f"{self.run_type_1} entries do not form a complete PhaseDiagram.")
Entries contain R2SCAN calculations for 0 of 0 GGA(+U) hull entries.
GGA(+U) energies will be adjusted to the R2SCAN scale
D:\Anaconda\envs\pymatgen2023\Lib\site-packages\pymatgen\entries\mixing_scheme.py:215: UserWarning: WARNING! GGA(+U) entries do not form a complete PhaseDiagram. No energy adjustments will be applied.
warnings.warn(str(exc))
Processing complete. Mixed entries contain 0 GGA(+U) and 0 R2SCAN entries.

Traceback (most recent call last):
phase_diagram = PhaseDiagram(entryList)
^^^^^^^^^^^^^^^^^^^^^^^
File "D:\Anaconda\envs\pymatgen2023\Lib\site-packages\pymatgen\analysis\phase_diagram.py", line 366, in init
computed_data = self._compute()
^^^^^^^^^^^^^^^
File "D:\Anaconda\envs\pymatgen2023\Lib\site-packages\pymatgen\analysis\phase_diagram.py", line 445, in _compute
form_e = -np.dot(data, vec)
^^^^^^^^^^^^^^^^^
File "<array_function internals>", line 180, in dot
ValueError: shapes (0,) and (1,) not aligned: 0 (dim 0) != 1 (dim 0)

[coveralls]

Coverage: 78.165% (-0.7%) from 78.875% when pulling a047696 on peikai:EmptyEntryList into ef98f0b on materialsproject:master.

[janosh]

Thanks @peikai! 👍

[peikai]

Great!