ci: add pyodide build

[henryiii]

Testing this.

[henryiii]

This is the only failing part, don't know if it's directly pyodide's fault:

  ______________________ test_NormalConstraint_bad_input_4 _______________________
      def test_NormalConstraint_bad_input_4():
  >       with pytest.raises(ValueError, match="positive definite"):
  E       Failed: DID NOT RAISE <class 'ValueError'>
  /home/runner/work/iminuit/iminuit/tests/test_cost.py:1573: Failed
  ______________________ test_NormalConstraint_bad_input_5 _______________________
      def test_NormalConstraint_bad_input_5():
          n = NormalConstraint(["a", "b"], [1, 2], [[1, 0], [0, 1]])
      
  >       with pytest.raises(ValueError, match="positive definite"):
  E       Failed: DID NOT RAISE <class 'ValueError'>
  /home/runner/work/iminuit/iminuit/tests/test_cost.py:1580: Failed
  ____________________________ test_positive_definite ____________________________
      def test_positive_definite():
          assert util.is_positive_definite([[1, 0], [0, 1]])
  >       assert not util.is_positive_definite([[1, 1], [1, 1]])
  E       assert not True
  E        +  where True = <function is_positive_definite at 0x2898118>([[1, 1], [1, 1]])
  E        +    where <function is_positive_definite at 0x2898118> = util.is_positive_definite
  /home/runner/work/iminuit/iminuit/tests/test_util.py:776: AssertionError

[HDembinski]

This is the only failing part, don't know if it's directly pyodide's fault:

  ______________________ test_NormalConstraint_bad_input_4 _______________________
      def test_NormalConstraint_bad_input_4():
  >       with pytest.raises(ValueError, match="positive definite"):
  E       Failed: DID NOT RAISE <class 'ValueError'>
  /home/runner/work/iminuit/iminuit/tests/test_cost.py:1573: Failed
  ______________________ test_NormalConstraint_bad_input_5 _______________________
      def test_NormalConstraint_bad_input_5():
          n = NormalConstraint(["a", "b"], [1, 2], [[1, 0], [0, 1]])
      
  >       with pytest.raises(ValueError, match="positive definite"):
  E       Failed: DID NOT RAISE <class 'ValueError'>
  /home/runner/work/iminuit/iminuit/tests/test_cost.py:1580: Failed
  ____________________________ test_positive_definite ____________________________
      def test_positive_definite():
          assert util.is_positive_definite([[1, 0], [0, 1]])
  >       assert not util.is_positive_definite([[1, 1], [1, 1]])
  E       assert not True
  E        +  where True = <function is_positive_definite at 0x2898118>([[1, 1], [1, 1]])
  E        +    where <function is_positive_definite at 0x2898118> = util.is_positive_definite
  /home/runner/work/iminuit/iminuit/tests/test_util.py:776: AssertionError

The two errors seem related to util.is_positive_definite, which is implemented as follows:

    m = np.atleast_2d(m)
    if np.all(m.T == m):
        # maybe check this first https://en.wikipedia.org/wiki/Diagonally_dominant_matrix
        # and only try cholesky if that fails
        try:
            np.linalg.cholesky(m)
        except np.linalg.LinAlgError:
            return False
        return True
    return False

This returns true in those failing cases although it should return false. Apparently, np.linalg.cholesky(m) is not raising LinAlgError on Pyiodide.

[HDembinski]

Perhaps the line np.linalg.cholesky(m) is non-blocking in Pyiodide. This code assumes it is blocking, like any other normal Python statement.

[henryiii]

I bet NumPy is compiled with exceptions turned off; maybe this function actually raises the exception from the compiled code?

I'll look into this and report to pyodide with what I find. The snippet above is extremely helpful, thank you!

[HDembinski]

@henryiii I made a patch which may work around the failing test in pyodide, but I cannot test it because the pyodide build now fails because of some build-system issue. I am closing this PR now, you can reopen it when you find the time to finish this.