MAINT: spatial: Explicitly initialize LAPACK output parameters.

[tpudlik]

Prior to this PR, the info and rcond parameters were not initialized in the .pyx file (and so not in the generated C code). The SciPy code relied on the invoked LAPACK routines to initialize these parameters.

However, it is not guaranteed that the LAPACK routines will perform the initialization. For example, dgecon may return before initializing rcond; the Clang MemorySanitizer flags the subsequent use of this variable (line 1124) as use-of-uninitialized-value. Fortunately, in this case there is no bug in behavior, because the LAPACK routine only fails to initialize rcond if it sets info to a nonzero value. The end result is that _get_barycentric_transforms is guaranteed to return a matrix of NaNs in that case, even though the truth value of the if-statement condition is undefined. Still, comparisons involving undefined values make the code needlessly fragile.

[tylerjereddy]

Looks pretty subtle; the CI test failures don't appear to be directly related, but I'll have to take a closer look.

If there's no actual bug I suppose writing a unit test to prevent "regression" would be tricky.

@pv is the author of the module & can perhaps comment

[ilayn]

Note that the first of the mentioned info checks belongs to dgetrf and not to dgecon. If that doesn't go through, it either means something went wrong or the matrix is singular so in any case NaN's are produced. This is rather not just fortunate but deliberate. And the if branch is well defined.

That's how most of LAPACK routines behave depending on their quick return behavior and I don't think you can initialize every case.

[pv]

thanks, lgtm, although indeed the code should be ok as it is even though a bit wonky