inconsistent default size type between CrsMatrix and StaticCrsGraph

[maartenarnst]

@brian-kelley
@romintomasetti

In the following PR:

• Use default_size_type as default offset in matrix types #2149

the default size types of KokkosSparse::CrsMatrix and several other matrix types were changed to default_size_type. This is typically int or size_t depending on the configuration of Kokkos-kernels.

However, in Kokkos::StaticCrsGraph, the default size type is taken from a ViewTraits instance. Typically, that size type is in turn a size type of a space, and it need not be int or size_t.

• https://github.com/kokkos/kokkos/blob/a14a5d9bee2f84e1b160df203ed2dd6c8f2060c3/containers/src/Kokkos_StaticCrsGraph.hpp#L256-L260

The issue is thus that these default size types are not necessarily the same. And because KokkosSparse::CrsMatrix and Kokkos::StaticCrsGraph are so interrelated, this discrepancy can lead to problems when using eg. the KokkosSparse::CrsMatrix constructor that takes a Kokkos::StaticCrsGraph among its arguments.

This issue is thus a suggestion to consider whether further consistency across the size types may be worth pursuing.

[maartenarnst]

@lucbv

Looks like it will be solved :)

[lucbv]

Yes, it was good timing you reminded me about this, I was able to "jump on it" effectively during the meeting.
Since we are the biggest user of this container I think it is reasonable to move it : )