MAINT: Use intp output param viewable casts/methods (#20176)

This removes the cast-is-view flag with a more generic intp output.
Such an output could (theoretically) be nonzero, indicating e.g.
the offset of a complex number into a real one.
(We do not use this yet, though!)

The only "tricky" part is that the MinCastSafety helper used to
deal with the view-offset as well, and now we have to deal with it
explicitly when e.g. multiple fields have to be checked.

Bumps the experimental-dtype-api number, since the signatures changed.

* MAINT,DOC: Cleanups and clarfications based on Marten's comments

Co-Authored-By: Marten van Kerkwijk <mhvk@astro.utoronto.ca>

* MAINT: Rename `PyArray_GetCastSafety` to `PyArray_GetCastInfo`

Better captures the fact that it also returns the view-offset
information now.

* MAINT: Fix structured cast-is-view logic

* MAINT: Address review comments by Marten

Co-authored-by: Marten van Kerkwijk <mhvk@astro.utoronto.ca>

1 files changed, 6 insertions, 5 deletions

diff --git a/numpy/testing/print_coercion_tables.py b/numpy/testing/print_coercion_tables.py
index 3a447cd2d..c1d4cdff8 100755
--- a/numpy/testing/print_coercion_tables.py
+++ b/numpy/testing/print_coercion_tables.py
@@ -87,11 +87,12 @@ def print_new_cast_table(*, can_cast=True, legacy=False, flags=False):
     from numpy.core._multiarray_tests import get_all_cast_information
 
     cast_table = {
-        0 : "#",  # No cast (classify as equivalent here)
-        1 : "#",  # equivalent casting
-        2 : "=",  # safe casting
-        3 : "~",  # same-kind casting
-        4 : ".",  # unsafe casting
+        -1: " ",
+        0: "#",  # No cast (classify as equivalent here)
+        1: "#",  # equivalent casting
+        2: "=",  # safe casting
+        3: "~",  # same-kind casting
+        4: ".",  # unsafe casting
     }
     flags_table = {
         0 : "▗", 7: "█",