This was previously broken by the introduction of the "__PYX_ERR()" macro.

Fix a typo that prevented UtilityCode.get_tree(entries_only=True) from working as expected. It looks like this doesn't make a difference for the generated C code (at least for the pickling, C++ STL and memoryview tests), but it should reduce the time it takes to collect the symtab entries defined in the tree.

Instead of simply asserting that the error exit case and the success exit case of a nogil function are aligned, make sure they are before joining them back together.
This is necessary because the error code path is more likely to require the GIL for cleanup operations than the success path – which is a good thing, actually, so we try to streamline the success case at the expense of more work on the error path.

Move assertion where it actually belongs, since it does not apply to the buffer cleanup case (which semantically jumps over it with a 'goto').

Move the branch-hint generation from Nodes.py into Optimize.py to make it available to tree assertion tests (and add such a test).

Support the 'assert' statement in nogil sections, as long as it has a plain C condition and constant message (string) value.

Closes #3558.

Would be nice to allow this also for the print() function, but that's tricky because we have to insert the "GILStatNode" before analysing the declarations, which is when we learn if it's really the builtin print function or something else.

Acquire the GIL in nogil functions only when strictly needed on function exit, e.g. for cleaning up temp variables from with-gil blocks or adding tracebacks.

Closes GH-3554.

Allow C functions/variables with names starting with "__" to be found
from within classes, even though their names would normally be
inaccessible due to the Python "class private names" mechanism.
https://github.com/cython/cython/issues/3544

Warn about unmangled Python names that are being found and used, since they do not adhere to Python lookup rules.

Removed `mangle_special_name` in favour of `mangle_class_private_name`,
which previously applied slightly different rules for creating vs looking up variables.

Closes #3548.

This reverts commit f09e61ab.

Fix reference to missing utility function, which is not more than an alias to CPython's "PyObject_GenericGetAttr" in the limited API case.

Clean up and repair the type spec generation for the limited API, leaving more of the work to the TypeSlots instead of special-casing all sorts of things.

Ideally, most of the code that is uninteresting for users should be out of the way and not reside before the translated user code.
Mark all code section name beginnings in the C code file to make them easier to follow and move around.

Fix C-code indentation of PyModuleDef struct by avoiding duplicate opening braces in conditional code.

* Changed always_allow_keywords_T295 for Py3.9

https://bugs.python.org/issue37645 appears to change some error
messages slightly (including the qualname and not just the
function name). This change just allows doctest to cope with
both the new and old messages