gh-87613: Use AC vectorcall for weakref.ref()

[eendebakpt]

Convert weakref.ref.__new__ to Argument Clinic with the @vectorcall decorator. weakref.ref.__init__, which only validates the arguments that __new__ already consumed, is converted to Argument Clinic as well. This will also improve the signature of weakref.ref.

+------------------------------+---------------+-----------------------+
| Benchmark                    | weakref_base3 | weakref_patch3        |
+==============================+===============+=======================+
| ref(o)                       | 116 ns        | 89.1 ns: 1.31x faster |
+------------------------------+---------------+-----------------------+
| ref(O())                     | 183 ns        | 172 ns: 1.07x faster  |
+------------------------------+---------------+-----------------------+
| ref(o, cb)                   | 121 ns        | 77.9 ns: 1.55x faster |
+------------------------------+---------------+-----------------------+
| o in WeakSet                 | 287 ns        | 216 ns: 1.32x faster  |
+------------------------------+---------------+-----------------------+
| WeakSet.add; WeakSet.discard | 424 ns        | 324 ns: 1.31x faster  |
+------------------------------+---------------+-----------------------+
| Geometric mean               | (ref)         | 1.30x faster          |
+------------------------------+---------------+-----------------------+

Benchmark script

import pyperf
runner = pyperf.Runner()
setup = """
from weakref import ref, WeakSet
class O: pass
o = O()
cb = lambda r: None
ws = WeakSet()
ws.add(o)
"""
runner.timeit("ref(o)", "ref(o)", setup)
runner.timeit("ref(O())", "ref(O())", setup)
runner.timeit("ref(o, cb)", "ref(o, cb)", setup)
runner.timeit("o in WeakSet", "o in ws", setup)
runner.timeit("WeakSet.add; WeakSet.discard", "ws.add(o); ws.discard(o)", setup)

Generated with help from Claude Code

• Issue: Generate vectorcall code to parse arguments using Argument Clinic #87613

[cmaloney]

This looks good to me. Not a ton of usage but some in the import machinery which will help startup a bit. Have been looking at similar for some common decorators.

[cmaloney]

nit: Should this be called "object" to match the docs https://docs.python.org/3/library/weakref.html#weakref.ref

[eendebakpt]

Hmm. This is positional only, so not too important but I think that would indeed be better.

Note: the subclass KeyedRef is not positional only, and uses the name ob.