fix ref bug with iter, views and istr

[Vizonex]

What do these changes do?

This is based off previous things that I have referenced in #1310 and #1306. The other bugs listed seem to like much harder puzzles to solve than anything else so I'm tackling the easy fixable ones first.

Reproducer

"""Reproducer: multidict iterator/view/istr types leak type references.

iter.h:134 — multidict_iter_dealloc: no Py_DECREF(Py_TYPE(self))
views.h:30 — multidict_view_dealloc: no Py_DECREF(Py_TYPE(self))
istr.h:22 — istr_dealloc: no Py_DECREF(Py_TYPE(self))
traverse functions also missing Py_VISIT(Py_TYPE(self)).

Tested: multidict 6.7.1, Python 3.14.
"""
from multidict import MultiDict, istr
import sys

md = MultiDict([("a", "1"), ("b", "2")])

# Test iterator type leak
it = iter(md.keys())
iter_type = type(it)
del it
baseline = sys.getrefcount(iter_type)
for i in range(1000):
    it = iter(md.keys())
    list(it)
    del it
after = sys.getrefcount(iter_type)
print(f"KeysIter type: baseline={baseline}, after={after}, leaked={after-baseline}")

# Test view type leak
view_type = type(md.keys())
baseline = sys.getrefcount(view_type)
for i in range(1000):
    v = md.keys()
    del v
after = sys.getrefcount(view_type)
print(f"KeysView type: baseline={baseline}, after={after}, leaked={after-baseline}")

# Test istr type leak
baseline = sys.getrefcount(istr)
for i in range(1000):
    s = istr("hello")
    del s
after = sys.getrefcount(istr)
print(f"istr type:     baseline={baseline}, after={after}, leaked={after-baseline}")

# Expected: 0 leaked for all
# Actual: exactly 1000 leaked for each — one per object lifecycle

Are there changes in behavior for the user?

Related issue number

Checklist

• I think the code is well written
• Unit tests for the changes exist
• Documentation reflects the changes

[bdraco]

Would you please add a test for this one as well ?

[Vizonex]

Would you please add a test for this one as well ?

Just did. :)

[Vizonex]

Seems this implementation likes to segfault :( I'll probably go back and replan a few things tomorrow when I have 2 days off from my job.

[Vizonex]

@bdraco I seem to have just fixed the problem. Turns out using a Py_tp_free can be very useful. I think what occurred was that the rewrite was modeled after the python standard library a little bit too deeply. I decided it might be smart to try another implementation such as freeing the type afterwards.

[codspeed-hq]

Merging this PR will not alter performance

✅ 245 untouched benchmarks

---

_{Comparing Vizonex:iterator-ref-leak (c06e3a0) with master (f74b0b8)}

[Vizonex]

The only bad news is that freethreaded is still bugged.

[Vizonex]

@bdraco It should also be mentioned that code-coverage is somehow failing in the isolated directory. I've looked at them and most files seem to act that way at around 33.33% or similar results. I wonder if this coverage is inaccurate or should be fixed?

[codecov]

Codecov Report

❌ Patch coverage is 11.11111% with 24 lines in your changes missing coverage. Please review.
✅ Project coverage is 96.94%. Comparing base (f74b0b8) to head (c06e3a0).

Files with missing lines	Patch %	Lines
tests/isolated/multidict_type_leak.py	11.11%	23 Missing and 1 partial ⚠️

❌ Your patch check has failed because the patch coverage (11.11%) is below the target coverage (95.00%). You can increase the patch coverage or adjust the target coverage.
❌ Your project check has failed because the head coverage (96.08%) is below the target coverage (100.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1311      +/-   ##
==========================================
- Coverage   97.60%   96.94%   -0.66%     
==========================================
  Files          26       27       +1     
  Lines        3513     3540      +27     
  Branches      253      257       +4     
==========================================
+ Hits         3429     3432       +3     
- Misses         77      100      +23     
- Partials        7        8       +1     

Flag	Coverage Δ
CI-GHA	96.94% <11.11%> (-0.66%)	⬇️
pytest	96.94% <11.11%> (-0.66%)	⬇️

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