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gh-132983: _zstd: use Py_UNREACHABLE in _zstd_load_impl - #137320

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Rogdham:zstd_load_impl_pyunreachable
Aug 4, 2025
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gh-132983: _zstd: use Py_UNREACHABLE in _zstd_load_impl#137320
AA-Turner merged 1 commit into
python:mainfrom
Rogdham:zstd_load_impl_pyunreachable

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@Rogdham

@RogdhamRogdham commented Aug 2, 2025•
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There are 2 functions called _zstd_load_impl: one for compression and one for decompression.

In these functions, the type variable is supposed to represent the dict type. Due to the way the function is called, the dict type is always one of DICT_TYPE_DIGESTED/DICT_TYPE_UNDIGESTED/DICT_TYPE_PREFIX. However, the implementations differs in the unreachable case:

This PR harmonizes the two implementations by using Py_UNREACHABLE.

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@picnixzpicnixz added needs backport to 3.14 bugs and security fixes skip news labels Aug 2, 2025
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picnixz requested a review from emmatypingAugust 2, 2025 09:13
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emmatyping approved these changes Aug 2, 2025
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Thank you!

ZeroIntensity
ZeroIntensity approved these changes Aug 3, 2025
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LGTM as well.

@emmatyping Would you like to use your new green button?

AA-Turner
AA-Turner reviewed Aug 3, 2025
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Does it make sense to have a test that we don't hit this unreachable path?

@ZeroIntensity

ZeroIntensity commented Aug 4, 2025

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Hm, how are you envisioning that? The whole point of Py_UNREACHABLE here is that no code path can hit it, so there's not really a test we could write to stress that.

@AA-Turner

AA-Turner commented Aug 4, 2025

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I'm not a fan of needing logic like this, and it would be nice to exhaustively test that we never hit it, but I haven't had a good idea, no.

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@AA-Turner

AA-Turner commented Aug 4, 2025

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Anyway, the compression path already uses Py_UNREACHABLE, so likely best to merge for pragmatism.

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@AA-Turner
AA-Turner merged commit 57eab1b into python:mainAug 4, 2025
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miss-islington-appBot commented Aug 4, 2025

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Thanks @Rogdham for the PR, and @AA-Turner for merging it 🌮🎉.. I'm working now to backport this PR to: 3.14.
🐍🍒⛏🤖 I'm not a witch! I'm not a witch!

miss-islington pushed a commit to miss-islington/cpython that referenced this pull request Aug 4, 2025
@Rogdham@miss-islington
pythongh-132983: UsePy_UNREACHABLEin_zstd_load_impl()(pyt…
62f57a6
…honGH-137320)
(cherry picked from commit 57eab1b)
Co-authored-by: Rogdham <3994389+Rogdham@users.noreply.github.com>
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GH-137360 is a backport of this pull request to the 3.14 branch.

@bedevere-appbedevere-appBot removed the needs backport to 3.14 bugs and security fixes label Aug 4, 2025
@Rogdham
Rogdham deleted the zstd_load_impl_pyunreachable branch August 4, 2025 06:27
hugovk pushed a commit that referenced this pull request Aug 7, 2025
@miss-islington@Rogdham
[3.14]gh-132983: UsePy_UNREACHABLEin_zstd_load_impl()(GH…
0fc49be
…-137320) (#137360)
Co-authored-by: Rogdham <3994389+Rogdham@users.noreply.github.com>
Agent-Hellboy pushed a commit to Agent-Hellboy/cpython that referenced this pull request Aug 19, 2025
@Rogdham@Agent-Hellboy
pythongh-132983: UsePy_UNREACHABLEin_zstd_load_impl()(pyt…
4f35853
…hon#137320)
kumaraditya303 pushed a commit to miss-islington/cpython that referenced this pull request Sep 9, 2025
@miss-islington@Rogdham@kumaraditya303
[3.14]pythongh-132983: UsePy_UNREACHABLEin ``_zstd_load_impl()…
301dcde
…`` (pythonGH-137320) (python#137360)
Co-authored-by: Rogdham <3994389+Rogdham@users.noreply.github.com>
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