switch to v0 mangling by default on stable #151994
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Following rust-lang#89117, rustc has defaulted to the v0 mangling scheme by default (since Nov 20th 2025). This surfaced two bugs: - rust-lang#138261 was a small ICE (found via fuzzing) where an implementation-internal namespace was missing for global assembly - this occurs with names instantiated within global assembly (that can happen inside constants) - rust-lang#134479 only occurs with unstable `generic_const_exprs` Since there have been three-to-four months for users to find bugs with this mangling scheme on nightly, that the scheme has been waiting many years to be stabilised, and has been used successfully internally at Microsoft, Meta and Google for many years, this patch proposes stabilising the v0 mangling scheme on stable. This patch does not propose removing the legacy mangling, it will remain usable on nightly as an escape-hatch if there are remaining bugs (though admittedly it would require switching to nightly for those on stable) - it is anticipated that this would be unlikely given current testing undergone by v0. Legacy mangling can be removed in another follow-up.
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This will require an FCP and probably another blog post as a follow-up to the previous one. |
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Following #89117, rustc has defaulted to the v0 mangling scheme by default (since Nov 20th 2025). This surfaced two bugs:
ICE: coverage:
symbol_names: unexpected DefPathData: GlobalAsm#138261 was a small ICE (found via fuzzing) where an implementation-internal namespace was missing for global assembly - this occurs with names instantiated within global assembly (that can happen inside constants)ICE: impossible case reached wit gce + v0 symbol mangling #134479 only occurs with unstable
generic_const_exprsSince there have been three-to-four months for users to find bugs with this mangling scheme on nightly, that the scheme has been waiting many years to be stabilised, and has been used successfully internally at Microsoft, Meta and Google for many years, this patch proposes stabilising the v0 mangling scheme on stable.
This patch does not propose removing the legacy mangling, it will remain usable on nightly as an escape-hatch if there are remaining bugs (though admittedly it would require switching to nightly for those on stable) - it is anticipated that this would be unlikely given current testing undergone by v0. Legacy mangling can be removed in another follow-up.
r? @wesleywiser