[6.2][Distributed] fix distributed thunk method descriptor mangling in IRGen #81831
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ktoso
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distributed
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@swift-ci please test |
ktoso
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ktoso
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May 29, 2025
| @@ -86,6 +86,8 @@ class IRGenMangler : public Mangle::ASTMangler { | |||
| beginMangling(); | |||
| appendEntity(func); | |||
| appendOperator("Tq"); | |||
| if (func->isDistributedThunk()) | |||
| appendSymbolKind(SymbolKind::DistributedThunk); | |||
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Description: While we mangle distributed thunks correctly in Mangler we did not update IRGenMangler to also handle them. This remained undiscovered until developers needed to use library evolution where these method descriptors are used, and the distributed_thunk descriptors would be mangled the same as the not-thunks, leading to duplicate symbols. This would result in .N suffixes and break the manled names in resilient witness tables.
Finally, this would manifest in runtime not being able to obtain a witness from the resilient witness table when library evolution is enabled, and causing null witnesses and crashes at runtime when attempting to make remote calls in such project.
This corrects the missing mangling part, which then corrects everything else implicitly -- since we no longer have duplicated symbols, and the thunks are uniqued correctly, everything falls into place and works well.
Scope/Impact: Distributed actors adopters which use library evolution. Specifically, attempts to make a remote call on a https://github.com/resolvable protocol would crash without this fix, making https://github.com/resolvable and the "server / client split" approach of distributed actors not usable at all with library evolution.
Risk: Low, the fix is very centralized to distributed thunks and sil witness tables of distributed protocol witnessing actors.
Testing: Added test verifying the emitted witness tables. Confirmed in real project hitting this problem that the solution is correct and resolves the crashes.
Reviewed by: @xedin
Original PR: #81805
Radar: rdar://144568615