[Sergio Pedri (Sergio0694)]

Summary

Share the active member scan's reservation across a whole module (instead of a lexical family) in the interop generator's generic discovery, so that large test projects no longer hit CSWINRTINTEROPGEN0106 while the existing recursion guards remain in place.

Motivation

Replaying the Store test-project debug repros (Desktop, BusinessLogic, Purchase) produced CSWINRTINTEROPGEN0106 warnings (Desktop: 2, BusinessLogic: 2, Purchase: 0). Debug logs showed the 1024 reservation budget being consumed by generic helper expansion spread across many unrelated types in the same module (mocking libraries such as Moq). The existing lexical-family rule from #2619 only applied to a type and its nested definitions, so it did not cover these transitions even though they stay within a single, finite module at an unchanged closed substitution.

With this change, ordinary member transitions at an unchanged, fully closed substitution within the same resolved module share the active scan's reservation. This is an accounting rule only: members are still scanned and considered for marshalling. Changing arguments or crossing into another module still costs a reservation, and the visited-key deduplication, FIFO ordering, depth limit (32), signature complexity limit (256) and the 1024 reservation budget are all unchanged, so genuine recursion is still bounded. The 1024 limit is not increased.

Shared transitions are not charged, so they get their own allowance of 4096 per enumeration. Once it is exhausted, further candidates are charged against the normal 1024 budget, so a pathologically wide module still reaches CSWINRTINTEROPGEN0106. The highest shared count measured on the Store repros was about 1600.

Validation on the three repros: all 0106 warnings disappear and the generated WinRT.Interop.dll is byte-identical to the baseline (re-verified with the cap). End-to-end benchmarking over 264 accepted runs (baseline, this change, an increased-limit variant, and a baseline-copy control) showed no measurable performance impact beyond run-to-run noise, with memory within ±2% in 17 of 18 cells.

Changes

• src/WinRT.Interop.Generator/Discovery/TypeSignatureDiscovery.MemberScanContext.cs: remove GetLexicalFamily and the family identity; MemberScanContext now carries the declaring ModuleDefinition and compares module identity when deciding whether a transition can share the reservation. Sharing consumes a separate allowance (MaxSharedReservations, 4096) and falls back to normal charging once it is exhausted.
• src/WinRT.Interop.Generator/Discovery/TypeSignatureDiscovery.Members.cs and src/WinRT.Interop.Generator/Discovery/TypeSignatureDiscovery.Worklist.cs: create the member scan context from, and pass to CanShareMemberReservation, the declaring module instead of the declaring type, and update the related comments.
• src/WinRT.Interop.Generator/Discovery/TypeSignatureDiscovery.cs: add MaxSharedReservations and its counter, and update the MaxTransitiveTypes doc comment.
• src/Tests/ProjectionWriterTest/Test_InteropGenericDiscovery.MemberReservations.cs (renamed from ...LexicalFamilies.cs): tests now cover sharing across unrelated types within a module, rejection across modules, changed-argument limits, open-context behavior and the shared allowance bound.
• src/Tests/ProjectionWriterTest/Test_InteropGenericDiscovery.StaticDispatchLimits.cs: update the expected Node count (1022 to 1023), since Required<string> now shares the instance default's reservation.
• .github/skills/interop-generator/SKILL.md: document the module-scoped sharing policy and the shared allowance.

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