cs2gs: preserve designations on nested untyped property patterns (selfmig nightly regression) - #3631
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The untyped recursive-pattern branch of TranslateRecursivePattern never
consulted `recursive.Designation`, so a designation on a nested property
pattern — `case { ClrType: { IsGenericType: true } closedClr }:` — was
silently dropped while the body still referenced the binder, producing
G# that fails GS0125/GS0159. This is the 2026-08-29 selfmig nightly
regression: TupleElementNamesReader.cs (#3622) uses exactly this shape,
so migrated src/Core stopped compiling and 18 downstream apps went red
(28/52 green vs floor 33).
G# already supports the after-brace designator natively (ADR-0166
`PropertyPattern identifier?`), and the code model + printer already
carry it — the translator now populates it, with the reassigned-binder
capture mirroring the var-pattern path. Covers switch statements, switch
expressions, and boolean is-patterns; verified end to end (compile+run
parity with the C#).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Nng28yiBdPVdeML7mSZphs
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Aug 29, 2026
…jection gate (ADR-0172) (#3632) Fixes the remaining systemic failure in the second 2026-08-29 selfmig nightly ([run 33260247720](https://github.com/DavidObando/gsharp/actions/runs/33260247720), which already included #3630/#3631): 32/52 green against floor 33, with migrated **Cs2Gs.Translator** failing `GS0158 Cannot find member Symbol` / `GS0159 Cannot find function Contains` / `GS0116 not indexable` at `CSharpToGSharpTranslator.Constructors.gs:1537-38` — `candidate[0].Symbol` and `reach[head].Contains(symbol)` over `List[List[(syntax …, symbol …)]]` — cascading into 11 downstream apps. ## Root cause A named tuple nested **inside** a generic type argument shares its CLR backing with the unnamed shape (`ValueTuple<…>`), so any keep-symbolic gate that consults only `RequiresSymbolicProjection` (or a direct `is TupleTypeSymbol`) collapses the constructed type to its erased CLR form — and the element names vanish, so member access by name fails. The #3622 projection-gate family covered *direct* named-tuple arguments (`List[(a, b)]`, one level), but not `List[List[(a, b)]]`, `List[[](a, b)]`, or `Dictionary[K, (a, b)]` reached through construction, indexing, or iteration. Minimal repro (failed before, runs now): ```gs let groups = List[List[(a int32, b string)]]() … groups[0][0].a // was GS0158: Cannot find member a ``` ## Fix Widened six keep-symbolic gates with `TypeSymbol.ContainsNamedTupleElements` (already recursive through every constructor shape): the generic ctor-call type-argument resolution (the erasure at the root), the constructed-generic receiver form, the indexer element substitution + its #2365 recursive projection filter, the generic-return construction and indexer property projection in MemberLookup, the conversion-classifier parameter substitution, and the type-clause `ProjectGenericArgument`. Deliberately did **not** widen `ImportedTypeSymbol.HasSubstitutableTypeArgument` itself — it feeds conversion/lowering decisions with broader meaning, and widening it regressed working cases during investigation. ## Verification - New `NestedNamedTupleProjectionTests` (4 end-to-end oracle tests) pin all shapes, including the exact selfmig iteration+index+member chain with an imported interface element type. - Full Core.Tests: **8218/8218 passed**. - Local selfmig proof over the cs2gs subtree: Cs2Gs.Translator's three real compile errors are gone (the only remaining local failures are the known subtree-proof artifact — `GSharpRoundTrip.gs` referencing GSharp.Core, which the subtree run excludes from migration; the nightly migrates it). With this plus #3630/#3631, the next nightly should clear the `b7a89d8f22f8`/`0a665d0d062c`/`ebe7e1f2f6f8` fingerprint family. The `!!` ceiling breach (17516 vs 17400) is a separate ratchet question. 🤖 Generated with [Claude Code](https://claude.com/claude-code) https://claude.ai/code/session_01Nng28yiBdPVdeML7mSZphs Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
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Fixes the systemic failure in the 2026-08-29 selfmig nightly (run 33234797980): 18 apps shared the same two compile fingerprints (
GS0159 Cannot find function GetGenericArguments/GS0125 Variable 'closedClr' doesn't exist), all cascading from migratedsrc/Corefailing to compile — which dropped the gate to 28/52 green against floor 33.Root cause
TranslateRecursivePattern's untyped branch returnednew PropertyPattern(fields)without ever consultingrecursive.Designation. A designation on a nested untyped property pattern was silently dropped while the body still referenced the binder:translated to a pattern without
closedClr, orphaning the body references.Fix
G# natively supports the after-brace designator (ADR-0166,
PropertyPattern identifier?in the spec grammar), and the code model + printer already carry aDesignator— the translator now populates it, with reassigned-binder capture mirroring the existing var-pattern path, and an explicit unsupported report for tuple designations. Verified that gsc compiles and runs the nested-designation form correctly (narrowed non-nil binding, parity with C# semantics).Tests
NestedPatternDesignationTranslationTests— switch statement (with compile+run parity witness: generic vs nil holder), booleanis-pattern, and switch expression. Full pattern-related Cs2Gs.Tests family green (188/188).Note: this is independent of #3630; the C# trigger shape came from #3622 (merged), so the regression exists on main regardless of the variadic-carriers branch.
🤖 Generated with Claude Code
https://claude.ai/code/session_01Nng28yiBdPVdeML7mSZphs