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[embedded] Fix associated type conformances for specialized witness tables #85644

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[embedded] Fix associated type conformances for specialized witness tables #85644

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f7aae22
[embedded] A few more test cases for existential casting
aschwaighofer Nov 20, 2025
0197784
[embedded] Tighten the check which existentials we support in embedde…
aschwaighofer Nov 20, 2025
8beaad6
[embedded] Allow casting to tuples
aschwaighofer Nov 20, 2025
920def9
[embedded] One more test
aschwaighofer Nov 20, 2025
60a28cd
embedded: don't re-abstract witness method calls for existentials
eeckstein Nov 11, 2025
b218d9a
SIL: add some APIs for `InitExistentialAddrInst`
eeckstein Nov 11, 2025
1486d00
AST: add `var ProtocolDecl.isMarkerProtocol`
eeckstein Nov 20, 2025
4191543
MandatoryPerformanceOptimizations: specialize witness tables for gene…
eeckstein Nov 11, 2025
ffca3b4
[embedded] Fix associate type conformances involving specialized conf…
aschwaighofer Nov 20, 2025
a5aa929
[embedded] Existentials: enable tests that now pass
aschwaighofer Nov 21, 2025
16206fa
[embedded] Enable all tests in general-existentials1.swift
aschwaighofer Nov 21, 2025
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4 changes: 4 additions & 0 deletions lib/IRGen/GenProto.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1751,6 +1751,10 @@ class AccessorConformanceInfo : public ConformanceInfo {
#endif

auto typeWitness = Conformance.getTypeWitness(assocType);
if (langOpts.hasFeature(Feature::EmbeddedExistentials) &&
SILWT->isSpecialized()) {
typeWitness = entry.getAssociatedTypeWitness().Witness;
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@slavapestov slavapestov Nov 21, 2025

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This doesn't make sense, why is Conformance.getTypeWitness() returning the wrong thing? Is Conformance is not a SpecializedProtocolConformance? If not, it should be fixed to match up and the conditional removed.

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@slavapestov slavapestov Nov 21, 2025

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You could use either Conformance.getTypeWitness() or entry.getAssociatedTypeWitness().Witness here, but they should be equal.

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@aschwaighofer aschwaighofer Nov 21, 2025

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Conformance.getTypeWitness returns the wrong thing because Conformance is the root conformance not the specialized_conformance.

Example:

protocol PWithAssoc {
  associatedtype Assoc
  func a() -> Assoc
}

struct Conformer<T> {
  var t: T
  init(_ t: T) {
    self.t = t
  }
}

struct Container<T> : PWithAssoc {
  var x: Conformer<T>

  init(_ t: T) {
    self.x = Conformer(t)
  }

  func a() -> Conformer<T> {
    return x
  }
}

func test(_ p: PWithAssoc) {
  let _ = p.a()
}

test(Container(1))

In this example, we have a specialized SILWitness table:

sil_witness_table shared [specialized] Container<Int>: specialize <Int> (<T> Container<T>: PWithAssoc module t3) {
  associated_type Assoc: Conformer<Int>
  method #PWithAssoc.a: <Self where Self : PWithAssoc> (Self) -> () -> Self.Assoc : @$e2t39ContainerVyxGAA10PWithAssocA2aEP1a0D0QzyFTWSi_Tg5    // specialized protocol witness for PWithAssoc.a() in conformance Container<A>
}

In the witnesstablebuilder code Conformance is initialized to the root conformance SILWT->getConformance()->getRootConformance():

  class WitnessTableBuilderBase {                                               
  protected:                                                                    
    IRGenModule &IGM;                                                           
    SILWitnessTable *SILWT;                                                     
    const RootProtocolConformance &Conformance;                                 
    const ProtocolConformance &ConformanceInContext;                            
    CanType ConcreteType;                                                       
                                                                                
    std::optional<FulfillmentMap> Fulfillments;                                 
                                                                                
    WitnessTableBuilderBase(IRGenModule &IGM, SILWitnessTable *SILWT)           
        : IGM(IGM), SILWT(SILWT),                                               
          Conformance(*SILWT->getConformance()->getRootConformance()),          
          ConformanceInContext(*mapConformanceIntoContext(SILWT->getConformance()->getRootConformance())),
          ConcreteType(Conformance.getDeclContext()                             
                         ->mapTypeIntoEnvironment(Conformance.getType())        
                         ->getCanonicalType()) {}

And that ends up being the normal conformance:

(normal_conformance type="Container<T>" protocol="PWithAssoc" explicit nonisolated
  (assoc_type req="Assoc" type="Conformer<T>")
  (value req="a()" witness="t3.(file).Container.a()@t3.swift:20:8")
  (assoc_conformance type="Self" proto="Copyable"
    (builtin_conformance type="Container<T>" protocol="Copyable" synthesized nonisolated))
  (assoc_conformance type="Self" proto="Escapable"
    (builtin_conformance type="Container<T>" protocol="Escapable" synthesized nonisolated))
  (assoc_conformance type="Self.Assoc" proto="Copyable"
    (builtin_conformance type="Conformer<T>" protocol="Copyable" synthesized nonisolated))
  (assoc_conformance type="Self.Assoc" proto="Escapable"
    (builtin_conformance type="Conformer<T>" protocol="Escapable" synthesized nonisolated)))

And then we end up with: (bound_generic_struct_type decl="t3.(file)[email protected]:6:8" (generic_type_param_type depth=0 index=0 name="T" param_kind=type)) Instead of Conformer<Int> for

auto typeWitness = Conformance.getTypeWitness(assocType);

If we used SILWT->getConformance().getTypeWitness(assocType) we would get the the right type (bound_generic_struct_type decl="t3.(file)[email protected]:6:8" (struct_type decl="Swift.(file).Int"))

}

if (IGM.Context.LangOpts.hasFeature(Feature::EmbeddedExistentials)) {
// In Embedded Swift associated type witness point to the metadata.
Expand Down
49 changes: 49 additions & 0 deletions test/embedded/existential.swift
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Expand Up @@ -302,6 +302,47 @@ func test13(_ p: any P4) {
p.t.printit()
}

struct GenericConformer<T> : ValuePrinter {
var t: T?
var l = (0, 1, 2, 3)

init(_ t: T) { self.t = t }

func printValue() {
print("GenericConformer \(l.0) \(l.1) \(l.2) \(l.3)")
}

mutating func mutate() {
l = (4, 5, 6, 7)
}
}

struct GenericConformerWithAssoc<T> : WithAssoc {
var g : GenericConformer<T>

init( _ g: T) {
self.g = GenericConformer(g)
}

func a() -> GenericConformer<T> {
return g
}
}

func test14(_ p: any ValuePrinter) {
print("test any ValuePrinter")
p.printValue()
var p2 = p
p2.mutate()
p2.printValue()
}

func test15(_ p: any WithAssoc) {
print("test any WithAssoc")
let l = p.a()
l.printValue()
}

@main
struct Main {
static func main() {
Expand Down Expand Up @@ -423,5 +464,13 @@ struct Main {
test13(P4Conformer())
// OUTPUT: test13
// OUTPUT: QConformer 3
// OUTPUT-NOT: deinit
test14(GenericConformer(1))
// OUTPUT: test any ValuePrinter
// OUTPUT: GenericConformer 0 1 2 3
// OUTPUT: GenericConformer 4 5 6 7
test15(GenericConformerWithAssoc(1))
// OUTPUT: test any WithAssoc
// OUTPUT: GenericConformer 0 1 2 3
}
}