AST: Handle missing cases in findGenericParameterReferencesRec()

Author: slavapestov

lib/AST/Decl.cpp

@@ -4954,7 +4954,7 @@ findGenericParameterReferencesRec(CanGenericSignature genericSig,
     // Don't forget to look in the parent.
     if (const auto parent = nominal->getParent()) {
       info |= findGenericParameterReferencesRec(
-          genericSig, genericParam, parent, position,
+          genericSig, genericParam, parent, TypePosition::Invariant,
           /*canBeCovariantResult=*/false);
     }
 
@@ -5033,10 +5033,40 @@ findGenericParameterReferencesRec(CanGenericSignature genericSig,
     return info;
   }
 
-  if (!type->isTypeParameter()) {
+  // Packs are invariant.
+  if (auto *pack = type->getAs<PackType>()) {
+    auto info = GenericParameterReferenceInfo();
+
+    for (auto arg : pack->getElementTypes()) {
+      info |= findGenericParameterReferencesRec(
+          genericSig, genericParam, arg,
+          TypePosition::Invariant, /*canBeCovariantResult=*/false);
+    }
+
+    return info;
+  }
+
+  // Pack expansions are invariant.
+  if (auto *expansion = type->getAs<PackExpansionType>()) {
+    return findGenericParameterReferencesRec(
+        genericSig, genericParam, expansion->getPatternType(),
+        TypePosition::Invariant, /*canBeCovariantResult=*/false);
+  }
+
+  // Specifically ignore parameterized protocols and existential
+  // metatypes because we can erase them to the upper bound.
+  if (type->is<ParameterizedProtocolType>() ||
+      type->is<ExistentialMetatypeType>()) {
     return GenericParameterReferenceInfo();
   }
 
+  // Everything else should be a type parameter.
+  if (!type->isTypeParameter()) {
+    llvm::errs() << "Unhandled type:\n";
+    type->dump(llvm::errs());
+    abort();
+  }
+
   Type selfTy(genericParam);
   if (!type->getRootGenericParam()->isEqual(selfTy)) {
     return GenericParameterReferenceInfo();

test/decl/protocol/existential_member_accesses_self_assoctype.swift

@@ -1025,6 +1025,10 @@ do {
   let _: Dictionary<String, any Class2Base & CovariantAssocTypeErasureDerived> = exist.method12()
 }
 
+///
+/// Interactions between opening and parameter packs
+///
+
 // Same-shape requirements
 protocol HasSameShape {
   func foo<each T, each U>(t: repeat each T, u: repeat each U) -> (repeat (each T, each U))
@@ -1033,3 +1037,29 @@ protocol HasSameShape {
 func bar(a: any HasSameShape) -> (Int, String) {
   a.foo(t: 1, u: "hi")
 }
+
+// Make sure we look through a pack type when evaluating the variance of the result
+struct Variadic<each A> {}
+
+protocol VariadicResult {
+  associatedtype A
+  func foo() -> Variadic<A>
+}
+
+func variadicResult(a: any VariadicResult) {
+  a.foo()
+  // expected-error@-1 {{member 'foo' cannot be used on value of type 'any VariadicResult'; consider using a generic constraint instead}}
+}
+
+// Pack expansions are invariant
+struct Pair<X, Y> {}
+
+protocol PackExpansionResult {
+  associatedtype A
+  func foo<each T>(t: repeat each T) -> (repeat Pair<each T, A>)
+}
+
+func packExpansionResult(p: any PackExpansionResult) {
+  p.foo(t: 1, "hi")
+  // expected-error@-1 {{member 'foo' cannot be used on value of type 'any PackExpansionResult'; consider using a generic constraint instead}}
+}