Merge pull request #67566 from slavapestov/referenced-generic-params

Sema: Fix two problems in checkReferencedGenericParams() analysis

Author: slavapestov

lib/Sema/TypeCheckGeneric.cpp

@@ -341,6 +341,25 @@ void TypeChecker::checkReferencedGenericParams(GenericContext *dc) {
         ReferencedGenericParams.insert(ty->getCanonicalType());
         return Action::SkipChildren;
       }
+
+      // Skip the count type, which is always a generic parameter;
+      // we don't consider it a reference because it only binds the
+      // shape and not the metadata.
+      if (auto *expansionTy = ty->getAs<PackExpansionType>()) {
+        expansionTy->getPatternType().walk(*this);
+        return Action::SkipChildren;
+      }
+
+      // Don't walk into generic type alias substitutions. This does
+      // not constrain `T`:
+      //
+      //   typealias Foo<T> = Int
+      //   func foo<T>(_: Foo<T>) {}
+      if (auto *aliasTy = dyn_cast<TypeAliasType>(ty.getPointer())) {
+        Type(aliasTy->getSinglyDesugaredType()).walk(*this);
+        return Action::SkipChildren;
+      }
+
       return Action::Continue;
     }
 

test/type/pack_expansion.swift

@@ -65,6 +65,7 @@ struct Outer<each T> {
 func packRef<each T>(_: repeat each T) where repeat each T: P {}
 
 func packMemberRef<each T>(_: repeat (each T).T) where repeat each T: P {}
+// expected-error@-1 {{generic parameter 'T' is not used in function signature}}
 
 // expected-error@+1 {{'each' cannot be applied to non-pack type 'Int'}}{{31-35=}}
 func invalidPackRefEachInt(_: each Int) {}
@@ -98,3 +99,11 @@ func golden<Z>(_ z: Z) {}
 func hour<each T>(_ t: repeat each T)  {
   _ = (repeat golden(each t))
 }
+
+func unusedParameterPack1<each T: Sequence>(_: repeat (each T).Element) {}
+// expected-error@-1 {{generic parameter 'T' is not used in function signature}}
+
+typealias First<T, U> = T
+
+func unusedParameterPack2<each T>(_: repeat First<Int, each T>) {}
+// expected-error@-1 {{generic parameter 'T' is not used in function signature}}