Concurrency: Move PackExpansionType check to swift::diagnoseNonSendableTypes()

This was added in #80220 to fix a related issue with captures of packs,
but it's even better to sink this down into diagnoseNonSendableTypes(),
so that we can handle packs in parameter position as well.

- Fixes #82614.
- Fixes rdar://problem/154649522.

Author: slavapestov

lib/Sema/TypeCheckConcurrency.cpp

@@ -1052,11 +1052,17 @@ bool swift::diagnoseNonSendableTypes(
     Type type, SendableCheckContext fromContext,
     Type inDerivedConformance, SourceLoc loc,
     llvm::function_ref<bool(Type, DiagnosticBehavior)> diagnose) {
+  auto &ctx = type->getASTContext();
+
   // If the Sendable protocol is missing, do nothing.
-  auto proto = type->getASTContext().getProtocol(KnownProtocolKind::Sendable);
+  auto proto = ctx.getProtocol(KnownProtocolKind::Sendable);
   if (!proto)
     return false;
 
+  // Unwrap pack expansions here to allow packs of Sendable type.
+  if (auto *expansion = type->getAs<PackExpansionType>())
+    type = PackType::get(ctx, {expansion});
+
   // FIXME: More detail for unavailable conformances.
   auto conformance = lookupConformance(type, proto, /*allowMissing=*/true);
   if (conformance.isInvalid() || conformance.hasUnavailableConformance()) {
@@ -3055,12 +3061,6 @@ namespace {
             ->mapTypeIntoContext(decl->getInterfaceType())
             ->getReferenceStorageReferent();
 
-        // Pack expansions are okay to capture as long as the pattern
-        // type is Sendable.
-        if (auto *expansion = type->getAs<PackExpansionType>()) {
-          type = expansion->getPatternType();
-        }
-
         if (type->hasError())
           continue;
 

test/Concurrency/sendable_checking.swift

@@ -534,3 +534,27 @@ func test(value: (_: Int, _: () -> Void)) {
   takesSendable(value.1) // Ok
   // expected-warning@-1 {{converting non-Sendable function value to '@Sendable () -> Void' may introduce data races}}
 }
+
+// Don't forget about parameter packs -- https://github.com/swiftlang/swift/issues/82614
+
+@available(SwiftStdlib 5.1, *)
+protocol PackProto {
+  func foo<each A: Sendable>(_ a: repeat each A) async
+  func bar<each A>(_ a: repeat each A) async
+  // expected-note@-1 {{consider making generic parameter 'each A' conform to the 'Sendable' protocol}}
+}
+
+@available(SwiftStdlib 5.1, *)
+actor PackActor: PackProto {
+  func foo<each A: Sendable>(_ a: repeat each A) async {
+    for b in repeat (each a) {
+      print(b)
+    }
+  }
+  func bar<each A>(_ a: repeat each A) async {
+  // expected-warning@-1 {{non-Sendable parameter type 'repeat each A' cannot be sent from caller of protocol requirement 'bar' into actor-isolated implementation; this is an error in the Swift 6 language mode}}
+    for b in repeat (each a) {
+      print(b)
+    }
+  }
+}