Align unavailable Sendable diagnostics with the proposal for staging Sendable

lib/Sema/TypeCheckAvailability.cpp

@@ -1779,6 +1779,22 @@ void TypeChecker::diagnosePotentialAccessorUnavailability(
   fixAvailability(ReferenceRange, ReferenceDC, RequiredRange, Context);
 }
 
+static DiagnosticBehavior
+behaviorLimitForExplicitUnavailability(
+    const RootProtocolConformance *rootConf,
+    const DeclContext *fromDC) {
+  auto protoDecl = rootConf->getProtocol();
+
+  // Soften errors about unavailable `Sendable` conformances depending on the
+  // concurrency checking mode
+  if (protoDecl->isSpecificProtocol(KnownProtocolKind::Sendable) ||
+      protoDecl->isSpecificProtocol(KnownProtocolKind::UnsafeSendable)) {
+    return SendableCheckContext(fromDC).defaultDiagnosticBehavior();
+  }
+
+  return DiagnosticBehavior::Unspecified;
+}
+
 void TypeChecker::diagnosePotentialUnavailability(
     const RootProtocolConformance *rootConf,
     const ExtensionDecl *ext,
@@ -1795,11 +1811,13 @@ void TypeChecker::diagnosePotentialUnavailability(
     auto diagID = (ctx.LangOpts.EnableConformanceAvailabilityErrors
                    ? diag::conformance_availability_only_version_newer
                    : diag::conformance_availability_only_version_newer_warn);
+    auto behavior = behaviorLimitForExplicitUnavailability(rootConf, dc);
     auto err =
       ctx.Diags.diagnose(
                loc, diagID,
                type, proto, prettyPlatformString(targetPlatform(ctx.LangOpts)),
                reason.getRequiredOSVersionRange().getLowerEndpoint());
+    err.limitBehavior(behavior);
 
     // Direct a fixit to the error if an existing guard is nearly-correct
     if (fixAvailabilityByNarrowingNearbyVersionCheck(loc, dc,
@@ -2422,31 +2440,6 @@ bool swift::diagnoseExplicitUnavailability(const ValueDecl *D, SourceRange R,
   });
 }
 
-static DiagnosticBehavior
-behaviorLimitForExplicitUnavailability(const RootProtocolConformance *rootConf) {
-  auto protoDecl = rootConf->getProtocol();
-
-  // Soften errors about unavailable `Sendable` conformances depending on the
-  // concurrency checking mode
-  if (protoDecl->isSpecificProtocol(KnownProtocolKind::Sendable) ||
-      protoDecl->isSpecificProtocol(KnownProtocolKind::UnsafeSendable)) {
-    // TODO: Base this on concurrency checking mode from ExportContext so it
-    //       detects when you're in concurrency code without -warn-concurrency.
-    auto &langOpts = protoDecl->getASTContext().LangOpts;
-    if (langOpts.isSwiftVersionAtLeast(6))
-      /* fall through */;
-    else if (!langOpts.WarnConcurrency)
-      // TODO: Needs more conditions--should only do this if we aren't in a
-      //       concurrent context, and either the import or the declaration is
-      //       @predatesConcurrency.
-      return DiagnosticBehavior::Ignore;
-    else
-      return DiagnosticBehavior::Warning;
-  }
-
-  return DiagnosticBehavior::Unspecified;
-}
-
 /// Emit a diagnostic for references to declarations that have been
 /// marked as unavailable, either through "unavailable" or "obsoleted:".
 bool swift::diagnoseExplicitUnavailability(SourceLoc loc,
@@ -2482,11 +2475,12 @@ bool swift::diagnoseExplicitUnavailability(SourceLoc loc,
       // This was platform-specific; indicate the platform.
       platform = attr->prettyPlatformString();
       break;
-    } else {
-      // Downgrade unavailable Sendable conformances to warnings prior to
-      // Swift 6.
-      behavior = behaviorLimitForExplicitUnavailability(rootConf);
     }
+
+    // Downgrade unavailable Sendable conformance diagnostics where
+    // appropriate.
+    behavior = behaviorLimitForExplicitUnavailability(
+        rootConf, where.getDeclContext());
     LLVM_FALLTHROUGH;
 
   case PlatformAgnosticAvailabilityKind::SwiftVersionSpecific:

test/Concurrency/sendable_checking.swift

@@ -0,0 +1,42 @@
+// RUN: %target-typecheck-verify-swift
+// REQUIRES: concurrency
+// REQUIRES: OS=macosx
+
+@available(SwiftStdlib 5.1, *)
+struct NS1 { }
+
+@available(SwiftStdlib 5.1, *)
+@available(*, unavailable)
+extension NS1: Sendable { }
+// expected-note@-1 2{{conformance of 'NS1' to 'Sendable' has been explicitly marked unavailable here}}
+
+@available(SwiftStdlib 5.1, *)
+struct NS2 { // expected-note{{consider making struct 'NS2' conform to the 'Sendable' protocol}}
+  var ns1: NS1
+}
+
+@available(SwiftStdlib 5.1, *)
+struct NS3 { }
+
+@available(SwiftStdlib 5.3, *)
+extension NS3: Sendable { }
+
+@available(SwiftStdlib 5.1, *)
+func acceptCV<T: Sendable>(_: T) { }
+
+@available(SwiftStdlib 5.1, *)
+func testCV(ns1: NS1, ns1array: [NS1], ns2: NS2, ns3: NS3) {
+  acceptCV(ns1)
+  acceptCV(ns1array)
+  acceptCV(ns2)
+  acceptCV(ns3)
+}
+
+@available(SwiftStdlib 5.1, *)
+func testCV(ns1: NS1, ns1array: [NS1], ns2: NS2, ns3: NS3) async {
+  acceptCV(ns1) // expected-warning{{conformance of 'NS1' to 'Sendable' is unavailable}}
+  acceptCV(ns1array) // expected-warning{{conformance of 'NS1' to 'Sendable' is unavailable}}
+  acceptCV(ns2) // expected-warning{{type 'NS2' does not conform to the 'Sendable' protocol}}
+  acceptCV(ns3) // expected-warning{{conformance of 'NS3' to 'Sendable' is only available in macOS 11.0 or newer}}
+  // expected-note@-1{{add 'if #available' version check}}
+}