[Concurrency] TildeSendable: Lift the check up to cover isolated types

If a type is suppressing `~Sendable` global-actor isolation shouldn't
make it `Sendable` and the compiler should diagnose cases were `Sendable`
comes from an isolated protocol.

Author: xedin

lib/Sema/TypeCheckConcurrency.cpp

@@ -7375,6 +7375,24 @@ bool swift::checkSendableConformance(
       return false;
   }
 
+  // Sendable supression allows conditional conformances only.
+  if (nominal->suppressesConformance(KnownProtocolKind::Sendable)) {
+    bool hasUnconditionalConformance = false;
+    if (auto *normalConf = dyn_cast<NormalProtocolConformance>(conformance)) {
+      hasUnconditionalConformance =
+          normalConf->getConditionalRequirements().empty();
+    }
+
+    if (hasUnconditionalConformance) {
+      if (!isImplicitSendableCheck(check)) {
+        auto *conformanceDecl =
+            conformanceDC->getAsDecl() ? conformanceDC->getAsDecl() : nominal;
+        conformanceDecl->diagnose(diag::non_sendable_type_suppressed);
+      }
+      return true;
+    }
+  }
+
   // Global-actor-isolated types can be Sendable. We do not check the
   // instance data because it's all isolated to the global actor.
   switch (getActorIsolation(nominal)) {
@@ -7458,24 +7476,6 @@ bool swift::checkSendableConformance(
   if (wasImplied)
     conformanceDC = nominal;
 
-  // Sendable supression allows conditional conformances only.
-  if (nominal->suppressesConformance(KnownProtocolKind::Sendable)) {
-    bool hasUnconditionalConformance = false;
-    if (auto *normalConf = dyn_cast<NormalProtocolConformance>(conformance)) {
-      hasUnconditionalConformance =
-          normalConf->getConditionalRequirements().empty();
-    }
-
-    if (hasUnconditionalConformance) {
-      if (!isImplicitSendableCheck(check)) {
-        auto *conformanceDecl =
-            conformanceDC->getAsDecl() ? conformanceDC->getAsDecl() : nominal;
-        conformanceDecl->diagnose(diag::non_sendable_type_suppressed);
-      }
-      return true;
-    }
-  }
-
   return checkSendableInstanceStorage(nominal, conformanceDC, check);
 }
 

test/Sema/tilde_sendable.swift

@@ -27,6 +27,9 @@ extension InExt: ~Sendable { // expected-error {{conformance to inferrable proto
 func test<T: ~Sendable>(_: T) {} // expected-error {{conformance to 'Sendable' can only be suppressed on structs, classes, and enums}}
 func test<Q>(other: Q) where Q: ~Sendable {} // expected-error {{type 'Sendable' cannot be suppressed}}
 
+func testSendable<T: Sendable>(_: T) {}
+
+
 struct Generic<T: ~Sendable> { // expected-error {{conformance to 'Sendable' can only be suppressed on structs, classes, and enums}}
   var x: T
 }
@@ -47,10 +50,8 @@ do {
     // expected-error@-1 {{cannot both conform to and suppress conformance to 'Sendable'}}
   }
 
-  func check<T: Sendable>(_: T) {}
-
-  check(NonSendable()) // expected-warning {{type 'NonSendable' does not conform to the 'Sendable' protocol}}
-  check(NoInference()) // Ok
+  testSendable(NonSendable()) // expected-warning {{type 'NonSendable' does not conform to the 'Sendable' protocol}}
+  testSendable(NoInference()) // Ok
 }
 
 func takesSendable<T: Sendable>(_: T) {}
@@ -91,3 +92,31 @@ extension H: Sendable where T: Sendable, U: Sendable { }
 
 takesSendable(H(t: "", u: 42))
 takesSendable(H(t: "", u: MyValue())) // expected-warning {{type 'MyValue' does not conform to the 'Sendable' protocol}}
+
+@MainActor
+protocol IsolatedP {
+}
+
+@MainActor
+protocol IsolatedSendableP: Sendable {
+}
+
+do {
+  struct S1: ~Sendable, W {
+    // expected-error@-1 {{cannot both conform to and suppress conformance to 'Sendable'}}
+  }
+
+  struct S2: IsolatedP, ~Sendable { // Ok (because isolated protocol is not Sendable unless explicitly stated)
+  }
+
+  struct S3: IsolatedSendableP, ~Sendable {
+    // expected-error@-1 {{cannot both conform to and suppress conformance to 'Sendable'}}
+  }
+
+  @MainActor
+  class IsolatedC: ~Sendable {}
+  // expected-note@-1 {{class 'IsolatedC' explicitly suppresses conformance to 'Sendable' protocol}}
+
+  testSendable(IsolatedC())
+  // expected-warning@-1 {{type 'IsolatedC' does not conform to the 'Sendable' protocol}}
+}