[Concurrency] Allow nonisolated(nonsending) inference on properties with async getters

When `NonisolatedNonsendingByDefault` is enabled it should infer
`nonisolated(nonsending)` for both async functions and storage as
specified by the proposal.

(cherry picked from commit 8a9bbd5)

Author: xedin

lib/Sema/TypeCheckConcurrency.cpp

@@ -4951,10 +4951,11 @@ getIsolationFromAttributes(const Decl *decl, bool shouldDiagnose = true,
     // return caller isolation inheriting.
     if (decl->getASTContext().LangOpts.hasFeature(
             Feature::NonisolatedNonsendingByDefault)) {
-      if (auto *func = dyn_cast<AbstractFunctionDecl>(decl);
-          func && func->hasAsync() &&
-          func->getModuleContext() == decl->getASTContext().MainModule) {
-        return ActorIsolation::forCallerIsolationInheriting();
+      if (auto *value = dyn_cast<ValueDecl>(decl)) {
+        if (value->isAsync() &&
+            value->getModuleContext() == decl->getASTContext().MainModule) {
+          return ActorIsolation::forCallerIsolationInheriting();
+        }
       }
     }
 
@@ -5815,11 +5816,9 @@ computeDefaultInferredActorIsolation(ValueDecl *value) {
         return *result;
   }
 
-  // If we have an async function... by default we inherit isolation.
+  // If we have an async function or storage... by default we inherit isolation.
   if (ctx.LangOpts.hasFeature(Feature::NonisolatedNonsendingByDefault)) {
-    if (auto *func = dyn_cast<AbstractFunctionDecl>(value);
-        func && func->hasAsync() &&
-        func->getModuleContext() == ctx.MainModule) {
+    if (value->isAsync() && value->getModuleContext() == ctx.MainModule) {
       return {
           {ActorIsolation::forCallerIsolationInheriting(), {}}, nullptr, {}};
     }
@@ -6232,11 +6231,8 @@ static InferredActorIsolation computeActorIsolation(Evaluator &evaluator,
       if (selfTypeIsolation.isolation) {
         auto isolation = selfTypeIsolation.isolation;
 
-        if (auto *func = dyn_cast<AbstractFunctionDecl>(value);
-            ctx.LangOpts.hasFeature(
-                Feature::NonisolatedNonsendingByDefault) &&
-            func && func->hasAsync() &&
-            func->getModuleContext() == ctx.MainModule &&
+        if (ctx.LangOpts.hasFeature(Feature::NonisolatedNonsendingByDefault) &&
+            value->isAsync() && value->getModuleContext() == ctx.MainModule &&
             isolation.isNonisolated()) {
           isolation = ActorIsolation::forCallerIsolationInheriting();
         }

test/SILGen/nonisolated_inherits_isolation.swift

@@ -151,3 +151,21 @@ class MainActorKlass {
     await unspecifiedAsyncUse(n)
   }
 }
+
+struct TestVarUse {
+  var test: Int {
+    // CHECK-LABEL: sil hidden [ossa] @$s30nonisolated_inherits_isolation10TestVarUseV4testSivg : $@convention(method) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, TestVarUse) -> Int
+    get async {
+      42
+    }
+  }
+}
+
+// CHECK-LABEL: sil hidden [ossa] @$s30nonisolated_inherits_isolation12testUseOfVar1tyAA04TestgE0V_tYaF : $@convention(thin) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, TestVarUse) -> ()
+// CHECK: bb0([[ISOLATION:%.*]] : @guaranteed $Optional<any Actor>, [[BASE:%.*]] : $TestVarUse)
+// CHECK:   [[GETTER:%.*]] = function_ref @$s30nonisolated_inherits_isolation10TestVarUseV4testSivg : $@convention(method) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, TestVarUse) -> Int
+// CHECK:   {{.*}} = apply [[GETTER]]([[ISOLATION]], [[BASE]])
+// CHECK: } // end sil function '$s30nonisolated_inherits_isolation12testUseOfVar1tyAA04TestgE0V_tYaF'
+func testUseOfVar(t: TestVarUse) async {
+  _ = await t.test
+}