[Concurrency] NonisolatedNonsendingByDefault: Extend nonisolated(nonsending) to _openExistential

`_openExistential` is type-checked in a special way which
means that we need to explicitly inject `nonisolated(nonsending)`
isolation when forming a reference to this builtin.

(cherry picked from commit 358869f)

Author: xedin

lib/Sema/TypeOfReference.cpp

@@ -2374,20 +2374,36 @@ static DeclReferenceType getTypeOfReferenceWithSpecialTypeCheckingSemantics(
         CS.getConstraintLocator(locator, ConstraintLocator::ThrownErrorType),
         0);
     FunctionType::Param bodyArgs[] = {FunctionType::Param(openedTy)};
+
+    auto bodyParamIsolation = FunctionTypeIsolation::forNonIsolated();
+    if (CS.getASTContext().LangOpts.hasFeature(
+            Feature::NonisolatedNonsendingByDefault)) {
+      bodyParamIsolation = FunctionTypeIsolation::forNonIsolatedCaller();
+    }
+
     auto bodyClosure = FunctionType::get(bodyArgs, result,
                                          FunctionType::ExtInfoBuilder()
                                              .withNoEscape(true)
                                              .withThrows(true, thrownError)
+                                             .withIsolation(bodyParamIsolation)
                                              .withAsync(true)
                                              .build());
     FunctionType::Param args[] = {
       FunctionType::Param(existentialTy),
       FunctionType::Param(bodyClosure, CS.getASTContext().getIdentifier("do")),
     };
+
+    auto openExistentialIsolation = FunctionTypeIsolation::forNonIsolated();
+    if (CS.getASTContext().LangOpts.hasFeature(
+            Feature::NonisolatedNonsendingByDefault)) {
+      openExistentialIsolation = FunctionTypeIsolation::forNonIsolatedCaller();
+    }
+
     auto refType = FunctionType::get(args, result,
                                      FunctionType::ExtInfoBuilder()
                                          .withNoEscape(false)
                                          .withThrows(true, thrownError)
+                                         .withIsolation(openExistentialIsolation)
                                          .withAsync(true)
                                          .build());
     return {refType, refType, refType, refType, Type()};

test/Concurrency/attr_execution/attr_execution.swift

@@ -81,6 +81,20 @@ func testClosure() {
   }
 }
 
+protocol P {
+}
+
+func open<T: P>(_: T) async {}
+
+// CHECK-LABEL: sil hidden [ossa] @$s14attr_execution19testOpenExistential11existentialyAA1P_p_tYaF : $@convention(thin) @async (@sil_isolated @sil_implicit_leading_param @guaranteed Optional<any Actor>, @in_guaranteed any P) -> ()
+// CHECK: bb0([[ISOLATION:%.*]] : @guaranteed $Optional<any Actor>, [[EXISTENTIAL:%.*]] : $*any P):
+// CHECK: [[OPEN_REF:%.*]] = function_ref @$s14attr_execution4openyyxYaAA1PRzlF
+// CHECK: apply [[OPEN_REF]]<@opened("{{.*}}", any P) Self>([[ISOLATION]], {{.*}})
+// CHECK: } // end sil function '$s14attr_execution19testOpenExistential11existentialyAA1P_p_tYaF'
+func testOpenExistential(existential: any P) async {
+  await _openExistential(existential, do: open)
+}
+
 func testWithoutActuallyEscaping(_ f: () async -> ()) async {
   // CHECK-LABEL: // closure #1 in testWithoutActuallyEscaping(_:)
   // CHECK-NEXT: // Isolation: caller_isolation_inheriting