[Concurrency] Downgrade non-Sendable type captures to warnings if closure is in @preconcurrency context

The original check examined only the immediate closure, but it's
possible that the closure happens to be in a preconcurrency context
which also requires a downgrade.

Resolves: rdar://148996589

Author: xedin

lib/Sema/TypeCheckConcurrency.cpp

@@ -2924,8 +2924,10 @@ namespace {
       auto *explicitClosure = dyn_cast_or_null<ClosureExpr>(closure);
 
       bool preconcurrency = false;
-      if (explicitClosure) {
-        preconcurrency = explicitClosure->isIsolatedByPreconcurrency();
+      if (closure) {
+        preconcurrency =
+            getActorIsolationOfContext(closure, getClosureActorIsolation)
+                .preconcurrency();
       }
 
       for (const auto &capture : localFunc.getCaptureInfo().getCaptures()) {

test/Concurrency/sendable_checking_captures_swift6.swift

@@ -50,3 +50,31 @@ do {
     }
   }
 }
+
+func use(_ closure: @autoclosure () -> Any) {
+}
+
+do {
+  class C {
+    @preconcurrency static func f(_: @escaping @Sendable () -> Void) {}
+  }
+
+  class SelfCapture { // expected-note 5 {{class 'SelfCapture' does not conform to the 'Sendable' protocol}}
+    func fooDirect() {
+      C.f {
+        use(self)
+        // expected-warning@-1 {{capture of 'self' with non-sendable type 'SelfCapture' in a '@Sendable' closure}}
+        // expected-warning@-2 {{implicit capture of 'self' requires that 'SelfCapture' conforms to 'Sendable'}}
+      }
+    }
+
+    func fooThroughClosure() {
+      C.f {
+        { use(self) }()
+        // expected-warning@-1 {{capture of 'self' with non-sendable type 'SelfCapture' in a '@Sendable' closure}}
+        // expected-warning@-2 {{capture of 'self' with non-sendable type 'SelfCapture' in an isolated closure}}
+        // expected-warning@-3 {{implicit capture of 'self' requires that 'SelfCapture' conforms to 'Sendable'}}
+      }
+    }
+  }
+}

test/Concurrency/sendable_objc_attr_in_type_context_swift6.swift

@@ -86,6 +86,10 @@ void doSomethingConcurrently(__attribute__((noescape)) void SWIFT_SENDABLE (^blo
 -(void) testWithCompletion: (void (^)(void)) completion;
 @end
 
+@interface TestSelfCapture : NSObject
++ (void)doWithCompletion:(void(^)(void)) completion;
+@end
+
 #pragma clang assume_nonnull end
 
 //--- main.swift
@@ -219,3 +223,25 @@ extension TestDR {
   @_dynamicReplacement(for: test(completion:))
   func __replaceObjCFunc(_: @escaping () -> Void) {} // Ok
 }
+
+class SelfCapture { // expected-note 5 {{class 'SelfCapture' does not conform to the 'Sendable' protocol}}
+  static func use(_ closure: @autoclosure () -> Any) {
+  }
+  
+  func testDirect() {
+    TestSelfCapture.do {
+      Self.use(self)
+      // expected-warning@-1 {{capture of 'self' with non-sendable type 'SelfCapture' in a '@Sendable' closure}}
+      // expected-warning@-2 {{implicit capture of 'self' requires that 'SelfCapture' conforms to 'Sendable'}}
+    }
+  }
+
+  func testThroughClosure() {
+    TestSelfCapture.do {
+      let _ = { Self.use(self) }()
+      // expected-warning@-1 {{capture of 'self' with non-sendable type 'SelfCapture' in a '@Sendable' closure}}
+      // expected-warning@-2 {{capture of 'self' with non-sendable type 'SelfCapture' in an isolated closure}}
+      // expected-warning@-3 {{implicit capture of 'self' requires that 'SelfCapture' conforms to 'Sendable'}}
+    }
+  }
+}