[Concurrency] Add basic tests for function isolation extraction.

Author: hborla

test/Concurrency/isolated_any.swift

@@ -83,3 +83,16 @@ func extractFunctionIsolation(_ fn: @isolated(any) @escaping () async -> Void) {
   let _: (any Actor)? = extractIsolation(myActor.asyncThrowsActorFunction)
   let _: (any Actor)? = extractIsolation(myActor.actorFunctionWithArgs(value:))
 }
+
+func extractFunctionIsolationExpr(
+  _ fn1: @isolated(any) @escaping () async -> Void,
+  _ fn2: @isolated(any) @escaping (Int, String) -> Bool
+) {
+  let _: (any Actor)? = fn1.isolation
+  let _: (any Actor)? = fn2.isolation
+
+  // Only `@isolated(any)` functions have `.isolation`
+  let myActor = A()
+  let _: (any Actor)? = myActor.asyncActorFunction.isolation // expected-error {{value of type '@Sendable () async -> ()' has no member 'isolation'}}
+  let _: (any Actor)? = globalNonisolatedFunction.isolation // expected-error {{value of type '@Sendable () -> ()' has no member 'isolation'}}
+}

test/SILGen/isolated_any.swift

@@ -452,3 +452,17 @@ extension MyActor {
 func testEraseAsyncActorIsolatedPartialApplication(a: MyActor) {
   takeAsyncIsolatedAny(fn: a.asyncAction)
 }
+
+/*-- Isolation extraction --*/
+
+// CHECK-LABEL: sil hidden [ossa] @$s4test16extractIsolation2fnScA_pSgyyYAc_tF
+// CHECK: [[FN:%.*]] = copy_value %0 : $@isolated(any) @callee_guaranteed () -> ()
+// CHECK-NEXT: [[FN_BORROW:%.*]] = begin_borrow [[FN]] : $@isolated(any) @callee_guaranteed () -> ()
+// CHECK-NEXT: [[ISOLATION:%.*]] = function_extract_isolation [[FN_BORROW]] : $@isolated(any) @callee_guaranteed () -> ()
+// CHECK-NEXT: [[RESULT:%.*]] = copy_value [[ISOLATION]] : $Optional<any Actor>
+// CHECK-NEXT: end_borrow [[FN_BORROW]] : $@isolated(any) @callee_guaranteed () -> ()
+// CHECK-NEXT: destroy_value [[FN]] : $@isolated(any) @callee_guaranteed () -> ()
+// CHECK-NEXT: return [[RESULT]] : $Optional<any Actor>
+func extractIsolation(fn: @escaping @isolated(any) () -> Void) -> (any Actor)? {
+  fn.isolation
+}