Add test case for rdar://64265821

rdar://64265821 [SR-12985] appears to have been fixed already. Let’s add a test case for it.

Author: ahoppen

validation-test/IDE/crashers_2_fixed/rdar64265821.swift

@@ -0,0 +1,12 @@
+// RUN: %target-swift-ide-test -code-completion -code-completion-token=COMPLETE -source-filename=%s
+
+struct AnyPublisher<T> {
+  public func sink(_: @escaping ((T) -> Void)) -> Void { fatalError() }
+}
+class MyClass {
+  func fetchFile<T>(with: T) -> AnyPublisher<T> { fatalError() }
+  init() {
+    fetchFile(with: #^COMPLETE^#42)
+      .sink { a in var b = a }
+  }
+}