unified: Mention flattening behavior of 'try?'

Author: asgerf

unified/ql/lib/codeql/unified/internal/dataflow/DataFlowPluginSwift.qll

@@ -38,6 +38,7 @@ private class SwiftDataFlowPlugin extends DataFlowPlugin {
       node2.isResultValue(expr)
       or
       expr.getOperator().(PrefixOperator).getValue() = "try?" and
+      // TODO: preserve the value of some.0 if it is already stored in that
       node1.isResultValue(expr.getOperand()) and
       step.storeName("some.0") and
       node2.isResultValue(expr)

unified/ql/test/library-tests/dataflow/test.swift

@@ -237,3 +237,14 @@ func t26() {
     opt!.0 = source("t26.1")
     sink(opt!.0)  // $ MISSING: hasValueFlow=t26.1
 }
+
+func t27() {
+    func getOptional() throws -> String? {
+        return Optional.some(source("t27.1"))
+    }
+    // TODO: try? should not double-wrap in Optional
+    let x = try? getOptional()
+    if let x {
+        sink(x)  // $ MISSING: hasValueFlow=t27.1
+    }
+}