unified: Simplify plugin code

Author: asgerf

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

@@ -31,32 +31,23 @@ private class SwiftDataFlowPlugin extends DataFlowPlugin {
     )
     or
     exists(UnaryExpr expr |
-      expr.getOperator().(PostfixOperator).getValue() = "!" and
-      node1.isResultValue(expr.getOperand()) and
-      (step.readName("some.0") or step.taint()) and
-      node2.isResultValue(expr)
+      expr.getOperator().(PostfixOperator).getValue() = "!"
       or
-      expr.getOperator().(PrefixOperator).getValue() = ["try", "try!", "await"] and
+      expr.getOperator().(PrefixOperator).getValue() = ["try", "try!", "try?", "await"]
+    |
       node1.isResultValue(expr.getOperand()) and
       step.value() and
       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)
     )
     or
     exists(TypeCastExpr expr |
-      // The `as?` type cast boxes the incoming value in Optional depending on whether the type cast succeeded
-      expr.getOperator().getValue() = "as?" and
-      node1.isResultValue(expr.getExpr()) and
-      step.storeName("some.0") and
-      node2.isResultValue(expr)
-      or
-      // Safe upcast conversion ("as") and downcast-or-throw ("as!") propagate the value directly
-      expr.getOperator().getValue() = ["as", "as!"] and
+      // Type-cast operators:
+      // - "as": Safe upcast conversion
+      // - "as?": Wrap in Optional<T> if cast succeeds
+      // - "as!": Throw if cast fails
+      //
+      // Since we bypass Optional<T> content, we model all of these as value steps.
+      expr.getOperator().getValue() = ["as", "as?", "as!"] and
       node1.isResultValue(expr.getExpr()) and
       step.value() and
       node2.isResultValue(expr)