DPL Analysis: Expressions <-> JSON

* add serialization/deserialization support for expressions
* add test

Author: aalkin

Framework/Core/CMakeLists.txt

@@ -143,6 +143,7 @@ o2_add_library(Framework
                        src/Array2D.cxx
                        src/Variant.cxx
                        src/VariantJSONHelpers.cxx
+                       src/ExpressionJSONHelpers.cxx
                        src/VariantPropertyTreeHelpers.cxx
                        src/WorkflowCustomizationHelpers.cxx
                        src/WorkflowHelpers.cxx

Framework/Core/include/Framework/ExpressionJSONHelpers.h

@@ -0,0 +1,23 @@
+// Copyright 2019-2025 CERN and copyright holders of ALICE O2.
+// See https://alice-o2.web.cern.ch/copyright for details of the copyright holders.
+// All rights not expressly granted are reserved.
+//
+// This software is distributed under the terms of the GNU General Public
+// License v3 (GPL Version 3), copied verbatim in the file "COPYING".
+//
+// In applying this license CERN does not waive the privileges and immunities
+// granted to it by virtue of its status as an Intergovernmental Organization
+// or submit itself to any jurisdiction.
+#ifndef FRAMEWORK_EXPRESSIONJSONHELPERS_H
+#define FRAMEWORK_EXPRESSIONJSONHELPERS_H
+
+#include "Framework/Expressions.h"
+
+namespace o2::framework {
+struct ExpressionJSONHelpers {
+  static std::unique_ptr<expressions::Node> read(std::istream& s);
+  static void write(std::ostream& o, expressions::Node* n);
+};
+}
+
+#endif // FRAMEWORK_EXPRESSIONJSONHELPERS_H

Framework/Core/include/Framework/Expressions.h

@@ -110,6 +110,8 @@ std::string upcastTo(atype::type f);
 
 /// An expression tree node corresponding to a literal value
 struct LiteralNode {
+  using var_t = LiteralValue::stored_type;
+
   LiteralNode()
     : value{-1},
       type{atype::INT32}
@@ -120,7 +122,12 @@ struct LiteralNode {
   {
   }
 
-  using var_t = LiteralValue::stored_type;
+  LiteralNode(var_t v, atype::type t)
+    : value{v},
+      type{t}
+  {
+  }
+
   var_t value;
   atype::type type = atype::NA;
 };
@@ -617,6 +624,11 @@ inline Node ncfg(T defaultValue, std::string path)
 struct Filter {
   Filter() = default;
 
+  Filter(std::unique_ptr<Node>&& ptr)
+  {
+    node = std::move(ptr);
+  }
+
   Filter(Node&& node_) : node{std::make_unique<Node>(std::forward<Node>(node_))}
   {
     (void)designateSubtrees(node.get());