From 19b1f25a1209c7af9e73c0e68ba33574a3b4cbb7 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Tue, 23 Jan 2024 09:22:36 +0200
Subject: Add reverse

---
 libbuild2/json.cxx     |  2 ++
 libbuild2/json.hxx     | 20 ++++++++++++-
 libbuild2/parser.cxx   |  1 +
 libbuild2/variable.cxx | 76 ++++++++++++++++++++++++++++++++++++++++++++++++--
 4 files changed, 96 insertions(+), 3 deletions(-)

diff --git a/libbuild2/json.cxx b/libbuild2/json.cxx
index dfa1a07..53f7ae4 100644
--- a/libbuild2/json.cxx
+++ b/libbuild2/json.cxx
@@ -181,6 +181,8 @@ namespace build2
         container_type c; // For exception safety.
         while (*p.next () != event::end_object)
         {
+          // @@ Override duplicates or fail?
+
           string_type n (p.name ());
           json_value v (p);
           v.name = move (n);
diff --git a/libbuild2/json.hxx b/libbuild2/json.hxx
index 6fc633c..9a57b8f 100644
--- a/libbuild2/json.hxx
+++ b/libbuild2/json.hxx
@@ -241,13 +241,31 @@ namespace build2
     // names are ignored.
     //
     int
-      compare (const json_value&, bool ignore_name = false) const;
+    compare (const json_value&, bool ignore_name = false) const;
   };
 
   // Throws invalid_json_output.
   //
   LIBBUILD2_SYMEXPORT void
   serialize (butl::json::buffer_serializer&, const json_value&);
+
+  inline bool
+  operator== (const json_value& x, const json_value& y) {return x.compare (y) == 0;}
+
+  inline bool
+  operator!= (const json_value& x, const json_value& y) {return !(x == y);}
+
+  inline bool
+  operator< (const json_value& x, const json_value& y) {return x.compare (y) < 0;}
+
+  inline bool
+  operator<= (const json_value& x, const json_value& y) {return x.compare (y) <= 0;}
+
+  inline bool
+  operator> (const json_value& x, const json_value& y) {return !(x <= y);}
+
+  inline bool
+  operator>= (const json_value& x, const json_value& y) {return !(x < y);}
 }
 
 #endif // LIBBUILD2_JSON_HXX
diff --git a/libbuild2/parser.cxx b/libbuild2/parser.cxx
index b695018..517f058 100644
--- a/libbuild2/parser.cxx
+++ b/libbuild2/parser.cxx
@@ -5753,6 +5753,7 @@ namespace build2
       n == "dir_paths"      ? ptr (value_traits<dir_paths>::value_type)      :
       n == "names"          ? ptr (value_traits<vector<name>>::value_type)   :
       n == "cmdline"        ? ptr (value_traits<cmdline>::value_type)        :
+      n == "json"           ? ptr (value_traits<json_value>::value_type)     :
 
       nullptr;
   }
diff --git a/libbuild2/variable.cxx b/libbuild2/variable.cxx
index c83d55e..efc1eb2 100644
--- a/libbuild2/variable.cxx
+++ b/libbuild2/variable.cxx
@@ -1743,9 +1743,81 @@ namespace build2
   */
 
   static names_view
-  json_reverse (const value&, names& storage, bool)
+  json_reverse (const value& x, names& ns, bool)
   {
-    return names_view (storage); // @@ TODO
+    const json_value& v (x.as<json_value> ());
+
+    switch (v.type)
+    {
+    case json_type::null:
+      {
+        // @@ Hm, it would be nice if this somehow got mapped to [null]/empty
+        //    but still be round-trippable to JSON null. Perhaps via type
+        //    hint?
+        //
+        ns.push_back (name ("null"));
+        break;
+      }
+    case json_type::boolean:
+      {
+        ns.push_back (name (v.boolean ? "true" : "false"));
+        break;
+      }
+    case json_type::signed_number:
+      {
+        ns.push_back (value_traits<int64_t>::reverse (v.signed_number));
+        break;
+      }
+    case json_type::unsigned_number:
+      {
+        ns.push_back (value_traits<uint64_t>::reverse (v.unsigned_number));
+        break;
+      }
+    case json_type::string:
+        // @@ Hm, it would be nice if this somehow got mapped to unquoted
+        //    string but still be round-trippable to JSON null. Perhaps via
+        //    type hint?
+        //
+        // @@ If not, optimize for case where no escaping/quoting required?
+        //
+    case json_type::array:
+    case json_type::object:
+      {
+        // Serialize as JSON output.
+        //
+        string o;
+
+#ifndef BUILD2_BOOTSTRAP
+        using namespace butl::json;
+
+        try
+        {
+          // Disable pretty-printing so that the output is all on the same
+          // line. While it's not going to be easy to read for larger JSON
+          // outputs, it will fit better into the existing model where none of
+          // the value representations use formatting newlines. If a pretty-
+          // printed representation is required, then the @@ function can be
+          // used to obtain it.
+          //
+          buffer_serializer s (o, 0 /* indentation */);
+          serialize (s, v);
+        }
+        catch (const invalid_json_output& e)
+        {
+          // @@ How can we communicate event, offset? But for that to be
+          //    useful we would also need to somehow also dump the value.
+          //
+          fail << "invalid json value: " << e;
+        }
+#else
+        fail << "json serialization requested during bootstrap";
+#endif
+        ns.push_back (name (move (o)));
+        break;
+      }
+    }
+
+    return ns;
   }
 
   static int
-- 
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