Refactor JSON output

src/libexpr/value-to-json.hh

@@ -11,4 +11,54 @@ namespace nix {
 void printValueAsJSON(EvalState & state, bool strict,
     Value & v, std::ostream & out, PathSet & context);
 
+void escapeJSON(std::ostream & str, const string & s);
+
+struct JSONObject
+{
+    std::ostream & str;
+    bool first;
+    JSONObject(std::ostream & str) : str(str), first(true)
+    {
+        str << "{";
+    }
+    ~JSONObject()
+    {
+        str << "}";
+    }
+    void attr(const string & s)
+    {
+        if (!first) str << ","; else first = false;
+        escapeJSON(str, s);
+        str << ":";
+    }
+    void attr(const string & s, const string & t)
+    {
+        attr(s);
+        escapeJSON(str, t);
+    }
+};
+
+struct JSONList
+{
+    std::ostream & str;
+    bool first;
+    JSONList(std::ostream & str) : str(str), first(true)
+    {
+        str << "[";
+    }
+    ~JSONList()
+    {
+        str << "]";
+    }
+    void elem()
+    {
+        if (!first) str << ","; else first = false;
+    }
+    void elem(const string & s)
+    {
+        elem();
+        escapeJSON(str, s);
+    }
+};
+
 }