MDEV-6109: EXPLAIN JSON10.1-explain-json

- First code, "EXPLAIN FORMAT=JSON stmt" and "ANALYZE FORMAT=JSON stmt"
  work for basic queries.  Complex constructs (e.g subqueries, etc) not
  yet supported.
- No test infrastructure yet

1 files changed, 43 insertions, 0 deletions

diff --git a/sql/my_json_writer.h b/sql/my_json_writer.h
new file mode 100644
index 00000000000..403d7e0688c
--- /dev/null
+++ b/sql/my_json_writer.h
@@ -0,0 +1,43 @@
+/* Todo: SkySQL copyrights */
+
+class Json_writer
+{
+public:
+  /* Add a member. We must be in an object. */
+  Json_writer& add_member(const char *name);
+  
+  /* Add atomic values */
+  void add_ll(longlong val);
+  void add_str(const char* val);
+  void add_str(const String &str);
+  void add_double(double val);
+  void add_bool(bool val);
+  
+  /* Start a child object */
+  void start_object();
+  void start_array();
+
+  void end_object();
+  void end_array();
+  
+  Json_writer() : 
+    indent_level(0), document_start(true), element_started(false), 
+    first_child(true)
+  {}
+private:
+  // stack of (name, bool is_object_or_array) elements.
+  int indent_level;
+  enum { INDENT_SIZE = 2 };
+  
+  bool document_start;
+  bool element_started;
+  bool first_child;
+
+  void append_indent();
+  void start_element();
+
+  //const char *new_member_name;
+public:
+  String output;
+};
+