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, 129 insertions, 0 deletions

diff --git a/sql/my_json_writer.cc b/sql/my_json_writer.cc
new file mode 100644
index 00000000000..206597da59e
--- /dev/null
+++ b/sql/my_json_writer.cc
@@ -0,0 +1,129 @@
+/* Todo: SkySQL copyrights */
+
+#include <my_global.h>
+#include "sql_priv.h"
+#include "sql_string.h"
+
+#include "my_json_writer.h"
+
+void Json_writer::append_indent()
+{
+  if (!document_start)
+    output.append('\n');
+  for (int i=0; i< indent_level; i++)
+    output.append(' ');
+}
+
+void Json_writer::start_object()
+{
+  if (!element_started)
+    start_element();
+
+  output.append("{");
+  indent_level+=INDENT_SIZE;
+  first_child=true;
+  element_started= false;
+  document_start= false;
+}
+
+void Json_writer::start_array()
+{
+  if (!element_started)
+    start_element();
+
+  output.append("[");
+  indent_level+=INDENT_SIZE;
+  first_child=true;
+  element_started= false;
+  document_start= false;
+}
+
+
+void Json_writer::end_object()
+{
+  indent_level-=INDENT_SIZE;
+  if (!first_child)
+    append_indent();
+  output.append("}");
+}
+
+
+void Json_writer::end_array()
+{
+  indent_level-=INDENT_SIZE;
+  if (!first_child)
+    append_indent();
+  output.append("]");
+}
+
+
+Json_writer& Json_writer::add_member(const char *name)
+{
+  // assert that we are in an object
+  DBUG_ASSERT(!element_started);
+  start_element();
+
+  output.append('"');
+  output.append(name);
+  output.append("\": ");
+  return *this;
+}
+
+
+void Json_writer::start_element()
+{
+  element_started= true;
+
+  if (first_child)
+    first_child= false;
+  else
+    output.append(',');
+
+  append_indent();
+}
+
+void Json_writer::add_ll(longlong val)
+{
+  if (!element_started)
+    start_element();
+
+  char buf[64];
+  my_snprintf(buf, sizeof(buf), "%ld", val);
+  output.append(buf);
+  element_started= false;
+}
+
+
+void Json_writer::add_double(double val)
+{
+  if (!element_started)
+    start_element();
+
+  char buf[64];
+  my_snprintf(buf, sizeof(buf), "%lf", val);
+  output.append(buf);
+  element_started= false;
+}
+
+
+void Json_writer::add_str(const char *str)
+{
+  if (!element_started)
+    start_element();
+
+  output.append('"');
+  output.append(str);
+  output.append('"');
+  element_started= false;
+}
+
+void Json_writer::add_bool(bool val)
+{
+  add_str(val? "true" : "false");
+}
+
+void Json_writer::add_str(const String &str)
+{
+  add_str(str.ptr());
+}
+