Fix the wrong measure for the change in ExplainState.

The fix made in the commit 6819c84350ea599988440c5c07becfe56c71723a is
not appropriate according to its objective. The correct fix for the
change is translating es->extra as "List *grouping_stack" in the
versions 9.3.6, 9.4.1 and their successors. This secure the binary
comaptibility throughout minor PG versions.

diff --git a/pgsp_explain.c b/pgsp_explain.c
index fa986b8..6bdc6ed 100644 (file)
--- a/pgsp_explain.c
+++ b/pgsp_explain.c
@@ -22,9 +22,17 @@ static void pgspExplainProperty(const char *qlabel, const char *value, bool nume
                                                        ExplainState *es);
 static void pgspExplainJSONLineEnding(ExplainState *es);
 
-/* ExplainState is modified at 9.4.1 and 9.3.6  */
-#if PG_VERSION_NUM >= 90401 || (PG_VERSION_NUM >= 90306 && PG_VERSION_NUM < 90400)
-#define GROUPING_STACK(es) ((es)->extra->groupingstack)
+/*
+ * ExplainState is modified at 9.4.1 and 9.3.6. But the change is for
+ * internal use and to avoid binary-incompatibility not changing the
+ * size of ExplainState. So we can use ExplainState->extra as if it
+ * were grouping_stack safely and should do so. Using ->extra as List*
+ * discards the memory for ExplainStateExtra but it is not a problem
+ * since it is allocated by palloc.
+ */
+#if (PG_VERSION_NUM >= 90401 && PG_VERSION_NUM < 90500) || \
+       (PG_VERSION_NUM >= 90306 && PG_VERSION_NUM < 90400)
+#define GROUPING_STACK(es) (*((List **)(&(es)->extra)))
 #else
 #define GROUPING_STACK(es) ((es)->grouping_stack)
 #endif