Future-proof the recursion inside ExecShutdownNode().

The API contract for planstate_tree_walker() callbacks is that they
take a PlanState pointer and a context pointer.  Somebody figured
they could save a couple lines of code by ignoring that, and passing
ExecShutdownNode itself as the walker even though it has but one
argument.  Somewhat remarkably, we've gotten away with that so far.
However, it seems clear that the upcoming C2x standard means to
forbid such cases, and compilers that actively break such code
likely won't be far behind.  So spend the extra few lines of code
to do it honestly with a separate walker function.

In HEAD, we might as well go further and remove ExecShutdownNode's
useless return value.  I left that as-is in back branches though,
to forestall complaints about ABI breakage.

Back-patch, with the thought that this might become of practical
importance before our stable branches are all out of service.
It doesn't seem to be fixing any live bug on any currently known
platform, however.

Discussion: https://postgr.es/m/208054.1663534665@sss.pgh.pa.us

diff --git a/src/backend/executor/execProcnode.c b/src/backend/executor/execProcnode.c
index 01b7b926bf705dbaf0076c7bcdf2dfdc0022d1cb..19dd9004afe930d51963eaa48b43989eaca623fd 100644 (file)
--- a/src/backend/executor/execProcnode.c
+++ b/src/backend/executor/execProcnode.c
@@ -119,6 +119,7 @@
 
 static TupleTableSlot *ExecProcNodeFirst(PlanState *node);
 static TupleTableSlot *ExecProcNodeInstr(PlanState *node);
+static bool ExecShutdownNode_walker(PlanState *node, void *context);
 
 
 /* ------------------------------------------------------------------------
@@ -749,6 +750,12 @@ ExecEndNode(PlanState *node)
  */
 bool
 ExecShutdownNode(PlanState *node)
+{
+   return ExecShutdownNode_walker(node, NULL);
+}
+
+static bool
+ExecShutdownNode_walker(PlanState *node, void *context)
 {
    if (node == NULL)
        return false;
@@ -768,7 +775,7 @@ ExecShutdownNode(PlanState *node)
    if (node->instrument && node->instrument->running)
        InstrStartNode(node->instrument);
 
-   planstate_tree_walker(node, ExecShutdownNode, NULL);
+   planstate_tree_walker(node, ExecShutdownNode_walker, context);
 
    switch (nodeTag(node))
    {