Refactor pull_var_clause's API to make it less tedious to extend.

In commit 1d97c19a0f748e94 and later c1d9579dd8bf3c92, we extended
pull_var_clause's API by adding enum-type arguments.  That's sort of a pain
to maintain, though, because it means every time we add a new behavior we
must touch every last one of the call sites, even if there's a reasonable
default behavior that most of them could use.  Let's switch over to using a
bitmask of flags, instead; that seems more maintainable and might save a
nanosecond or two as well.  This commit changes no behavior in itself,
though I'm going to follow it up with one that does add a new behavior.

In passing, remove flatten_tlist(), which has not been used since 9.1
and would otherwise need the same API changes.

Removing these enums means that optimizer/tlist.h no longer needs to
depend on optimizer/var.h.  Changing that caused a number of C files to
need addition of #include "optimizer/var.h" (probably we can thank old
runs of pgrminclude for that); but on balance it seems like a good change
anyway.

1 files changed, 8 insertions, 7 deletions

diff --git a/src/backend/optimizer/plan/setrefs.c b/src/backend/optimizer/plan/setrefs.c
index 5e949850646..aa2c3084fc8 100644
--- a/src/backend/optimizer/plan/setrefs.c
+++ b/src/backend/optimizer/plan/setrefs.c
@@ -1641,12 +1641,12 @@ set_join_references(PlannerInfo *root, Join *join, int rtoffset)
  *
  * In most cases, we have to match up individual Vars in the tlist and
  * qual expressions with elements of the subplan's tlist (which was
- * generated by flatten_tlist() from these selfsame expressions, so it
- * should have all the required variables).  There is an important exception,
- * however: GROUP BY and ORDER BY expressions will have been pushed into the
- * subplan tlist unflattened.  If these values are also needed in the output
- * then we want to reference the subplan tlist element rather than recomputing
- * the expression.
+ * generated by flattening these selfsame expressions, so it should have all
+ * the required variables).  There is an important exception, however:
+ * depending on where we are in the plan tree, sort/group columns may have
+ * been pushed into the subplan tlist unflattened.  If these values are also
+ * needed in the output then we want to reference the subplan tlist element
+ * rather than recomputing the expression.
  */
 static void
 set_upper_references(PlannerInfo *root, Plan *plan, int rtoffset)
@@ -2129,7 +2129,8 @@ fix_join_expr_mutator(Node *node, fix_join_expr_context *context)
  *
  * An error is raised if no matching var can be found in the subplan tlist
  * --- so this routine should only be applied to nodes whose subplans'
- * targetlists were generated via flatten_tlist() or some such method.
+ * targetlists were generated by flattening the expressions used in the
+ * parent node.
  *
  * If itlist->has_non_vars is true, then we try to match whole subexpressions
  * against elements of the subplan tlist, so that we can avoid recomputing