Improve parser's and planner's handling of set-returning functions.

Teach the parser to reject misplaced set-returning functions during parse
analysis using p_expr_kind, in much the same way as we do for aggregates
and window functions (cf commit eaccfded9).  While this isn't complete
(it misses nesting-based restrictions), it's much better than the previous
error reporting for such cases, and it allows elimination of assorted
ad-hoc expression_returns_set() error checks.  We could add nesting checks
later if it seems important to catch all cases at parse time.

There is one case the parser will now throw error for although previous
versions allowed it, which is SRFs in the tlist of an UPDATE.  That never
behaved sensibly (since it's ill-defined which generated row should be
used to perform the update) and it's hard to see why it should not be
treated as an error.  It's a release-note-worthy change though.

Also, add a new Query field hasTargetSRFs reporting whether there are
any SRFs in the targetlist (including GROUP BY/ORDER BY expressions).
The parser can now set that basically for free during parse analysis,
and we can use it in a number of places to avoid expression_returns_set
searches.  (There will be more such checks soon.)  In some places, this
allows decontorting the logic since it's no longer expensive to check for
SRFs in the tlist --- so I made the checks parallel to the handling of
hasAggs/hasWindowFuncs wherever it seemed appropriate.

catversion bump because adding a Query field changes stored rules.

Andres Freund and Tom Lane

Discussion: <24639.1473782855@sss.pgh.pa.us>

1 files changed, 2 insertions, 1 deletions

diff --git a/src/include/parser/parse_node.h b/src/include/parser/parse_node.h
index e3e359c0219..66335863db0 100644
--- a/src/include/parser/parse_node.h
+++ b/src/include/parser/parse_node.h
@@ -27,7 +27,7 @@
  * by extension code that might need to call transformExpr().  The core code
  * will not enforce any context-driven restrictions on EXPR_KIND_OTHER
  * expressions, so the caller would have to check for sub-selects, aggregates,
- * and window functions if those need to be disallowed.
+ * window functions, SRFs, etc if those need to be disallowed.
  */
 typedef enum ParseExprKind
 {
@@ -150,6 +150,7 @@ struct ParseState
 	Node	   *p_value_substitute;		/* what to replace VALUE with, if any */
 	bool		p_hasAggs;
 	bool		p_hasWindowFuncs;
+	bool		p_hasTargetSRFs;
 	bool		p_hasSubLinks;
 	bool		p_hasModifyingCTE;
 	bool		p_is_insert;