Allow polymorphic aggregates to have non-polymorphic state data types.

Before 9.4, such an aggregate couldn't be declared, because its final
function would have to have polymorphic result type but no polymorphic
argument, which CREATE FUNCTION would quite properly reject.  The
ordered-set-aggregate patch found a workaround: allow the final function
to be declared as accepting additional dummy arguments that have types
matching the aggregate's regular input arguments.  However, we failed
to notice that this problem applies just as much to regular aggregates,
despite the fact that we had a built-in regular aggregate array_agg()
that was known to be undeclarable in SQL because its final function
had an illegal signature.  So what we should have done, and what this
patch does, is to decouple the extra-dummy-arguments behavior from
ordered-set aggregates and make it generally available for all aggregate
declarations.  We have to put this into 9.4 rather than waiting till
later because it slightly alters the rules for declaring ordered-set
aggregates.

The patch turned out a bit bigger than I'd hoped because it proved
necessary to record the extra-arguments option in a new pg_aggregate
column.  I'd thought we could just look at the final function's pronargs
at runtime, but that didn't work well for variadic final functions.
It's probably just as well though, because it simplifies life for pg_dump
to record the option explicitly.

While at it, fix array_agg() to have a valid final-function signature,
and add an opr_sanity test to notice future deviations from polymorphic
consistency.  I also marked the percentile_cont() aggregates as not
needing extra arguments, since they don't.

1 files changed, 26 insertions, 22 deletions

diff --git a/src/backend/executor/nodeAgg.c b/src/backend/executor/nodeAgg.c
index d60845bcd34..186c319a3a2 100644
--- a/src/backend/executor/nodeAgg.c
+++ b/src/backend/executor/nodeAgg.c
@@ -37,11 +37,12 @@
  *
  *	  Ordered-set aggregates are treated specially in one other way: we
  *	  evaluate any "direct" arguments and pass them to the finalfunc along
- *	  with the transition value.  In addition, NULL placeholders are
- *	  provided to match the remaining finalfunc arguments, which correspond
- *	  to the aggregated expressions.  (These arguments have no use at
- *	  runtime, but may be needed to allow resolution of a polymorphic
- *	  aggregate's result type.)
+ *	  with the transition value.
+ *
+ *	  A finalfunc can have additional arguments beyond the transvalue and
+ *	  any "direct" arguments, corresponding to the input arguments of the
+ *	  aggregate.  These are always just passed as NULL.  Such arguments may be
+ *	  needed to allow resolution of a polymorphic aggregate's result type.
  *
  *	  We compute aggregate input expressions and run the transition functions
  *	  in a temporary econtext (aggstate->tmpcontext).  This is reset at
@@ -151,6 +152,14 @@ typedef struct AggStatePerAggData
 	 */
 	int			numTransInputs;
 
+	/*
+	 * Number of arguments to pass to the finalfn.	This is always at least 1
+	 * (the transition state value) plus any ordered-set direct args. If the
+	 * finalfn wants extra args then we pass nulls corresponding to the
+	 * aggregated input columns.
+	 */
+	int			numFinalArgs;
+
 	/* Oids of transfer functions */
 	Oid			transfn_oid;
 	Oid			finalfn_oid;	/* may be InvalidOid */
@@ -797,6 +806,8 @@ finalize_aggregate(AggState *aggstate,
 	/*
 	 * Evaluate any direct arguments.  We do this even if there's no finalfn
 	 * (which is unlikely anyway), so that side-effects happen as expected.
+	 * The direct arguments go into arg positions 1 and up, leaving position 0
+	 * for the transition state value.
 	 */
 	i = 1;
 	foreach(lc, peraggstate->aggrefstate->aggdirectargs)
@@ -816,19 +827,7 @@ finalize_aggregate(AggState *aggstate,
 	 */
 	if (OidIsValid(peraggstate->finalfn_oid))
 	{
-		int			numFinalArgs;
-
-		/*
-		 * Identify number of arguments being passed to the finalfn.  For a
-		 * plain agg it's just one (the transition state value).  For
-		 * ordered-set aggs we also pass the direct argument(s), plus nulls
-		 * corresponding to the aggregate-input columns.
-		 */
-		if (AGGKIND_IS_ORDERED_SET(peraggstate->aggref->aggkind))
-			numFinalArgs = peraggstate->numArguments + 1;
-		else
-			numFinalArgs = 1;
-		Assert(i <= numFinalArgs);
+		int			numFinalArgs = peraggstate->numFinalArgs;
 
 		/* set up aggstate->curperagg for AggGetAggref() */
 		aggstate->curperagg = peraggstate;
@@ -844,12 +843,11 @@ finalize_aggregate(AggState *aggstate,
 		anynull |= pergroupstate->transValueIsNull;
 
 		/* Fill any remaining argument positions with nulls */
-		while (i < numFinalArgs)
+		for (; i < numFinalArgs; i++)
 		{
 			fcinfo.arg[i] = (Datum) 0;
 			fcinfo.argnull[i] = true;
 			anynull = true;
-			i++;
 		}
 
 		if (fcinfo.flinfo->fn_strict && anynull)
@@ -1776,12 +1774,18 @@ ExecInitAgg(Agg *node, EState *estate, int eflags)
 		numInputs = list_length(aggref->args);
 		peraggstate->numInputs = numInputs;
 
-		/* Detect how many columns to pass to the transfn */
+		/* Detect how many arguments to pass to the transfn */
 		if (AGGKIND_IS_ORDERED_SET(aggref->aggkind))
 			peraggstate->numTransInputs = numInputs;
 		else
 			peraggstate->numTransInputs = numArguments;
 
+		/* Detect how many arguments to pass to the finalfn */
+		if (aggform->aggfinalextra)
+			peraggstate->numFinalArgs = numArguments + 1;
+		else
+			peraggstate->numFinalArgs = numDirectArgs + 1;
+
 		/* resolve actual type of transition state, if polymorphic */
 		aggtranstype = resolve_aggregate_transtype(aggref->aggfnoid,
 												   aggform->aggtranstype,
@@ -1792,7 +1796,7 @@ ExecInitAgg(Agg *node, EState *estate, int eflags)
 		build_aggregate_fnexprs(inputTypes,
 								numArguments,
 								numDirectArgs,
-								AGGKIND_IS_ORDERED_SET(aggref->aggkind),
+								peraggstate->numFinalArgs,
 								aggref->aggvariadic,
 								aggtranstype,
 								aggref->aggtype,