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, 30 insertions, 3 deletions

diff --git a/src/backend/executor/nodeWindowAgg.c b/src/backend/executor/nodeWindowAgg.c
index 2fcc630a925..40a925331c9 100644
--- a/src/backend/executor/nodeWindowAgg.c
+++ b/src/backend/executor/nodeWindowAgg.c
@@ -116,6 +116,8 @@ typedef struct WindowStatePerAggData
 	FmgrInfo	invtransfn;
 	FmgrInfo	finalfn;
 
+	int			numFinalArgs;	/* number of arguments to pass to finalfn */
+
 	/*
 	 * initial value from pg_aggregate entry
 	 */
@@ -557,14 +559,28 @@ finalize_windowaggregate(WindowAggState *winstate,
 	 */
 	if (OidIsValid(peraggstate->finalfn_oid))
 	{
+		int			numFinalArgs = peraggstate->numFinalArgs;
 		FunctionCallInfoData fcinfo;
+		bool		anynull;
+		int			i;
 
-		InitFunctionCallInfoData(fcinfo, &(peraggstate->finalfn), 1,
+		InitFunctionCallInfoData(fcinfo, &(peraggstate->finalfn),
+								 numFinalArgs,
 								 perfuncstate->winCollation,
 								 (void *) winstate, NULL);
 		fcinfo.arg[0] = peraggstate->transValue;
 		fcinfo.argnull[0] = peraggstate->transValueIsNull;
-		if (fcinfo.flinfo->fn_strict && peraggstate->transValueIsNull)
+		anynull = peraggstate->transValueIsNull;
+
+		/* Fill any remaining argument positions with nulls */
+		for (i = 1; i < numFinalArgs; i++)
+		{
+			fcinfo.arg[i] = (Datum) 0;
+			fcinfo.argnull[i] = true;
+			anynull = true;
+		}
+
+		if (fcinfo.flinfo->fn_strict && anynull)
 		{
 			/* don't call a strict function with NULL inputs */
 			*result = (Datum) 0;
@@ -2089,6 +2105,7 @@ initialize_peragg(WindowAggState *winstate, WindowFunc *wfunc,
 	Oid			transfn_oid,
 				invtransfn_oid,
 				finalfn_oid;
+	bool		finalextra;
 	Expr	   *transfnexpr,
 			   *invtransfnexpr,
 			   *finalfnexpr;
@@ -2127,6 +2144,7 @@ initialize_peragg(WindowAggState *winstate, WindowFunc *wfunc,
 		peraggstate->transfn_oid = transfn_oid = aggform->aggmtransfn;
 		peraggstate->invtransfn_oid = invtransfn_oid = aggform->aggminvtransfn;
 		peraggstate->finalfn_oid = finalfn_oid = aggform->aggmfinalfn;
+		finalextra = aggform->aggmfinalextra;
 		aggtranstype = aggform->aggmtranstype;
 		initvalAttNo = Anum_pg_aggregate_aggminitval;
 	}
@@ -2135,6 +2153,7 @@ initialize_peragg(WindowAggState *winstate, WindowFunc *wfunc,
 		peraggstate->transfn_oid = transfn_oid = aggform->aggtransfn;
 		peraggstate->invtransfn_oid = invtransfn_oid = InvalidOid;
 		peraggstate->finalfn_oid = finalfn_oid = aggform->aggfinalfn;
+		finalextra = aggform->aggfinalextra;
 		aggtranstype = aggform->aggtranstype;
 		initvalAttNo = Anum_pg_aggregate_agginitval;
 	}
@@ -2185,6 +2204,12 @@ initialize_peragg(WindowAggState *winstate, WindowFunc *wfunc,
 		}
 	}
 
+	/* Detect how many arguments to pass to the finalfn */
+	if (finalextra)
+		peraggstate->numFinalArgs = numArguments + 1;
+	else
+		peraggstate->numFinalArgs = 1;
+
 	/* resolve actual type of transition state, if polymorphic */
 	aggtranstype = resolve_aggregate_transtype(wfunc->winfnoid,
 											   aggtranstype,
@@ -2195,7 +2220,7 @@ initialize_peragg(WindowAggState *winstate, WindowFunc *wfunc,
 	build_aggregate_fnexprs(inputTypes,
 							numArguments,
 							0,	/* no ordered-set window functions yet */
-							false,
+							peraggstate->numFinalArgs,
 							false,		/* no variadic window functions yet */
 							aggtranstype,
 							wfunc->wintype,
@@ -2207,6 +2232,7 @@ initialize_peragg(WindowAggState *winstate, WindowFunc *wfunc,
 							&invtransfnexpr,
 							&finalfnexpr);
 
+	/* set up infrastructure for calling the transfn(s) and finalfn */
 	fmgr_info(transfn_oid, &peraggstate->transfn);
 	fmgr_info_set_expr((Node *) transfnexpr, &peraggstate->transfn);
 
@@ -2222,6 +2248,7 @@ initialize_peragg(WindowAggState *winstate, WindowFunc *wfunc,
 		fmgr_info_set_expr((Node *) finalfnexpr, &peraggstate->finalfn);
 	}
 
+	/* get info about relevant datatypes */
 	get_typlenbyval(wfunc->wintype,
 					&peraggstate->resulttypeLen,
 					&peraggstate->resulttypeByVal);