Fix handling of polymorphic output arguments for procedures.

Most of the infrastructure for procedure arguments was already
okay with polymorphic output arguments, but it turns out that
CallStmtResultDesc() was a few bricks shy of a load here.  It thought
all it needed to do was call build_function_result_tupdesc_t, but
that function specifically disclaims responsibility for resolving
polymorphic arguments.  Failing to handle that doesn't seem to be
a problem for CALL in plpgsql, but CALL from plain SQL would get
errors like "cannot display a value of type anyelement", or even
crash outright.

In v14 and later we can simply examine the exposed types of the
CallStmt.outargs nodes to get the right type OIDs.  But it's a lot
more complicated to fix in v12/v13, because those versions don't
have CallStmt.outargs, nor do they do expand_function_arguments
until ExecuteCallStmt runs.  We have to duplicatively run
expand_function_arguments, and then re-determine which elements
of the args list are output arguments.

Per bug #18463 from Drew Kimball.  Back-patch to all supported
versions, since it's busted in all of them.

Discussion: https://postgr.es/m/18463-f8cd77e12564d8a2@postgresql.org

1 files changed, 28 insertions, 0 deletions

diff --git a/src/backend/commands/functioncmds.c b/src/backend/commands/functioncmds.c
index 9cf3fe8275e..6593fd7d811 100644
--- a/src/backend/commands/functioncmds.c
+++ b/src/backend/commands/functioncmds.c
@@ -52,6 +52,7 @@
 #include "executor/functions.h"
 #include "funcapi.h"
 #include "miscadmin.h"
+#include "nodes/nodeFuncs.h"
 #include "optimizer/optimizer.h"
 #include "parser/analyze.h"
 #include "parser/parse_coerce.h"
@@ -2364,5 +2365,32 @@ CallStmtResultDesc(CallStmt *stmt)
 
 	ReleaseSysCache(tuple);
 
+	/*
+	 * The result of build_function_result_tupdesc_t has the right column
+	 * names, but it just has the declared output argument types, which is the
+	 * wrong thing in polymorphic cases.  Get the correct types by examining
+	 * stmt->outargs.  We intentionally keep the atttypmod as -1 and the
+	 * attcollation as the type's default, since that's always the appropriate
+	 * thing for function outputs; there's no point in considering any
+	 * additional info available from outargs.  Note that tupdesc is null if
+	 * there are no outargs.
+	 */
+	if (tupdesc)
+	{
+		Assert(tupdesc->natts == list_length(stmt->outargs));
+		for (int i = 0; i < tupdesc->natts; i++)
+		{
+			Form_pg_attribute att = TupleDescAttr(tupdesc, i);
+			Node	   *outarg = (Node *) list_nth(stmt->outargs, i);
+
+			TupleDescInitEntry(tupdesc,
+							   i + 1,
+							   NameStr(att->attname),
+							   exprType(outarg),
+							   -1,
+							   0);
+		}
+	}
+
 	return tupdesc;
 }