Clean up and simplify code in a couple of set-returning functions

The following set-returning functions have their logic simplified, to be
more consistent with other in-core areas:
- pg_prepared_statement()'s tuple descriptor is now created with
get_call_result_type() instead of being created from scratch, saving
from some duplication with pg_proc.dat.
- show_all_file_settings(), similarly, now uses get_call_result_type()
to build its tuple descriptor instead of creating it from scratch.
- pg_options_to_table() made use of a static routine called only once.
This commit removes this internal routine to make the function easier to
follow.
- pg_config() was using a unique logic style, doing checks on the tuple
descriptor passed down in expectedDesc, but it has no need to do so.
This switches the function to use a tuplestore with a tuple descriptor
retrieved from get_call_result_type(), instead.

This simplifies an upcoming patch aimed at refactoring the way
tuplestores are created and checked in set-returning functions, this
change making sense as its own independent cleanup by shaving some
code.

Author: Melanie Plageman, Michael Paquier
Reviewed-by: Justin Pryzby
Discussion: https://postgr.es/m/CAAKRu_azyd1Z3W_r7Ou4sorTjRCs+PxeHw1CWJeXKofkE6TuZg@mail.gmail.com

1 files changed, 7 insertions, 24 deletions

diff --git a/src/backend/commands/prepare.c b/src/backend/commands/prepare.c
index e0c985ef8b0..dce30aed6c1 100644
--- a/src/backend/commands/prepare.c
+++ b/src/backend/commands/prepare.c
@@ -22,6 +22,7 @@
 #include "catalog/pg_type.h"
 #include "commands/createas.h"
 #include "commands/prepare.h"
+#include "funcapi.h"
 #include "miscadmin.h"
 #include "nodes/nodeFuncs.h"
 #include "parser/analyze.h"
@@ -716,37 +717,23 @@ pg_prepared_statement(PG_FUNCTION_ARGS)
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("materialize mode required, but it is not allowed in this context")));
 
+	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
+
 	/* need to build tuplestore in query context */
 	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
 	oldcontext = MemoryContextSwitchTo(per_query_ctx);
 
 	/*
-	 * build tupdesc for result tuples. This must match the definition of the
-	 * pg_prepared_statements view in system_views.sql
-	 */
-	tupdesc = CreateTemplateTupleDesc(7);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 1, "name",
-					   TEXTOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 2, "statement",
-					   TEXTOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 3, "prepare_time",
-					   TIMESTAMPTZOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 4, "parameter_types",
-					   REGTYPEARRAYOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 5, "from_sql",
-					   BOOLOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 6, "generic_plans",
-					   INT8OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 7, "custom_plans",
-					   INT8OID, -1, 0);
-
-	/*
 	 * We put all the tuples into a tuplestore in one scan of the hashtable.
 	 * This avoids any issue of the hashtable possibly changing between calls.
 	 */
 	tupstore =
 		tuplestore_begin_heap(rsinfo->allowedModes & SFRM_Materialize_Random,
 							  false, work_mem);
+	rsinfo->returnMode = SFRM_Materialize;
+	rsinfo->setResult = tupstore;
+	rsinfo->setDesc = tupdesc;
 
 	/* generate junk in short-term context */
 	MemoryContextSwitchTo(oldcontext);
@@ -778,10 +765,6 @@ pg_prepared_statement(PG_FUNCTION_ARGS)
 		}
 	}
 
-	rsinfo->returnMode = SFRM_Materialize;
-	rsinfo->setResult = tupstore;
-	rsinfo->setDesc = tupdesc;
-
 	return (Datum) 0;
 }