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

Author: michaelpq

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;
 }
 

src/backend/foreign/foreign.c

@@ -499,17 +499,19 @@ IsImportableForeignTable(const char *tablename,
 
 
 /*
- * deflist_to_tuplestore - Helper function to convert DefElem list to
- * tuplestore usable in SRF.
+ * pg_options_to_table - Convert options array to name/value table
+ *
+ * This is useful to provide details for information_schema and pg_dump.
  */
-static void
-deflist_to_tuplestore(ReturnSetInfo *rsinfo, List *options)
+Datum
+pg_options_to_table(PG_FUNCTION_ARGS)
 {
+	Datum		array = PG_GETARG_DATUM(0);
 	ListCell   *cell;
+	List	   *options;
+	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
 	TupleDesc	tupdesc;
 	Tuplestorestate *tupstore;
-	Datum		values[2];
-	bool		nulls[2];
 	MemoryContext per_query_ctx;
 	MemoryContext oldcontext;
 
@@ -524,6 +526,9 @@ deflist_to_tuplestore(ReturnSetInfo *rsinfo, List *options)
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("materialize mode required, but it is not allowed in this context")));
 
+	options = untransformRelOptions(array);
+	rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
+
 	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
 	oldcontext = MemoryContextSwitchTo(per_query_ctx);
 
@@ -536,9 +541,13 @@ deflist_to_tuplestore(ReturnSetInfo *rsinfo, List *options)
 	rsinfo->setResult = tupstore;
 	rsinfo->setDesc = tupdesc;
 
+	MemoryContextSwitchTo(oldcontext);
+
 	foreach(cell, options)
 	{
 		DefElem    *def = lfirst(cell);
+		Datum		values[2];
+		bool		nulls[2];
 
 		values[0] = CStringGetTextDatum(def->defname);
 		nulls[0] = false;
@@ -555,22 +564,6 @@ deflist_to_tuplestore(ReturnSetInfo *rsinfo, List *options)
 		tuplestore_putvalues(tupstore, tupdesc, values, nulls);
 	}
 
-	MemoryContextSwitchTo(oldcontext);
-}
-
-
-/*
- * Convert options array to name/value table.  Useful for information
- * schema and pg_dump.
- */
-Datum
-pg_options_to_table(PG_FUNCTION_ARGS)
-{
-	Datum		array = PG_GETARG_DATUM(0);
-
-	deflist_to_tuplestore((ReturnSetInfo *) fcinfo->resultinfo,
-						  untransformRelOptions(array));
-
 	return (Datum) 0;
 }
 

src/backend/utils/misc/guc.c

@@ -10174,30 +10174,16 @@ show_all_file_settings(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");
+
 	/* Scan the config files using current context as workspace */
 	conf = ProcessConfigFileInternal(PGC_SIGHUP, false, DEBUG3);
 
 	/* Switch into long-lived context to construct returned data structures */
 	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
 	oldcontext = MemoryContextSwitchTo(per_query_ctx);
 
-	/* Build a tuple descriptor for our result type */
-	tupdesc = CreateTemplateTupleDesc(NUM_PG_FILE_SETTINGS_ATTS);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 1, "sourcefile",
-					   TEXTOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 2, "sourceline",
-					   INT4OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 3, "seqno",
-					   INT4OID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 4, "name",
-					   TEXTOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 5, "setting",
-					   TEXTOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 6, "applied",
-					   BOOLOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 7, "error",
-					   TEXTOID, -1, 0);
-
 	/* Build a tuplestore to return our results in */
 	tupstore = tuplestore_begin_heap(true, false, work_mem);
 	rsinfo->returnMode = SFRM_Materialize;

src/backend/utils/misc/pg_config.c

@@ -26,80 +26,49 @@ pg_config(PG_FUNCTION_ARGS)
 {
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
 	Tuplestorestate *tupstore;
-	HeapTuple	tuple;
 	TupleDesc	tupdesc;
-	AttInMetadata *attinmeta;
-	MemoryContext per_query_ctx;
 	MemoryContext oldcontext;
 	ConfigData *configdata;
 	size_t		configdata_len;
-	char	   *values[2];
 	int			i = 0;
 
 	/* check to see if caller supports us returning a tuplestore */
 	if (rsinfo == NULL || !IsA(rsinfo, ReturnSetInfo))
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("set-valued function called in context that cannot accept a set")));
-	if (!(rsinfo->allowedModes & SFRM_Materialize) ||
-		rsinfo->expectedDesc == NULL)
+	if (!(rsinfo->allowedModes & SFRM_Materialize))
 		ereport(ERROR,
 				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 				 errmsg("materialize mode required, but it is not allowed in this context")));
 
-	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
-	oldcontext = MemoryContextSwitchTo(per_query_ctx);
+	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
 
-	/* get the requested return tuple description */
-	tupdesc = CreateTupleDescCopy(rsinfo->expectedDesc);
+	/* Build tuplestore to hold the result rows */
+	oldcontext = MemoryContextSwitchTo(rsinfo->econtext->ecxt_per_query_memory);
 
-	/*
-	 * Check to make sure we have a reasonable tuple descriptor
-	 */
-	if (tupdesc->natts != 2 ||
-		TupleDescAttr(tupdesc, 0)->atttypid != TEXTOID ||
-		TupleDescAttr(tupdesc, 1)->atttypid != TEXTOID)
-		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-				 errmsg("query-specified return tuple and "
-						"function return type are not compatible")));
-
-	/* OK to use it */
-	attinmeta = TupleDescGetAttInMetadata(tupdesc);
-
-	/* let the caller know we're sending back a tuplestore */
+	tupstore = tuplestore_begin_heap(true, false, work_mem);
 	rsinfo->returnMode = SFRM_Materialize;
+	rsinfo->setResult = tupstore;
+	rsinfo->setDesc = tupdesc;
 
-	/* initialize our tuplestore */
-	tupstore = tuplestore_begin_heap(true, false, work_mem);
+	MemoryContextSwitchTo(oldcontext);
 
 	configdata = get_configdata(my_exec_path, &configdata_len);
 	for (i = 0; i < configdata_len; i++)
 	{
-		values[0] = configdata[i].name;
-		values[1] = configdata[i].setting;
-
-		tuple = BuildTupleFromCStrings(attinmeta, values);
-		tuplestore_puttuple(tupstore, tuple);
-	}
+		Datum		values[2];
+		bool		nulls[2];
 
-	/*
-	 * no longer need the tuple descriptor reference created by
-	 * TupleDescGetAttInMetadata()
-	 */
-	ReleaseTupleDesc(tupdesc);
+		memset(values, 0, sizeof(values));
+		memset(nulls, 0, sizeof(nulls));
 
-	rsinfo->setResult = tupstore;
+		values[0] = CStringGetTextDatum(configdata[i].name);
+		values[1] = CStringGetTextDatum(configdata[i].setting);
 
-	/*
-	 * SFRM_Materialize mode expects us to return a NULL Datum. The actual
-	 * tuples are in our tuplestore and passed back through rsinfo->setResult.
-	 * rsinfo->setDesc is set to the tuple description that we actually used
-	 * to build our tuples with, so the caller can verify we did what it was
-	 * expecting.
-	 */
-	rsinfo->setDesc = tupdesc;
-	MemoryContextSwitchTo(oldcontext);
+		tuplestore_putvalues(tupstore, tupdesc, values, nulls);
+	}
 
 	return (Datum) 0;
 }

src/backend/utils/mmgr/portalmem.c

@@ -21,6 +21,7 @@
 #include "access/xact.h"
 #include "catalog/pg_type.h"
 #include "commands/portalcmds.h"
+#include "funcapi.h"
 #include "miscadmin.h"
 #include "storage/ipc.h"
 #include "utils/builtins.h"
@@ -1152,23 +1153,8 @@ pg_cursor(PG_FUNCTION_ARGS)
 	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_cursors view in system_views.sql
-	 */
-	tupdesc = CreateTemplateTupleDesc(6);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 1, "name",
-					   TEXTOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 2, "statement",
-					   TEXTOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 3, "is_holdable",
-					   BOOLOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 4, "is_binary",
-					   BOOLOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 5, "is_scrollable",
-					   BOOLOID, -1, 0);
-	TupleDescInitEntry(tupdesc, (AttrNumber) 6, "creation_time",
-					   TIMESTAMPTZOID, -1, 0);
+	if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
+		elog(ERROR, "return type must be a row type");
 
 	/*
 	 * We put all the tuples into a tuplestore in one scan of the hashtable.
@@ -1177,6 +1163,9 @@ pg_cursor(PG_FUNCTION_ARGS)
 	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);