Simplify SRFs using materialize mode in contrib/ modules

9e98583 introduced a helper to centralize building their needed state
(tuplestore, tuple descriptors, etc.), checking for any errors.  This
commit updates all places of contrib/ that can be switched to use
SetSingleFuncCall() as a drop-in replacement, resulting in the removal
of a lot of boilerplate code in all the modules updated by this commit.

Per analysis, some places remain as they are:
- pg_logdir_ls() in adminpack/ uses historically TYPEFUNC_RECORD as
return type, and I suspect that changing it may cause issues at run-time
with some of its past versions, down to 1.0.
- dblink/ uses a wrapper function doing exactly the work of
SetSingleFuncCall().  Here the switch should be possible, but rather
invasive so it does not seem the extra backpatch maintenance cost.
- tablefunc/, similarly, uses multiple helper functions with portions of
SetSingleFuncCall() spread across the code paths of this module.

Author: Melanie Plageman
Discussion: https://postgr.es/m/CAAKRu_bvDPJoL9mH6eYwvBpPtTGQwbDzfJbCM-OjkSZDu5yTPg@mail.gmail.com

1 files changed, 10 insertions, 62 deletions

diff --git a/contrib/xml2/xpath.c b/contrib/xml2/xpath.c
index a2e5fb54e20..b8ee757674d 100644
--- a/contrib/xml2/xpath.c
+++ b/contrib/xml2/xpath.c
@@ -491,15 +491,9 @@ xpath_table(PG_FUNCTION_ARGS)
 	HeapTuple	spi_tuple;
 	TupleDesc	spi_tupdesc;
 
-	/* Output tuple (tuplestore) support */
-	Tuplestorestate *tupstore = NULL;
-	TupleDesc	ret_tupdesc;
-	HeapTuple	ret_tuple;
 
 	ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
 	AttInMetadata *attinmeta;
-	MemoryContext per_query_ctx;
-	MemoryContext oldcontext;
 
 	char	  **values;
 	xmlChar   **xpaths;
@@ -517,48 +511,10 @@ xpath_table(PG_FUNCTION_ARGS)
 	PgXmlErrorContext *xmlerrcxt;
 	volatile xmlDocPtr doctree = NULL;
 
-	/* We only have a valid tuple description in table function mode */
-	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->expectedDesc == NULL)
-		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-				 errmsg("xpath_table must be called as a table function")));
-
-	/*
-	 * We want to materialise because it means that we don't have to carry
-	 * libxml2 parser state between invocations of this function
-	 */
-	if (!(rsinfo->allowedModes & SFRM_Materialize))
-		ereport(ERROR,
-				(errcode(ERRCODE_SYNTAX_ERROR),
-				 errmsg("xpath_table requires Materialize mode, but it is not "
-						"allowed in this context")));
-
-	/*
-	 * The tuplestore must exist in a higher context than this function call
-	 * (per_query_ctx is used)
-	 */
-	per_query_ctx = rsinfo->econtext->ecxt_per_query_memory;
-	oldcontext = MemoryContextSwitchTo(per_query_ctx);
-
-	/*
-	 * Create the tuplestore - work_mem is the max in-memory size before a
-	 * file is created on disk to hold it.
-	 */
-	tupstore =
-		tuplestore_begin_heap(rsinfo->allowedModes & SFRM_Materialize_Random,
-							  false, work_mem);
-
-	MemoryContextSwitchTo(oldcontext);
-
-	/* get the requested return tuple description */
-	ret_tupdesc = CreateTupleDescCopy(rsinfo->expectedDesc);
+	SetSingleFuncCall(fcinfo, SRF_SINGLE_USE_EXPECTED);
 
 	/* must have at least one output column (for the pkey) */
-	if (ret_tupdesc->natts < 1)
+	if (rsinfo->setDesc->natts < 1)
 		ereport(ERROR,
 				(errcode(ERRCODE_SYNTAX_ERROR),
 				 errmsg("xpath_table must have at least one output column")));
@@ -571,14 +527,10 @@ xpath_table(PG_FUNCTION_ARGS)
 	 * representation.
 	 */
 
-	attinmeta = TupleDescGetAttInMetadata(ret_tupdesc);
-
-	/* Set return mode and allocate value space. */
-	rsinfo->returnMode = SFRM_Materialize;
-	rsinfo->setDesc = ret_tupdesc;
+	attinmeta = TupleDescGetAttInMetadata(rsinfo->setDesc);
 
-	values = (char **) palloc(ret_tupdesc->natts * sizeof(char *));
-	xpaths = (xmlChar **) palloc(ret_tupdesc->natts * sizeof(xmlChar *));
+	values = (char **) palloc(rsinfo->setDesc->natts * sizeof(char *));
+	xpaths = (xmlChar **) palloc(rsinfo->setDesc->natts * sizeof(xmlChar *));
 
 	/*
 	 * Split XPaths. xpathset is a writable CString.
@@ -587,7 +539,7 @@ xpath_table(PG_FUNCTION_ARGS)
 	 */
 	numpaths = 0;
 	pos = xpathset;
-	while (numpaths < (ret_tupdesc->natts - 1))
+	while (numpaths < (rsinfo->setDesc->natts - 1))
 	{
 		xpaths[numpaths++] = (xmlChar *) pos;
 		pos = strstr(pos, pathsep);
@@ -621,9 +573,6 @@ xpath_table(PG_FUNCTION_ARGS)
 	tuptable = SPI_tuptable;
 	spi_tupdesc = tuptable->tupdesc;
 
-	/* Switch out of SPI context */
-	MemoryContextSwitchTo(oldcontext);
-
 	/*
 	 * Check that SPI returned correct result. If you put a comma into one of
 	 * the function parameters, this will catch it when the SPI query returns
@@ -655,6 +604,7 @@ xpath_table(PG_FUNCTION_ARGS)
 			xmlXPathObjectPtr res;
 			xmlChar    *resstr;
 			xmlXPathCompExprPtr comppath;
+			HeapTuple	ret_tuple;
 
 			/* Extract the row data as C Strings */
 			spi_tuple = tuptable->vals[i];
@@ -666,7 +616,7 @@ xpath_table(PG_FUNCTION_ARGS)
 			 * return NULL in all columns.  Note that this also means that
 			 * spare columns will be NULL.
 			 */
-			for (j = 0; j < ret_tupdesc->natts; j++)
+			for (j = 0; j < rsinfo->setDesc->natts; j++)
 				values[j] = NULL;
 
 			/* Insert primary key */
@@ -682,7 +632,7 @@ xpath_table(PG_FUNCTION_ARGS)
 			{
 				/* not well-formed, so output all-NULL tuple */
 				ret_tuple = BuildTupleFromCStrings(attinmeta, values);
-				tuplestore_puttuple(tupstore, ret_tuple);
+				tuplestore_puttuple(rsinfo->setResult, ret_tuple);
 				heap_freetuple(ret_tuple);
 			}
 			else
@@ -749,7 +699,7 @@ xpath_table(PG_FUNCTION_ARGS)
 					if (had_values)
 					{
 						ret_tuple = BuildTupleFromCStrings(attinmeta, values);
-						tuplestore_puttuple(tupstore, ret_tuple);
+						tuplestore_puttuple(rsinfo->setResult, ret_tuple);
 						heap_freetuple(ret_tuple);
 					}
 
@@ -785,8 +735,6 @@ xpath_table(PG_FUNCTION_ARGS)
 
 	SPI_finish();
 
-	rsinfo->setResult = tupstore;
-
 	/*
 	 * SFRM_Materialize mode expects us to return a NULL Datum. The actual
 	 * tuples are in our tuplestore and passed back through rsinfo->setResult.