Complete tab completion for DROP STATISTICS

Tab-completing DROP STATISTICS would only work if you started writing
the schema name containing the statistics object, because the visibility
clause was missing.  To add it, we need to add SQL-callable support for
testing visibility of a statistics object, like all other object types
already have.

Discussion: https://postgr.es/m/22676.1494557205@sss.pgh.pa.us

2 files changed, 79 insertions, 0 deletions

diff --git a/src/backend/catalog/namespace.c b/src/backend/catalog/namespace.c
index e521bd908a..5b339222af 100644
--- a/src/backend/catalog/namespace.c
+++ b/src/backend/catalog/namespace.c
@@ -34,6 +34,7 @@
 #include "catalog/pg_operator.h"
 #include "catalog/pg_opfamily.h"
 #include "catalog/pg_proc.h"
+#include "catalog/pg_statistic_ext.h"
 #include "catalog/pg_ts_config.h"
 #include "catalog/pg_ts_dict.h"
 #include "catalog/pg_ts_parser.h"
@@ -2142,6 +2143,72 @@ get_statistics_oid(List *names, bool missing_ok)
 }
 
 /*
+ * StatisticsObjIsVisible
+ *		Determine whether a statistics object (identified by OID) is visible in
+ *		the current search path.  Visible means "would be found by searching
+ *		for the unqualified statistics object name".
+ */
+bool
+StatisticsObjIsVisible(Oid relid)
+{
+	HeapTuple	stxtup;
+	Form_pg_statistic_ext stxform;
+	Oid			stxnamespace;
+	bool		visible;
+
+	stxtup = SearchSysCache1(STATEXTOID, ObjectIdGetDatum(relid));
+	if (!HeapTupleIsValid(stxtup))
+		elog(ERROR, "cache lookup failed for statistics object %u", relid);
+	stxform = (Form_pg_statistic_ext) GETSTRUCT(stxtup);
+
+	recomputeNamespacePath();
+
+	/*
+	 * Quick check: if it ain't in the path at all, it ain't visible. Items in
+	 * the system namespace are surely in the path and so we needn't even do
+	 * list_member_oid() for them.
+	 */
+	stxnamespace = stxform->stxnamespace;
+	if (stxnamespace != PG_CATALOG_NAMESPACE &&
+		!list_member_oid(activeSearchPath, stxnamespace))
+		visible = false;
+	else
+	{
+		/*
+		 * If it is in the path, it might still not be visible; it could be
+		 * hidden by another statistics object of the same name earlier in the
+		 * path. So we must do a slow check for conflicting objects.
+		 */
+		char	   *stxname = NameStr(stxform->stxname);
+		ListCell   *l;
+
+		visible = false;
+		foreach(l, activeSearchPath)
+		{
+			Oid			namespaceId = lfirst_oid(l);
+
+			if (namespaceId == stxnamespace)
+			{
+				/* Found it first in path */
+				visible = true;
+				break;
+			}
+			if (SearchSysCacheExists2(STATEXTNAMENSP,
+									  PointerGetDatum(stxname),
+									  ObjectIdGetDatum(namespaceId)))
+			{
+				/* Found something else first in path */
+				break;
+			}
+		}
+	}
+
+	ReleaseSysCache(stxtup);
+
+	return visible;
+}
+
+/*
  * get_ts_parser_oid - find a TS parser by possibly qualified name
  *
  * If not found, returns InvalidOid if missing_ok, else throws error
@@ -4236,6 +4303,17 @@ pg_conversion_is_visible(PG_FUNCTION_ARGS)
 }
 
 Datum
+pg_statistic_ext_is_visible(PG_FUNCTION_ARGS)
+{
+	Oid			oid = PG_GETARG_OID(0);
+
+	if (!SearchSysCacheExists1(STATEXTOID, ObjectIdGetDatum(oid)))
+		PG_RETURN_NULL();
+
+	PG_RETURN_BOOL(StatisticsObjIsVisible(oid));
+}
+
+Datum
 pg_ts_parser_is_visible(PG_FUNCTION_ARGS)
 {
 	Oid			oid = PG_GETARG_OID(0);
diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c
index 236d876b1c..720e540276 100644
--- a/src/backend/utils/cache/lsyscache.c
+++ b/src/backend/utils/cache/lsyscache.c
@@ -32,6 +32,7 @@
 #include "catalog/pg_proc.h"
 #include "catalog/pg_range.h"
 #include "catalog/pg_statistic.h"
+#include "catalog/pg_statistic_ext.h"
 #include "catalog/pg_transform.h"
 #include "catalog/pg_type.h"
 #include "miscadmin.h"