[PATCH v5 5/5] Improve tab completion for ALTER SYSTEM RESET for non-superusers

Non-superusers can only use ALTER SYSTEM on variables they've
explicitly been GRANTed access to, and can't read the data_directory
setting or pg_settings.sourceline column, so the existing tab
completion for ALTER SYSTEM isn't very useful for them.

Instead, query pg_parameter_acl to show the variables they do have
permission to set via ALTER SYSTEM.
---
 src/bin/psql/tab-complete.in.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index 60bba212f5e..aee939e98be 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -1049,6 +1049,13 @@ static const SchemaQuery Query_for_trigger_of_table = {
 "           '[_%%\\\\]', '\\\\\\&') || '_postgresql.auto.conf' " \
 "   AND pg_catalog.lower(name) LIKE pg_catalog.lower('%s')"
 
+#define Query_for_list_of_alter_system_granted_vars \
+"SELECT pg_catalog.lower(parname) FROM pg_catalog.pg_parameter_acl " \
+" WHERE EXISTS (SELECT FROM pg_catalog.aclexplode(paracl) " \
+"                WHERE pg_has_role(current_role, grantee, 'usage') " \
+"                  AND privilege_type = 'ALTER SYSTEM') " \
+"   AND pg_catalog.lower(parname) LIKE pg_catalog.lower('%s')"
+
 #define Query_for_list_of_set_vars \
 "SELECT pg_catalog.lower(name) FROM pg_catalog.pg_settings "\
 " WHERE context IN ('user', 'superuser') "\
@@ -2632,10 +2639,16 @@ match_previous_words(int pattern_id,
 	else if (Matches("ALTER", "SYSTEM"))
 		COMPLETE_WITH("SET", "RESET");
 	else if (Matches("ALTER", "SYSTEM", "SET"))
-		COMPLETE_WITH_QUERY_VERBATIM(Query_for_list_of_alter_system_set_vars);
+		if (is_superuser())
+			COMPLETE_WITH_QUERY_VERBATIM(Query_for_list_of_alter_system_set_vars);
+		else
+			COMPLETE_WITH_QUERY_VERBATIM(Query_for_list_of_alter_system_granted_vars);
 	else if (Matches("ALTER", "SYSTEM", "RESET"))
-		COMPLETE_WITH_QUERY_VERBATIM_PLUS(Query_for_list_of_alter_system_reset_vars,
-										  "ALL");
+		if (is_superuser())
+			COMPLETE_WITH_QUERY_VERBATIM_PLUS(Query_for_list_of_alter_system_reset_vars,
+											  "ALL");
+		else
+			COMPLETE_WITH_QUERY_VERBATIM(Query_for_list_of_alter_system_granted_vars);
 	else if (Matches("ALTER", "SYSTEM", "SET", MatchAny))
 		COMPLETE_WITH("TO");
 	/* ALTER VIEW <name> */
-- 
2.50.1


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