Every current metric must have documentation

src/Core/Settings.h

@@ -506,7 +506,7 @@ static constexpr UInt64 operator""_GiB(unsigned long long value)
     M(Bool, alter_partition_verbose_result, false, "Output information about affected parts. Currently works only for FREEZE and ATTACH commands.", 0) \
     M(Bool, allow_experimental_database_materialized_mysql, false, "Allow to create database with Engine=MaterializedMySQL(...).", 0) \
     M(Bool, allow_experimental_database_materialized_postgresql, false, "Allow to create database with Engine=MaterializedPostgreSQL(...).", 0) \
-    M(Bool, system_events_show_zero_values, false, "Include all metrics, even with zero values", 0) \
+    M(Bool, system_events_show_zero_values, false, "When querying system.events or system.metrics tables, include all metrics, even with zero values.", 0) \
     M(MySQLDataTypesSupport, mysql_datatypes_support_level, 0, "Which MySQL types should be converted to corresponding ClickHouse types (rather than being represented as String). Can be empty or any combination of 'decimal', 'datetime64', 'date2Date32' or 'date2String'. When empty MySQL's DECIMAL and DATETIME/TIMESTAMP with non-zero precision are seen as String on ClickHouse's side.", 0) \
     M(Bool, optimize_trivial_insert_select, true, "Optimize trivial 'INSERT INTO table SELECT ... FROM TABLES' query", 0) \
     M(Bool, allow_non_metadata_alters, true, "Allow to execute alters which affects not only tables metadata, but also data on disk", 0) \

tests/queries/0_stateless/02393_every_metric_must_have_documentation.sql

@@ -0,0 +1,2 @@
+SET system_events_show_zero_values = true;
+SELECT metric FROM system.metrics WHERE length(description) < 10;