cql3: expr: Add is_empty_restriction

Add a function to check whether
an expression restricts anything at all.

Signed-off-by: Jan Ciolek <jan.ciolek@scylladb.com>

cql3/expr/expression.cc

@@ -2407,5 +2407,14 @@ single_column_restrictions_map get_single_column_restrictions_map(const expressi
 
     return result;
 }
+
+bool is_empty_restriction(const expression& e) {
+    bool contains_non_conjunction = recurse_until(e, [&](const expression& e) -> bool {
+        return !is<conjunction>(e);
+    });
+
+    return !contains_non_conjunction;
+}
+
 } // namespace expr
 } // namespace cql3

cql3/expr/expression.hh

@@ -759,6 +759,9 @@ using single_column_restrictions_map = std::map<const column_definition*, expres
 // Extracts map of single column restrictions for each column from expression
 single_column_restrictions_map get_single_column_restrictions_map(const expression&);
 
+// Checks whether this expression is empty - doesn't restrict anything
+bool is_empty_restriction(const expression&);
+
 } // namespace expr
 
 } // namespace cql3