noUnusedVariablesRule function

Visitor noUnusedVariablesRule(ValidationCtx context)

No unused variables

A GraphQL operation is only valid if all variables defined by an operation are used, either directly or within a spread fragment.

See https://spec.graphql.org/draft/#sec-All-Variables-Used

Implementation

Visitor noUnusedVariablesRule(ValidationCtx context) {
  final visitor = TypedVisitor();
  var variableDefs = <VariableDefinitionNode>[];

  visitor.add<VariableDefinitionNode>((def) {
    variableDefs.add(def);
  });
  visitor.add<OperationDefinitionNode>(
    (node) {
      variableDefs = [];
    },
    leave: (operation) {
      final variableNameUsed = <String, bool>{};
      final usages = context.getRecursiveVariableUsages(operation);

      for (final usage in usages) {
        variableNameUsed[usage.node.name.value] = true;
      }

      for (final variableDef in variableDefs) {
        final variableName = variableDef.variable.name.value;
        if (variableNameUsed[variableName] != true) {
          context.reportError(
            GraphQLError(
              operation.name != null
                  ? 'Variable "\$${variableName}" is never used in operation "${operation.name!.value}".'
                  : 'Variable "\$${variableName}" is never used.',
              locations: GraphQLErrorLocation.firstFromNodes(
                  [variableDef, variableDef.variable]),
              extensions: _noUnusedVariablesSpec.extensions(),
            ),
          );
        }
      }
    },
  );

  return visitor;
}