Module visit

Traversal of an immutable AST.

Each method of the Visit trait is a hook that can be overridden to customize the behavior when visiting the corresponding type of node. By default, every method recursively visits the substructure of the input by invoking the right visitor method of each of its fields.

pub trait Visit<'ast, T: AstInfo> {
    /* ... */

    fn visit_function(&mut self, node: &'ast Function<T>) {
        visit_function(self, node);
    }

    /* ... */
}

pub fn visit_function<'ast, V, T: AstInfo>(visitor: &mut V, node: &'ast Function<T>)
where
    V: Visit<'ast, T> + ?Sized,
{
    visitor.visit_item_name(&node.name);
    visitor.visit_function_args(&node.args);
    if let Some(filter) = &node.filter {
        visitor.visit_expr(&*filter);
    }
    if let Some(over) = &node.over {
        visitor.visit_window_spec(over);
    }
}

See also the visit_mut module for traversing mutable ASTs.

Examples

This visitor will count the number of subqueries in a SQL statement.

use std::error::Error;

use mz_sql_parser::ast::{AstInfo, Query, Raw};
use mz_sql_parser::ast::visit::{self, Visit};

struct SubqueryCounter {
    count: usize,
}

impl<'ast> Visit<'ast, Raw> for SubqueryCounter {
    fn visit_query(&mut self, query: &'ast Query<Raw>) {
        self.count += 1;

        // Delegate to the default implementation to visit any nested
        // subqueries. Placing this call at the end of the method results
        // in a pre-order traversal. Place it at the beginning for a
        // post-order traversal instead.
        visit::visit_query(self, query);
    }
}

fn main() -> Result<(), Box<dyn Error>> {
    let sql = "SELECT (SELECT 1) FROM (SELECT 1) WHERE EXISTS (SELECT (SELECT 1))";
    let stmts = mz_sql_parser::parser::parse_statements(sql.into())?;

    let mut counter = SubqueryCounter { count: 0 };
    for stmt in &stmts {
        counter.visit_statement(&stmt.ast);
    }
    assert_eq!(counter.count, 5);
    Ok(())
}

The 'ast lifetime on the input references means that the syntax tree outlives the complete recursive visit call, so the visitor is allowed to hold on to references into the syntax tree.

use std::error::Error;

use mz_sql_parser::ast::{Ident, Raw, AstInfo, RawItemName};
use mz_sql_parser::ast::visit::{self, Visit};

struct IdentCollector<'ast> {
    idents: Vec<&'ast Ident>,
}

impl<'ast> Visit<'ast, Raw> for IdentCollector<'ast> {
    fn visit_ident(&mut self, node: &'ast Ident) {
        self.idents.push(node);
        visit::visit_ident(self, node);
    }
    fn visit_item_name(&mut self, name: &'ast <Raw as AstInfo>::ItemName) {
        match name {
            RawItemName::Name(n) | RawItemName::Id(_, n, _) => {
                for node in &n.0 {
                    self.idents.push(node);
                    visit::visit_ident(self, node);
                }
            }
        }
    }
}

fn main() -> Result<(), Box<dyn Error>> {
    let sql = "SELECT a FROM b.c WHERE 1 + d(e)";
    let stmts = mz_sql_parser::parser::parse_statements(sql.into())?;

    let mut collector = IdentCollector { idents: vec![] };
    for stmt in &stmts {
        collector.visit_statement(&stmt.ast);
    }
    assert_eq!(collector.idents, &[
        &Ident::new_unchecked("a"), &Ident::new_unchecked("b"),
        &Ident::new_unchecked("c"), &Ident::new_unchecked("d"),
        &Ident::new_unchecked("e"),
    ]);
    Ok(())
}

The VisitNode trait is implemented for every node in the AST and can be used to write generic functions that apply a Visit implementation to any node in the AST.

Implementation notes

This module is automatically generated by the crate’s build script. Changes to the AST will be automatically propagated to the visitor.

This approach to AST visitors is inspired by the syn crate. These module docs are directly derived from the syn::visit module docs.

Traits

Visit

VisitNode

Functions

visit_abbreviated_grant_or_revoke_statement

visit_abbreviated_grant_statement

visit_abbreviated_revoke_statement

visit_alter_cluster_action

visit_alter_cluster_statement

visit_alter_connection_action

visit_alter_connection_option

visit_alter_connection_option_name

visit_alter_connection_statement

visit_alter_default_privileges_statement

visit_alter_index_action

visit_alter_index_statement

visit_alter_network_policy_statement

visit_alter_object_rename_statement

visit_alter_object_swap_statement

visit_alter_owner_statement

visit_alter_retain_history_statement

visit_alter_role_option

visit_alter_role_statement

visit_alter_secret_statement

visit_alter_set_cluster_statement

visit_alter_sink_action

visit_alter_sink_statement

visit_alter_source_action

visit_alter_source_add_subsource_option

visit_alter_source_add_subsource_option_name

visit_alter_source_statement

visit_alter_system_reset_all_statement

visit_alter_system_reset_statement

visit_alter_system_set_statement

visit_alter_table_add_column_statement

visit_as_of

visit_assignment

visit_avro_doc_on

visit_avro_schema

visit_avro_schema_option

visit_avro_schema_option_name

visit_catalog_name

visit_close_statement

visit_cluster_alter_option

visit_cluster_alter_option_name

visit_cluster_alter_option_value

visit_cluster_alter_until_ready_option

visit_cluster_alter_until_ready_option_name

visit_cluster_feature

visit_cluster_feature_name

visit_cluster_name

visit_cluster_option

visit_cluster_option_name

visit_cluster_schedule_option_value

visit_column_def

visit_column_name

visit_column_option

visit_column_option_def

visit_column_reference

visit_column_versioned

visit_comment_object_type

visit_comment_statement

visit_commit_statement

visit_connection_default_aws_privatelink

visit_connection_option

visit_connection_option_name

visit_continual_task_option

visit_continual_task_option_name

visit_continual_task_stmt

visit_copy_direction

visit_copy_option

visit_copy_option_name

visit_copy_relation

visit_copy_statement

visit_copy_target

visit_create_cluster_replica_statement

visit_create_cluster_statement

visit_create_connection_option

visit_create_connection_option_name

visit_create_connection_statement

visit_create_connection_type

visit_create_continual_task_statement

visit_create_continual_task_sugar

visit_create_database_statement

visit_create_index_statement

visit_create_materialized_view_statement

visit_create_network_policy_statement

visit_create_role_statement

visit_create_schema_statement

visit_create_secret_statement

visit_create_sink_connection

visit_create_sink_option

visit_create_sink_option_name

visit_create_sink_statement

visit_create_source_connection

visit_create_source_option

visit_create_source_option_name

visit_create_source_statement

visit_create_subsource_option

visit_create_subsource_option_name

visit_create_subsource_statement

visit_create_table_from_source_statement

visit_create_table_statement

visit_create_type_as

visit_create_type_list_option

visit_create_type_list_option_name

visit_create_type_map_option

visit_create_type_map_option_name

visit_create_type_statement

visit_create_view_statement

visit_create_webhook_source_body

visit_create_webhook_source_check

visit_create_webhook_source_check_options

visit_create_webhook_source_filter_header

visit_create_webhook_source_header

visit_create_webhook_source_include_headers

visit_create_webhook_source_map_header

visit_create_webhook_source_secret

visit_create_webhook_source_statement

visit_csr_config_option

visit_csr_config_option_name

visit_csr_connection

visit_csr_connection_avro

visit_csr_connection_protobuf

visit_csr_seed_avro

visit_csr_seed_protobuf

visit_csr_seed_protobuf_schema

visit_csv_columns

visit_cte

visit_cte_block

visit_cte_id

visit_cte_mut_rec

visit_cte_mut_rec_column_def

visit_data_type

visit_database_name

visit_date_time_field

visit_deallocate_statement

visit_declare_statement

visit_deferred_item_name

visit_delete_statement

visit_discard_statement

visit_discard_target

visit_distinct

visit_doc_on_identifier

visit_doc_on_schema

visit_drop_objects_statement

visit_drop_owned_statement

visit_execute_statement

visit_explain_analyze_computation_property

visit_explain_analyze_property

visit_explain_analyze_statement

visit_explain_format

visit_explain_plan_option

visit_explain_plan_option_name

visit_explain_plan_statement

visit_explain_pushdown_statement

visit_explain_sink_schema_for

visit_explain_sink_schema_statement

visit_explain_stage

visit_explain_timestamp_statement

visit_explainee

visit_expr

visit_external_reference_export

visit_external_references

visit_fetch_direction

visit_fetch_option

visit_fetch_option_name

visit_fetch_statement

visit_format

visit_format_specifier

visit_function

visit_function_args

visit_grant_privileges_statement

visit_grant_role_statement

visit_grant_target_all_specification

visit_grant_target_specification

visit_grant_target_specification_inner

visit_homogenizing_function

visit_ident

visit_ident_error

visit_if_exists_behavior

visit_index_option

visit_index_option_name

visit_insert_source

visit_insert_statement

visit_inspect_shard_statement

visit_interval_value

visit_is_expr_construct

visit_item_name

visit_join

visit_join_constraint

visit_join_operator

visit_kafka_broker

visit_kafka_broker_aws_privatelink

visit_kafka_broker_aws_privatelink_option

visit_kafka_broker_aws_privatelink_option_name

visit_kafka_broker_tunnel

visit_kafka_sink_config_option

visit_kafka_sink_config_option_name

visit_kafka_sink_key

visit_kafka_source_config_option

visit_kafka_source_config_option_name

visit_key_constraint

visit_limit

visit_load_generator

visit_load_generator_option

visit_load_generator_option_name

visit_map_entry

visit_materialized_view_option

visit_materialized_view_option_name

visit_mut_rec_block

visit_mut_rec_block_option

visit_mut_rec_block_option_name

visit_my_sql_config_option

visit_my_sql_config_option_name

visit_named_plan

visit_nested_statement

visit_network_policy_name

visit_network_policy_option

visit_network_policy_option_name

visit_network_policy_rule_definition

visit_network_policy_rule_option

visit_network_policy_rule_option_name

visit_notice_severity

visit_object_name

visit_object_type

visit_op

visit_order_by_expr

visit_pg_config_option

visit_pg_config_option_name

visit_prepare_statement

visit_privilege

visit_privilege_specification

visit_protobuf_schema

visit_qualified_replica

visit_query

visit_raise_statement

visit_reader_schema_selection_strategy

visit_reassign_owned_statement

visit_refresh_at_option_value

visit_refresh_every_option_value

visit_refresh_option_value

visit_replica_definition

visit_replica_option

visit_replica_option_name

visit_reset_variable_statement

visit_revoke_privileges_statement

visit_revoke_role_statement

visit_role_attribute

visit_role_name

visit_rollback_statement

visit_schema

visit_schema_name

visit_select

visit_select_item

visit_select_option

visit_select_option_name

visit_select_statement

visit_set_expr

visit_set_operator

visit_set_role_var

visit_set_transaction_statement

visit_set_variable_statement

visit_set_variable_to

visit_set_variable_value

visit_show_columns_statement

visit_show_create_cluster_statement

visit_show_create_connection_statement

visit_show_create_index_statement

visit_show_create_materialized_view_statement

visit_show_create_sink_statement

visit_show_create_source_statement

visit_show_create_table_statement

visit_show_create_view_statement

visit_show_object_type

visit_show_objects_statement

visit_show_statement

visit_show_statement_filter

visit_show_variable_statement

visit_sink_envelope

visit_source_envelope

visit_source_error_policy

visit_source_include_metadata

visit_sql_server_config_option

visit_sql_server_config_option_name

visit_start_transaction_statement

visit_statement

visit_subscribe_option

visit_subscribe_option_name

visit_subscribe_output

visit_subscribe_relation

visit_subscribe_statement

visit_subscript_position

visit_system_object_type

visit_table_alias

visit_table_constraint

visit_table_factor

visit_table_from_source_columns

visit_table_from_source_option

visit_table_from_source_option_name

visit_table_option

visit_table_option_name

visit_table_with_joins

visit_target_role_specification

visit_transaction_access_mode

visit_transaction_isolation_level

visit_transaction_mode

visit_unresolved_database_name

visit_unresolved_item_name

visit_unresolved_object_name

visit_unresolved_schema_name

visit_update_statement

visit_validate_connection_statement

visit_value

visit_value_error

visit_values

visit_version

visit_view_definition

visit_window_frame

visit_window_frame_bound

visit_window_frame_units

visit_window_spec

visit_with_option_value