traverse

@pgsql/traverse

PostgreSQL AST traversal utilities for pgsql-parser. This package provides a visitor pattern for traversing PostgreSQL Abstract Syntax Tree (AST) nodes, similar to Babel's traverse functionality but specifically designed for PostgreSQL AST structures.

Installation

npm install @pgsql/traverse

Usage

Walk API (Recommended)

The walk function provides improved traversal with NodePath context and early return support:

import { walk, NodePath } from '@pgsql/traverse';
import type { Walker, Visitor } from '@pgsql/traverse';

// Using a simple walker function
const walker: Walker = (path: NodePath) => {
  console.log(`Visiting ${path.tag} at path:`, path.path);
  
  // Return false to skip traversing children
  if (path.tag === 'SelectStmt') {
    return false; // Skip SELECT statement children
  }
};

walk(ast, walker);

// Using a visitor object (recommended for multiple node types)
const visitor: Visitor = {
  SelectStmt: (path) => {
    console.log('SELECT statement:', path.node);
  },
  RangeVar: (path) => {
    console.log('Table:', path.node.relname);
    console.log('Path to table:', path.path);
    console.log('Parent node:', path.parent?.tag);
  }
};

walk(ast, visitor);

NodePath Class

The NodePath class provides rich context information:

class NodePath<TTag extends NodeTag = NodeTag> {
  tag: TTag;           // Node type (e.g., 'SelectStmt', 'RangeVar')
  node: Node[TTag];    // The actual node data
  parent: NodePath | null;  // Parent NodePath (null for root)
  keyPath: readonly (string | number)[];  // Full path array
  
  get path(): (string | number)[];  // Copy of keyPath
  get key(): string | number;       // Last element of path
}

Runtime Schema Integration

The new implementation uses PostgreSQL's runtime schema to precisely determine which fields contain Node types that need traversal, eliminating guesswork and improving accuracy.

Visit API

The original visit function is still available for backward compatibility:

import { visit } from '@pgsql/traverse';

const visitor = {
  SelectStmt: (node, ctx) => {
    console.log('Found SELECT statement:', node);
    console.log('Path:', ctx.path);
  },
  RangeVar: (node, ctx) => {
    console.log('Found table reference:', node.relname);
  }
};

// Parse some SQL and traverse the AST
const ast = /* your parsed AST */;
visit(ast, visitor);

Working with ParseResult

import { walk } from '@pgsql/traverse';

const visitor = {
  ParseResult: (path) => {
    console.log('Parse result version:', path.node.version);
    console.log('Number of statements:', path.node.stmts.length);
  },
  SelectStmt: (path) => {
    console.log('SELECT statement found');
  }
};

walk(parseResult, visitor);

Using Visitor Context

The visitor context provides information about the current traversal state:

const visitor = {
  RangeVar: (path) => {
    console.log('Table name:', path.node.relname);
    console.log('Path to this node:', path.path);
    console.log('Parent node:', path.parent?.tag);
    console.log('Key in parent:', path.key);
  }
};

Collecting Information During Traversal

import { visit } from '@pgsql/traverse';
import type { Visitor } from '@pgsql/traverse';

const tableNames: string[] = [];
const columnRefs: string[] = [];

const visitor: Visitor = {
  RangeVar: (node) => {
    if (node.relname) {
      tableNames.push(node.relname);
    }
  },
  ColumnRef: (node) => {
    if (node.fields) {
      node.fields.forEach(field => {
        if (field.String?.sval) {
          columnRefs.push(field.String.sval);
        }
      });
    }
  }
};

visit(ast, visitor);

console.log('Tables referenced:', tableNames);
console.log('Columns referenced:', columnRefs);

API

walk(root, callback, parent?, keyPath?)

Walks the tree of PostgreSQL AST nodes using runtime schema for precise traversal.

Parameters:

• root: The AST node to traverse
• callback: A walker function or visitor object
• parent?: Optional parent NodePath (for internal use)
• keyPath?: Optional key path array (for internal use)

Example:

walk(ast, {
  SelectStmt: (path) => {
    // Handle SELECT statements
    // Return false to skip children
  },
  RangeVar: (path) => {
    // Handle table references
  }
});

visit(node, visitor, ctx?) (Legacy)

Recursively visits a PostgreSQL AST node, calling any matching visitor functions. Maintained for backward compatibility.

Parameters:

• node: The AST node to traverse
• visitor: An object with visitor functions for different node types
• ctx?: Optional initial visitor context

Types

Visitor

An object type where keys are node type names and values are walker functions:

type Visitor = {
  [TTag in NodeTag]?: Walker<NodePath<TTag>>;
};

Walker

A function that receives a NodePath and can return false to skip children:

type Walker<TNodePath extends NodePath = NodePath> = (
  path: TNodePath,
) => boolean | void;

NodePath

A class that encapsulates node traversal context:

class NodePath<TTag extends NodeTag = NodeTag> {
  tag: TTag;                                    // Node type
  node: Node[TTag];                            // Node data
  parent: NodePath | null;                     // Parent path
  keyPath: readonly (string | number)[];       // Full path
  
  get path(): (string | number)[];             // Path copy
  get key(): string | number;                  // Current key
}

VisitorContext (Legacy)

Context information provided to legacy visitor functions:

type VisitorContext = {
  path: (string | number)[];  // Path to current node
  parent: any;                // Parent node
  key: string | number;       // Key in parent node
};

NodeTag

Union type of all PostgreSQL AST node type names:

type NodeTag = keyof Node;

Supported Node Types

This package works with all PostgreSQL AST node types defined in @pgsql/types, including:

• ParseResult - Root parse result from libpg-query
• SelectStmt - SELECT statements
• InsertStmt - INSERT statements
• UpdateStmt - UPDATE statements
• DeleteStmt - DELETE statements
• RangeVar - Table references
• ColumnRef - Column references
• A_Expr - Expressions
• A_Const - Constants
• And many more...

Integration with pgsql-parser

This package is designed to work seamlessly with the pgsql-parser ecosystem:

import { parse } from 'pgsql-parser';
import { visit } from '@pgsql/traverse';

const sql = 'SELECT name, email FROM users WHERE age > 18';
const ast = await parse(sql);

const visitor = {
  RangeVar: (node) => {
    console.log('Table:', node.relname);
  },
  ColumnRef: (node) => {
    console.log('Column:', node.fields?.[0]?.String?.sval);
  }
};

visit(ast, visitor);