xy-sql-formatter/src/parser/createParser.ts

Format whitespace in a SQL query to make it more readable

import nearley from 'nearley';

import Tokenizer from '../lexer/Tokenizer.js';
import { disambiguateTokens } from '../lexer/disambiguateTokens.js';
import { ParamTypes } from '../lexer/TokenizerOptions.js';
import { StatementNode } from './ast.js';
import grammar from './grammar.js';
import LexerAdapter from './LexerAdapter.js';
import { createEofToken } from '../lexer/token.js';

const { Parser: NearleyParser, Grammar } = nearley;

export interface Parser {
  parse(sql: string, paramTypesOverrides: ParamTypes): StatementNode[];
}

/**
 * Creates a parser object which wraps the setup of Nearley parser
 */
export function createParser(tokenizer: Tokenizer): Parser {
  let paramTypesOverrides: ParamTypes = {};
  const lexer = new LexerAdapter(chunk => [
    ...disambiguateTokens(tokenizer.tokenize(chunk, paramTypesOverrides)),
    createEofToken(chunk.length),
  ]);
  const parser = new NearleyParser(Grammar.fromCompiled(grammar), { lexer });

  return {
    parse: (sql: string, paramTypes: ParamTypes) => {
      // share paramTypesOverrides with Tokenizer
      paramTypesOverrides = paramTypes;

      const { results } = parser.feed(sql);

      if (results.length === 1) {
        return results[0];
      } else if (results.length === 0) {
        // Ideally we would report a line number where the parser failed,
        // but I haven't found a way to get this info from Nearley :(
        throw new Error('Parse error: Invalid SQL');
      } else {
        throw new Error(`Parse error: Ambiguous grammar\n${JSON.stringify(results, undefined, 2)}`);
      }
    },
  };
}