magic typescript function that returns its arguments' AST

index.ts

// This uses my modified version of typescript from my branch github.com/willmtemple/typescript#alchemy
import * as ts from "typescript/built/local/typescript";

import * as fs from "fs";
import * as os from "os";

import { promisify } from "util";

const readFile = promisify(fs.readFile);

interface CallSite {
  fileName: string;
  lineNumber: number;
  columnNumber: number;
}

/**
 * Gets the filename of the calling function
 */
function getCaller(): CallSite {
  const stack = new Error().stack.split("\n").slice(1);

  let relevantStackEntry = stack.filter(
    (s) => !s.includes(__filename) && s.includes(".ts")
  )[0];
  if (relevantStackEntry.includes("(")) {
    relevantStackEntry = relevantStackEntry.split("(")[1].split(")")[0];
  } else {
    relevantStackEntry = relevantStackEntry.split(" ").slice(-1)[0];
  }
  const site = relevantStackEntry.split(":");

  return {
    fileName: site[0],
    lineNumber: parseInt(site[1]),
    columnNumber: parseInt(site[2]),
  };
}

async function readFragmentToString(callSite: CallSite): Promise<string> {
  const content = (await readFile(callSite.fileName)).toString("utf-8");

  const relevantLines = content.split(os.EOL).slice(callSite.lineNumber - 1);
  relevantLines[0] = relevantLines[0].substring(callSite.columnNumber - 1);

  return relevantLines.join(os.EOL);
}

export async function getAsts(..._: any[]): Promise<Array<ts.Expression>> {
  const callSite = getCaller();

  const text = await readFragmentToString(callSite);

  console.log(text);

  ts.Parser.initializeState(
    "",
    text,
    ts.ScriptTarget.ESNext,
    undefined,
    ts.ScriptKind.TS
  );

  // Prime the scanner with a new token
  ts.Parser.nextToken();

  const expr = ts.Parser.parseExpression();
  console.log(expr);

  // Top level AST points to the call, so we know it will be a call expression
  // and have arguments.
  return (expr as any).arguments;
}

needs source map support and for the TS source to be available wherever the map lists it, as the source file is read by the implementation