school_compare/nextjs-app/__tests__/components/noEmDashCopy.test.ts

import fs from 'fs';
import path from 'path';
import ts from 'typescript';

/**
 * Keeps the em dash out of public copy.
 *
 * Every visitor-facing sentence was rewritten to use a colon, comma, full stop
 * or parentheses instead. A new one slips back in unnoticed, because it reads
 * fine to whoever wrote it, so this walks the source with the TypeScript parser
 * and checks every string literal, template chunk and JSX text node. Comments
 * are not nodes the walk visits, so they stay free to use it.
 *
 * Two uses are allowed:
 *  - a lone dash standing in for a missing value in a table cell or stat slot,
 *    which is a data convention rather than prose;
 *  - the message of a thrown Error, which only a developer reads.
 */

const ROOT = path.join(__dirname, '..', '..');
const SCANNED = ['app', 'components', 'lib'];
const SKIPPED = [path.join(ROOT, 'app', '(payload)')];

function sources(dir: string): string[] {
  if (SKIPPED.includes(dir)) return [];
  return fs.readdirSync(dir, { withFileTypes: true }).flatMap((entry) => {
    const full = path.join(dir, entry.name);
    if (entry.isDirectory()) return sources(full);
    return /\.tsx?$/.test(entry.name) ? [full] : [];
  });
}

function isErrorMessage(node: ts.Node): boolean {
  for (let p = node.parent; p; p = p.parent) {
    if (ts.isNewExpression(p) && /Error$/.test(p.expression.getText())) return true;
    if (ts.isStatement(p)) return false;
  }
  return false;
}

const EMPTY_VALUE = /^(—|—)$/;

function dashedCopy(file: string): string[] {
  const text = fs.readFileSync(file, 'utf8');
  const kind = file.endsWith('.tsx') ? ts.ScriptKind.TSX : ts.ScriptKind.TS;
  const sf = ts.createSourceFile(file, text, ts.ScriptTarget.Latest, true, kind);
  const found: string[] = [];
  const visit = (node: ts.Node) => {
    if (
      ts.isStringLiteral(node) || ts.isNoSubstitutionTemplateLiteral(node) || ts.isJsxText(node)
      || ts.isTemplateHead(node) || ts.isTemplateMiddle(node) || ts.isTemplateTail(node)
    ) {
      const copy = node.getText().replace(/\s+/g, ' ').trim();
      const bare = node.text.trim();
      if (/—|—/.test(copy) && !EMPTY_VALUE.test(bare) && !isErrorMessage(node)) {
        const { line } = sf.getLineAndCharacterOfPosition(node.getStart());
        found.push(`${path.relative(ROOT, file)}:${line + 1}  ${copy}`);
      }
    }
    ts.forEachChild(node, visit);
  };
  visit(sf);
  return found;
}

describe('public copy', () => {
  it('uses no em dashes', () => {
    const files = SCANNED.flatMap((dir) => sources(path.join(ROOT, dir)));
    expect(files.length).toBeGreaterThan(50);
    expect(files.flatMap(dashedCopy)).toEqual([]);
  });
});