fix(babel): add retainLines to preserve source line numbers

[omarshibli]

Problem

The Playwright Inspector (PWDEBUG=1) highlights wrong source lines when debugging TypeScript tests that use destructured parameters.

Root cause: Playwright's babel transform does not set retainLines: true. Without it, babel's compact: false mode expands destructured parameters across multiple lines in the compiled output:

// Source (1 line):
test('my test', async ({ page }) => {

// Compiled without retainLines (3 lines):
test('my test', async ({
  page
}) => {

Each destructured pattern with N parameters expands from 1 line to N+2 lines. The Playwright Inspector uses compiled line numbers against the original source file without properly resolving through source maps, causing a cumulative line offset that grows with each destructured parameter pattern. For tests with multiple fixtures, the reported line can be off by 5-10+ lines.

Fix

Add retainLines: true to babel transform options in babelBundleImpl.ts. This tells babel to preserve the original line numbers in the compiled output by keeping statements on their original lines, eliminating the line drift entirely.

Testing

Added two test cases to tests/playwright-test/babel.spec.ts:

1. Line numbers in test report — Verifies that three tests using async ({ foo, bar, baz }) => destructured parameters report correct spec line numbers (8, 11, 14) instead of inflated values (~8, ~14, ~20).

2. Error location in test report — Verifies that a failing assertion inside a test with async ({ foo, bar }) => reports the correct error line (11) instead of an inflated value.

All existing babel tests continue to pass (10/10).

Related Issues

Fixes #19944
Fixes #26727

[omarshibli]

@microsoft-github-policy-service agree

[Skn0tt]

The tests are already green without the implementation change, and the referenced issues are also marked as fixed before this PR. If you experience a bug, please report it in a bug report first.

[omarshibli]

hey @Skn0tt , thanks for the input. but i do experience issues with debugging in chrome, the debugger isn't in sync with the source code. and i tried this fix locally fix yarn patch and it did fix my issue.