Code coverage for safe navigation (?.) is different between node 20 and 22 when using @swc/jest

[everett1992]

When upgrading packages from node 20 to 22 some failed their jest coverage threshold. It happens in packages that use @swc/jest, in tests that use the save navigation operator, but don't test with null and non-null.

// lib.js
export function thing(obj) {
  return obj?.key
}

// test.js
//import { it } from 'node:test'
import { thing } from './lib.js'

it("tests thing", () => {
  thing({key: 1})
})

jest.config.mjs
export default {
  collectCoverage: true,
  transform: {
    '^.+\\.js$': ['@swc/jest'],
  },
}

// package.json
{"type":"module","dependencies":{"@swc/jest":"^0.2.38","jest":"^29.7.0"}}

$ mise exec node@22 --  npx jest
----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------|---------|----------|---------|---------|-------------------
All files |     100 |       50 |     100 |     100 |
 lib.js   |     100 |       50 |     100 |     100 | 2
----------|---------|----------|---------|---------|-------------------

$ mise exec node@20 --  npx jest
----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------|---------|----------|---------|---------|-------------------
All files |     100 |      100 |     100 |     100 |
 lib.js   |     100 |      100 |     100 |     100 |
----------|---------|----------|---------|---------|-------------------

I'm not sure if this should be considered a bug, in a sense it caught an uncovered branch. However, this will make it harder to upgrade to node 22

• node:test's --experimental-test-coverage was consistent between 20 and 22, but shows 100% branch coverage when only testing the non-null case, and 66% when only testing null.
• vitest was consistent and showed 100% coverage with both node versions
• jest without swc was consistent and showed 100% coverage with both node versions

[everett1992]

I was able to work around this by setting jsc target to es2020 or later

                jsc: {
                    target: "es2021",
                },

Tho this makes me think that @swc/jest is not setting the right default target. This table stops at node 17 but that was already es2022

[vs-cristian]

I was able to work around this by setting jsc target to es2020 or later

                jsc: {
                    target: "es2021",
                },

Tho this makes me think that @swc/jest is not setting the right default target. This table stops at node 17 but that was already es2022

worked for me

[everett1992]

I sent a PR to default unknown node versions to the previous known version https://github.com/swc-project/pkgs/pull/99