Babel support is broken in 26.4.2

💥 Regression Report

PR #2020 introduced a breaking change related to how Babel configuration is loaded. Previously, Babel configuration was loaded via the babelConfig option.

Last working version

Worked up to version: 26.4.1

Stopped working in version: 26.4.2

To Reproduce

Steps to reproduce the behavior:

• Have a valid .babelrc file at the root directory of the project
• Define rootDir as the root directory of the project

{
  …
  "globals": {
    "ts-jest": {
      "babelConfig": "<rootDir>/.babelrc"
    }
  },
  "rootDir": "./",
  …
}

$ yarn jest
yarn run v1.22.10
$ /Users/RA80533/lightning-banana/node_modules/.bin/jest
 FAIL   lightning-banana  src/index.spec.ts
  ● Test suite failed to run

    ENOENT: no such file or directory, open '<rootDir>/.babelrc'

      at ConfigSet._setupTsJestCfg (../../node_modules/ts-jest/dist/config/config-set.js:176:95)
      at new ConfigSet (../../node_modules/ts-jest/dist/config/config-set.js:152:14)
      at TsJestTransformer.createOrResolveTransformerCfg (../../node_modules/ts-jest/dist/ts-jest-transformer.js:95:38)
      at TsJestTransformer.getCacheKey (../../node_modules/ts-jest/dist/ts-jest-transformer.js:72:14)
      at ScriptTransformer._getCacheKey (../../node_modules/@jest/transform/build/ScriptTransformer.js:255:23)
      at ScriptTransformer._getFileCachePath (../../node_modules/@jest/transform/build/ScriptTransformer.js:289:27)
      at ScriptTransformer.transformSource (../../node_modules/@jest/transform/build/ScriptTransformer.js:428:32)
      at ScriptTransformer._transformAndBuildScript (../../node_modules/@jest/transform/build/ScriptTransformer.js:568:40)

Test Suites: 1 failed, 1 total
Tests:       0 total
Snapshots:   0 total
Time:        0.398 s
Ran all test suites.
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

Expected behavior

babelConfig should be read.

[ahnpnl]

In the scenario of babelConfig: true, the old codes will return

return {
      kind: 'file',
      value: undefined,
}

which is then go to this https://github.com/kulshekhar/ts-jest/blob/v26.4.1/src/config/config-set.ts#L378 . Because value is undefined, neither if path or else if path will execute, which will then return https://github.com/kulshekhar/ts-jest/blob/v26.4.1/src/config/config-set.ts#L398 and the final result is

{
    cwd: this.cwd
}

and for the refactored codes, the scenario babelConfig: true will end up here https://github.com/kulshekhar/ts-jest/blob/master/src/config/config-set.ts#L237

So both old codes and refactored codes are the same.

[RA80533]

I’ve isolated the issue to my use of Yarn workspaces:

• yarn workspaces run jest produces an issue in the workspace relying on Babel
• yarn workspace ${child} run jest configures Babel with the file in the directory of child

To be clear, the parent directory does not contain any Babel-related files whereas child does.

@ahnpnl I suppose this isn’t a regression issue then.