--config [JSON] + projects doesn't seem to work

🐛 Bug Report

When passing serialized JSON for the --config option that contains projects, I get the following error:

Error: Jest: Cannot use configuration as an object without a file path.
    at readConfig (~/github/benmvp/benmvp-cli/node_modules/jest-config/build/index.js:139:13)
    at projects.filter.map.root ~/github/benmvp/benmvp-cli/node_modules/jest-cli/build/cli/index.js:487:62)
    ....

The parsed JSON looks like:

{
    "projects": [
        {
            "moduleFileExtensions": ["ts", "js"],
            "transform": {
                "^.+\\.(ts|js)$": "babel-jest"
            },
            "testMatch": [
                "<rootDir>/src/**/*.ts"
            ],
            "runner": "jest-runner-tsc",
            "displayName": "typescript"
        },
        {
            "moduleFileExtensions": ["ts", "js"],
            "transform": {
                "^.+\\.(ts|js)$": "babel-jest"
            },
            "testMatch": [
                "<rootDir>/src/**/*.spec.ts"
            ],
            "displayName": "test"
        }
    ],
    "rootDir": "."
}

To Reproduce

Just run:

npx jest --config '{"projects":[{"moduleFileExtensions":["ts","js"],"transform":{"^.+\\.(ts|js)$":"babel-jest"},"testMatch":["<rootDir>/src/**/*.ts"],"runner":"jest-runner-tsc","displayName":"typescript"},{"moduleFileExtensions":["ts","js"],"transform":{"^.+\\.(ts|js)$":"babel-jest"},"testMatch":["<rootDir>/src/**/*.spec.ts"],"displayName":"test"}],"rootDir":"."}'

Expected behavior

I expect to be able to run the projects just like if they were defined in a config file (which does work).

Link to repl or repo (highly encouraged)

See repro command. Happy to contribute a PR, I just don’t know what to fix. 😄

Run npx envinfo --preset jest

Paste the results here:

  System:
    OS: macOS High Sierra 10.13.6
    CPU: (4) x64 Intel(R) Core(TM) i5-5257U CPU @ 2.70GHz
  Binaries:
    Node: 10.12.0 - ~/.nvm/versions/node/v10.12.0/bin/node
    Yarn: 1.12.3 - /usr/local/bin/yarn
    npm: 6.4.1 - ~/.nvm/versions/node/v10.12.0/bin/npm
  npmPackages:
    jest: ^23.6.0 => 23.6.0

Debugging

1/ I tried moving the JSON back to a .js file and it works (my current workaround). I need the contents to be dynamic, which is why I want to pass JSON

2/ I did a whole bunch of code spelunking to try to get it to work. I narrowed down the problem to readConfigs in jest-config. It seems that after successfully parsing the JSON, it maps over each project to readConfig on each (passing configPath). The problem is that configPath is null so readConfig complains. And the reason configPath is null is because when the JSON was originally parsed (also by readConfig), I guess there is no configPath to set so it remains null. That’s as far as I got since I don’t understand the why of the code.

[rickhanlonii]

Hey @benmvp thanks for filing! Confirmed - I’ll take a look

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