Default values for jsconfig.json override extended values

[yo1dog]

TypeScript Version: 3.8.0-dev.20200207

Search Terms: jsconfig extend override defaults

Code

// a/jsconfig.json
{
  "files": ["test.js"],
  "compilerOptions": {
    "maxNodeModuleJsDepth": 0
  }
}

// b/jsconfig.json
{
  "extends": "../a/jsconfig.json"
}

// a/test.js
console.log("hello");

Reproduce

mkdir -p a b
echo '{"files":["test.js"],"compilerOptions":{"maxNodeModuleJsDepth":0}}' > a/jsconfig.json
echo '{"extends":"../a/jsconfig.json"}' > b/jsconfig.json
echo 'console.log("hello");' > a/test.js

npx tsc -p a/jsconfig.json --showConfig
npx tsc -p b/jsconfig.json --showConfig

Expected behavior:
Both implied configs A and B have compilerOptions.maxNodeModuleJsDepth: 0.

Actual behavior:
Implied config A has compilerOptions.maxNodeModuleJsDepth: 0.
Implied config B has compilerOptions.maxNodeModuleJsDepth: 2.
Output:

{
    "compilerOptions": {
        "allowJs": true,
        "maxNodeModuleJsDepth": 0,
        "allowSyntheticDefaultImports": true,
        "skipLibCheck": true,
        "noEmit": true
    },
    "files": [
        "./test.js"
    ]
}
{
    "compilerOptions": {
        "allowJs": true,
        "maxNodeModuleJsDepth": 2,
        "allowSyntheticDefaultImports": true,
        "skipLibCheck": true,
        "noEmit": true
    },
    "files": [
        "../a/test.js"
    ]
}

Implied config B has maxNodeModuleJsDepth: 2 despite it extending config A which explicitly sets maxNodeModuleJsDepth: 0.

Possible cause
This may be caused by the default values for config files named jsconfig.json overriding the values from the extended config. maxNodeModuleJsDepth: 2 is one of the default values. See: /src/compiler/commandLineParser.ts#L2459

Solution
Default values for jsconfig.json config files should not override values explicitly defined by the extended configs.

Workaround
Explicitly set the following values in config files named jsconfig.json that extend other configs with non-default values:

• allowJs
• maxNodeModuleJsDepth
• allowSyntheticDefaultImports
• skipLibCheck
• noEmit

[MartinJohns]

You can pass the --showConfig compiler flag to see the final configuration.

https://www.typescriptlang.org/docs/handbook/compiler-options.html

Rather than actually execute a build with the other input options and config files, show the final implied config file in the output.

This will print:

{
    "compilerOptions": {
        "noEmit": true,
        "outDir": "./out",
        "allowJs": true,
        "maxNodeModuleJsDepth": 2,
        "allowSyntheticDefaultImports": true,
        "skipLibCheck": true
    },
    "files": [
        "./test.js"
    ]
}

[yo1dog]

Awesome. Thanks for this tip. I updated my ticket to include this and a simpler test case.

[yo1dog]

Any feedback on this? I have a pull request ready.

[orta]

Yeah, this feels like a legit bug to me 👍