Default values for jsconfig.json override extended values

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

src/compiler/commandLineParser.ts の、issue で参照されている jsconfig のデフォルト値の処理から始めます。2 つの設定で問題を再現し、それぞれについて npx tsc -p ... --showConfig を比較します。拡張された設定で明示的に定義された値が、jsconfig のデフォルト値に置き換えられず保持されれば完了です。