feat: please support the "extends" setting in tsconfig.json (configuration inheritance)

[atamocius]

It would be nice if the extends property of tsconfig.json was supported.

I found out the hard way that it wasn't supported. I was getting an Uppercase/lowercase mismatch error. I found out that it was because my tsconfig.json was using the extends property to inherit from a common config file where the baseUrl was defined.

[erikbarke]

Hey @antonmata, I modified the typescript-latest example project like this:

Karma config:

module.exports = function(config) {
    config.set({

        frameworks: ["jasmine", "karma-typescript"],

        files: [
            { pattern: "src/**/*.ts" }
        ],

        preprocessors: {
            "**/*.ts": ["karma-typescript"]
        },

        karmaTypescriptConfig: {
            tsconfig: "./tsconfig.json"
        },

        reporters: ["dots", "karma-typescript"],

        browsers: ["Chrome"]
    });
};

tsconfig.json:

{
    "extends": "./base-tsconfig.json",
    "compileOnSave": false,
    "exclude": [
        "node_modules"
    ]
}

base-tsconfig.json (this is a new file I created for this test):

{
    "compilerOptions": {
        "module": "commonjs",
        "noImplicitAny": true,
        "outDir": "tmp",
        "target": "ES5",
        "sourceMap": true,
        "types" : [
            "jasmine"
        ]
    }
}

Does this describe your scenario? It works when I run npm test, I can change settings in base-tsconfig.json to change the compiler behavior.

Are you on an OS with a case sensitive file system? The "Uppercase/lowercase mismatch" error is thrown by the dependency walker if a module is imported with a different case than its file name, ie import { Service } from "./service"; from the file Service.ts, so you probably have a mismatch somewhere in your code.

[atamocius]

The key item for me was the baseUrl. To best describe my scenario, you need to add the baseUrl in base-tsconfig.json and also define appropriate resolve.modules in webpack:

resolve: {
    extensions: [".tsx", ".ts", ".js", ".json"],
    modules: [
        __dirname,
        "node_modules"
    ]
}

I kind of figured out that it could be a path issue because I was getting a Error: Uppercase/lowercase mismatch message from an error thrown in dependency-walker.ts.

[atamocius]

I forgot to mention that I was able to workaround the issue by explicitly defining the baseUrl in the "child" tsconfig.json that was referenced by karma-typescript, essentially bypassing the inheritance.

[erikbarke]

I was able reproduce the error and this is probably a Typescript bug, microsoft/TypeScript#17617.

The compiler seems to lowercase module names if the baseUrl property is set in a tsconfig that is inherited, just like what you're describing.

This triggers the case sensitivity validators in both karma-typescript and the Typescript compiler, if you're using the forceConsistentCasingInFileNames compiler option.

[atamocius]

Ah ok, that explains a lot. I was so confused that the error message was showing both paths, but they look alike except for just the casing. I really did not know what or how to fix that, hence just went for the workaround. Thanks for looking into this.