Support using --module and --outDir flags in conjunction with --build

Search Terms

--build --module --outDir

Suggestion

I would like to be able to pass --module and --outDir, in --build mode so that I can have multiple npm scripts for different build outputs without needing multiple tsconfig files.

Use Cases

In Aurelia vNext we've fully adopted the new 3.0 build system and are starting to prepare for publishing. We want to publish the build outputs for all different module systems (for all packages) so that consumers can easily point to the one that's compatible with their project.

We have been able to do this pre-3.0 like so:

    "build:commonjs": "tsc -m commonjs --outDir dist/commonjs",
    "build:amd": "tsc -m amd --outDir dist/amd",
    "build:system": "tsc -m system --outDir dist/system",
    "build:umd": "tsc -m umd --outDir dist/umd",
    "build:es2015": "tsc -m es2015 --outDir dist/es2015",

Now when trying to do this, it doesn't work:

    "build:commonjs": "tsc -b -m commonjs --outDir dist/commonjs",
    "build:amd": "tsc -b -m amd --outDir dist/amd",
    "build:system": "tsc -b -m system --outDir dist/system",
    "build:umd": "tsc -b -m umd --outDir dist/umd",
    "build:es2015": "tsc -b -m es2015 --outDir dist/es2015",
    "build:esnext": "tsc -b -m esnext --outDir dist/esnext",

Results in:

message TS6096: File (...)/packages/runtime/-m' does not exist
message TS6096: File (...)/packages/runtime/commonjs' does not exist

And nothing else happening. I read in the docs that only 4 particular flags are supported in conjunction with --build so it seems this is simply not implemented.

Examples

We'd like to have something like this in the packages package.json:

    "build:commonjs": "tsc -b -m commonjs --outDir dist/commonjs",
    "build:amd": "tsc -b -m amd --outDir dist/amd",
    "build:system": "tsc -b -m system --outDir dist/system",
    "build:umd": "tsc -b -m umd --outDir dist/umd",
    "build:es2015": "tsc -b -m es2015 --outDir dist/es2015",
    "build:esnext": "tsc -b -m esnext --outDir dist/esnext",
    "build": "run-p build:*",

And when calling npm run build from the top-level package (using lerna...), that would produce build outputs in all module formats for all packages

Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript / JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. new expression-level syntax)

Start by reviewing the documented flags supported with --build and reproduce the reported TS6096 behavior using the example commands. Done means --module and --outDir work with --build and produce the requested module-format outputs without requiring multiple tsconfig files.