noEmit and skipLibCheck should be on by default in TS compiler options

This is a related issue to #352. The build script works with rollup.js, not tsc, so the noEmit option should be enabled by default. Users running npx tsc shouldn’t expect to have to specify --noEmit, because using tsc is a normal part of TS development. Currently npx tsc will clutter the src directory with transpiled files, which can be difficult to clean up if there are uncommitted changes mixed in.

This is important because without tsc there is no way to do project-wide type checking. The build script will only stop at the first error. The test runner will report errors, but only for files that are tested, and it’s also the wrong place for type checking (#521).

[orta]

This thread winds through a few topics, so I’ll give my ideas in short-form

• I don’t think skipLibCheck should be enabled for users by default, personally. The flag explicitly breaks some of the type system contracts and is available if you need it, but that should be edge-cases not for everyone.

• I’m a believer in using babel for transpiling and ts for type-checking when dealing with web. As a pragmatist, you probably already have babel in the tree, and it keeps build tools consistent. I’m personally against having types checking happening in tests, because I wouldn’t want them blocking running a test. Whether using ts-jest or ts-babel is generally

• WRT incremental / build mode etc - these are useful for when TS is emitting the .js files in composite projects - which probably isn’t happening in your watch mode which needs to go through rollup?

• the OP on noEmit makes sense to me, given that it would be surprising to me too to see a bunch of ts files.

[jaredpalmer]

This is a really good discussion. Learned a lot about TS!

A bit of history, when I made TSDX I made one change to how Formik’s build system worked: rpts2. OG pre-tsdx Formik used to use a two-step build (because Babel TS didn’t really exist yet). First it would use tsc and emit esnext js to a temp directory. Then rollup would bundle the temp directory to dist (so it could use Babel plugins). It’s very possible that I incorrectly kept around some TS config options that became redundant by switching to rpts2 but never noticed because “it just worked.” — FWIW, my course of action with libraries and apps differs with respect to incorrect dependency types. When writing an app, I will 100% use patch-package to fix the types. I want to check my deps. During dev/watch, I’m fine with foregoing dep checks on large projects, but prefer it if possible. During builds, I want as much type safety as possible. When making a lib, however, I don’t think patch package is acceptable. So I usually will fork the dep and publish my own corrected version or copy it into my libs source (with proper correction) if it’s small enough. Until reading this thread, I never considered skiplibCheck for libs, but maybe I should have. I usually err on the side of strictness and correctness over build performance. —- I think the question we want to answer is what the default behavior should be for novice and intermediate typescript folks. We will obviously have to document this somewhere in an “advanced config” section

cc’ing typescript team for their suggestion @orta

tl;dr we are debating what defaults should be for noEmit, skiplibCheck, incremental builds, and emitDeclaration given how rollup-plugin-typescript2 works.