Regarding new "incremental" flag from TS 3.4

[goenning]

Typescript 3.4 (RC) includes a new "incremental" flag: https://devblogs.microsoft.com/typescript/announcing-typescript-3-4-rc/

I've updated to 3.4 and set this flag to true.

If I do tsc -p tsconfig.json then the build cache is generated and subsequent calls are much faster.

But if I run it through webpack (which is using ts-loader), then the build cache is not generated and subsequent calls take about the same time as previously.

Does ts-loader need to be changed in order to support it?

[johnnyreilly]

Possibly - I haven't looked at it yet and so can't advise. If you'd like to look into it that'd be amazing!

[Jojoshua]

I was just about to open this issue. I also tried specifying compilerOptions: { incremental: true } but no dice.

[MadaraUchiha]

TypeScript 3.4.1 had officially landed. Can this feature be safely (or at all) used?

[johnnyreilly]

I suspect work may need to be done to add support. If someone wants to take a look that'd be greatly appreciated!

[radiosterne]

Looking into it, we may be able to pass specialized incrementalHost to createProgram based on the flag.

[johnnyreilly]

Awesome - thanks!

[radiosterne]

As of now, I see no clean way to use TSC's incremental :(

Every API they are using to scaffold incremental building is, sadly, non-public, if I'm not missing something.

@johnnyreilly, what's your take on our subsequent steps here? I propose opening an issue in Typescript repository in order to make these APIs public. But, of course, we can do it dirty and just use private APIs (by extending ts with our own typings) — which I would not recommend :)

[johnnyreilly]

@radiosterne thanks for investigating! I really appreciate it.

I'd recommend opening an issue with against the TypeScript repo to see if they're interested in making the API public facing. It's not unusual for them to release a feature like this and then "API release" it later. If memory serves, the original incremental build API was released with something like TypeScript 2.6 with the API not shipping until maybe 2.8 or so.

It's worth starting the conversation and linking back to this issue for context.

[radiosterne]

Now that I've filed an issue with them and my head cleared a bit, I'm starting to wonder if we're gonna be able to employ this API at all.

The sole purpose of incremental flag, as I see it, is to speed up cold builds (webpack watch is covered by ts-loader already) by omitting non-changed files from compilation altogether (but still type-checking them, if they are using something from changed files).

Isn't it it our responsibility on cold build to compile each and every file, even if it's unchanged, in order to pass compilation result down to webpack for bundling? Or am I missing something here?

[MadaraUchiha]

I'm unsure of how the API functions, but is it not the case that it caches compilation results and gives you a faster lookup in case of cache hits? Without seeing the code, I'd naively expect the API to look the same for the consumer. (i.e. the cache layer being invisible)

[johnnyreilly]

Isn't it it our responsibility on cold build to compile each and every file, even if it's unchanged, in order to pass compilation result down to webpack for bundling? Or am I missing something here?

I haven't had chance to look into incremental yet and so you probably understand it better than I do. That said, my assumption is that incremental speeds up cold builds using data saved to disk during previous compilations. I don't see any reason that shouldn't be used by ts-loader on startup as well... (Always possible I may be misunderstanding it.)

[glen-84]

microsoft/TypeScript#29978

[johnnyreilly]

It looks like APIs will be exposed with a future version of TS. When those are available we'd greatly welcome PRs that plug into this. 😁