Typescript project reference

[rrousselGit]

🙋 feature request

With typescript 3.0.0 there's now something called "Project reference". It basically links multiple ts packages together in mono-repository. And build them in order in a single tsc call.

https://www.typescriptlang.org/docs/handbook/project-references.html

Faster build time, cool and all. But it requires a custom flag to tsc : tsc -b

🤔 Expected Behavior

Parcel detects that there's project reference activated and pass -b flag

😯 Current Behavior

-b flag isn't passed. Therefore dependencies are not built. Leading to

Cannot resolve dependency "my-dependency"

💁 Possible Solution

If the tsconfig.json contains references field, add -b flag
As a workaround, we can manually call tsc -w -b on another terminal. But then that's the equivalent of not using parcel

🔦 Context

Simply setting up a project with "Project references".

💻 Examples

WIP

[DeMoorJasper]

Well parcel isn't even running typescript 3 yet, perhaps we should start with simply upgrading to 3 first

[rrousselGit]

Isn't it?

I used other typescript 3 features with parcel today (spread operator with tupples). Worked perfectly.

Interesting.

[DeMoorJasper]

That's pretty cool, parcel localRequires it so it just uses whatever the user has installed. Means ts 3 doesn't have that many changes that would break parcel's implementation. We currently test against typescript 2.9.

It's mainly a thing of running ts 3 in the tests to make sure everything still works, I'll create a PR in a bit

[rrousselGit]

According to typescript documentation, the only breaking change is unknown now being a reserved keyword

https://github.com/Microsoft/TypeScript-wiki/blob/master/Breaking-Changes.md

In the mean time, I'll try to make a fork that adds that -b flag and see what happens.

[DeMoorJasper]

Awesome, thanks for looking that up.
I had just ran all tests against 3.0 and seems to be all good :)

Update PR: #1840

[rrousselGit]

Tried adding build: true in TypeScriptAsset.js on a parcel fork.

Doesn't seems to do anything. I expected as much considering it seems we must use tsc cli to pass that flag.

Maybe it's something on typescript side. Like supporting a build to compilerOptions (weird it's not there)

[rrousselGit]

microsoft/TypeScript#25613

It seems voluntary on TS side that --build flag can't be set using compilerOptions. I wonder what we can do here

[DeMoorJasper]

Well that's a pity, although I'm not sure if this would be able to work inside parcel at all as parcel compiles one file at a time and gives typescript very little information.

[rrousselGit]

Yeah, I realized that. Maybe we can have a middle ground.
Where typescript would list module dependencies and parcel add them to the build list. Or maybe just parse the references object.

I don't know. But this would be quite cool if this was supported by parcel. We wouldn't need to have one watcher per package.

Edit: I came across collectDependecies method in Asset class which can be overridden.
Somehow it should be possible to add the baseUrl/index.tsx? of each reference as dependency.

But I wonder how parcel would handle going outside of the current package boundaries.

[rrousselGit]

From Ryan Cavanaugh as an answer to "How to compile projets references with transpileModule api ?"

If you want to read the references from the tsconfig to walk the dependency graph and build upstream projects, you can call ts.createSolutionBuilder and then call getBuildGraph to get a representation of the dependency tree you can traverse.

Would this be ok to do that in parcel ?

[DeMoorJasper]

Probably better to contribute this to parcel-plugin-typescript as that's a more complete and advanced version of ts than parcel's internal implementation.