How do I fail a build from a resolver plugin?

[Aaronius]

Hello! I'm creating a resolver plugin. When a certain file is required, I would like my plugin to be able to fail the build rather than allow the asset to continue to the next resolver. How would I do this? I can throw a ThrowableDiagnostic, which results in a failed build if my resolver is the only resolver in the pipeline, but if there are subsequent resolvers in the pipeline that can resolve the dependency, then my ThrowableDiagnostic does not fail the build. How would I accomplish what I'm trying to do? Thanks!

[DeMoorJasper]

Currently that's impossible as the way it works is that a thrown error will result in the next resolver getting a chance to resolve the asset as an error usually means that it can't resolve it.

We might add a flag or something similar to it that we can use like the MODULE_NOT_FOUND in the standard node resolver, so we know what kind of error occurred although not entirely sure what the best approach for this is.

[mischnic]

not entirely sure what the best approach for this is.

Making the return type Promise<Diagnostic | ?ResolveResult> (for the cases where the default resolver throws) and making throwing errors actually fail the build?

[DeMoorJasper]

Yeah, was also thinking about something like this as a possible solution. Maybe we should do this while we're in beta? Would be more expected than a throw doing nothing

[Aaronius]

FWIW, throwing a regular error is the first thing I tried. That was before I knew about ThrowableDiagnostic, which is the second thing I tried.

[DeMoorJasper]

Errors can be converted into diagnostics really easily so it should both work if we end up changing this

[Aaronius]

Thanks. Even though it's not the answer I was hoping for, it's definitely helpful. In case it helps to hear our use case, we are creating bundles of untrusted, third-party code (which we call extensions). We want to allow the third-party code to import/require other files that the third-party provided but not any arbitrary file on the server. We also want the third-party code to be able to import/require certain npm packages, but not others. I was hoping to set up my resolvers in my .parcelrc like this: "resolvers": ["parcel-resolver-limit-extension-dependencies","@parcel/resolver-default"], where parcel-resolver-limit-extension-dependencies would be able to fail the build if the extensions depended on something that isn't allowed.

I'll probably either try to call @parcel/resolver-default directly from parcel-resolver-limit-extension-requires if the thing being required is allowed OR I'll write a babel plugin that detects imports/requires and fails the build if an infraction is found (throwing an error from a Babel plugin does fail the build).

[DeMoorJasper]

This seems like a valid use-case, maybe we should change the API to allow this like @mischnic mentioned

[Aaronius]

@DeMoorJasper @mischnic Is this being tracked somewhere already or should I create an issue for it?

[mischnic]

Here was the issue: #5012
PR is already merged