Show a useful error message if you try to build lambdas on MacOS

[benjyw]

Right now it fails in all sorts of subtle ways relating to failures to resolve requirements and picking weird interpreters (e.g., due to the issue explained in pex-tool/pex#957).

It hypothetically possible to build lambdas on MacOS if all transitive requirements have prebuilt linux wheels, but that is too narrow a case to support, and it's subtle and tricky to get right even if we wanted to. Better to just say no in a helpful and explicit way.

[riisi]

@benjyw Started looking at this. Were you thinking a logger.error message or raising an exception - I'm not sure what the convention is elsewhere.

[kaos]

@riisi I think you want to raise an exception, in order to not proceed with the build.
Edit: including the helpful message in the exception..

[riisi]

Got it, thanks. Will draft something soon.

…

On Mon, 22 Nov 2021 at 10:33, Andreas Stenius ***@***.***> wrote: @riisi <https://github.com/riisi> I think you want to raise an exception, in order to not proceed with the build. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#11941 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AHGSB3ER2YC772B5VMBS62LUNIL7FANCNFSM43D3HQ5Q> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>.

[Eric-Arellano]

I think you could use FallibleProcessResult instead of ProcessResult so that the error is not eager, and then inspect the error code and error message to determine dynamically if you should mention macOS as a culprit?

Or as a first step, you could always include that macOS warning if the user is on macOS, but use "hedge words"—like "may" or "it's possible"—to make clear that that is only one possible reason the build failed.

[benjyw]

I don't think parsing error messages is great, there are so many different errors that can occur. On error we can check the platform and mention MacOS as a likely culprit.

[riisi]

Managed to replicate this locally (i.e. building a lambda with package without a wheel on mac). I was initially assuming that it would be possible to try/catch in the lambda rule, however, I now understand that depends on `FallibleProcessResult`. It looks like the `build_pex` rule would need to be modified - in which case should this warning be logged there, and be applicable for packaging pex as well as lambdas? Unless there's another way to catch rule engine errors that I'm missing?

…

On Mon, 22 Nov 2021 at 17:48, Benjy Weinberger ***@***.***> wrote: I don't think parsing error messages is great, there are so many different errors that can occur. On error we can check the platform and mention MacOS as a likely culprit. — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#11941 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AHGSB3BRCZWAAMONGMHDGV3UNJ65DANCNFSM43D3HQ5Q> . Triage notifications on the go with GitHub Mobile for iOS <https://apps.apple.com/app/apple-store/id1477376905?ct=notification-email&mt=8&pt=524675> or Android <https://play.google.com/store/apps/details?id=com.github.android&referrer=utm_campaign%3Dnotification-email%26utm_medium%3Demail%26utm_source%3Dgithub>.

[Eric-Arellano]

Yeah, build_pex would need to be modified to use FallibleProcessResult, which is almost never what we want. It's convenient that the result is a built PEX and callers don't need to handle the failure case.

Instead, I think I still recommend this:

Or as a first step, you could always include that macOS warning if the user is on macOS, but use "hedge words"—like "may" or "it's possible"—to make clear that that is only one possible reason the build failed.

Basically use logger.warning() with a variant of the warning info box at https://www.pantsbuild.org/docs/awslambda-python#step-3-run-package.

(We assume some users do not read the docs. Our UX and error messages should be good enough that you can figure things out on your own. At least, that's the aspiration!)