Rewritten from scratch with some additional error checking and lipo -info output in the case where an architecture isn't present.

There is no sense in doing this is in non-release modes.

Is there a foolproof way of detecting release vs non-release builds? CONFIGURATION won't be safe since developers can rename them at will. It'd be relatively simple to rule it out for simulator builds with a check against CURRENT_PLATFORM == iphonesimulator but that doesn't cover device debug builds. There are probably a few other heuristics we could use (like whether debug symbols are enabled), but given that it takes ~0.4s to run this (with just the Flutter framework), I wonder if the additional complexity is worth it.

Fixes #7908.

lgtm. I guess if it is fast enough, it doesn't matter.

sgtm. I've got a followup that rewrites all the thin command in Dart. Will get the build code and tests done and send as a followup patch.

That work still needs a bit of performance tuning; the runtime is ~1.2s vs 0.4s for the shell version. Will take a look at whether snapshotting helps significantly and if so, we can do what we do with the flutter tool.

I may be reading incorrectly but wouldn't this cause issues with armv7 users if we declare support for standard architectures but stripped out armv7 from libraries?

Part of this patch was to change the ARCHS setting from 'Standard architectures' to arm64. We don't update VALID_ARCHS, but given that Xcode only builds the intersection of VALID_ARCHS and ARCHS, we should be okay. (Personally I'd like to get armv7 builds working and revert 388280f.

Ah, understood