Another bizarre thing about this bug is that it seems to be quite intermittent. Our CI system has several fastlane "lanes" that each get built on a separate Mac. For reasons unknown, sometimes they will fail with the above-mentioned error, where SPM acts like like SwiftProtobuf doesn't exist:
/REDACTED/TensorManifold/Sources/TensorManifold/base.pb.swift:13:8:
error: no such module 'SwiftProtobuf'
import SwiftProtobuf
I can assure you in all these cases, SwiftProtobuf.xcframework does in fact exist, and the path "lib/SwiftProtobuf.xcframework" is a valid path (it's a symlink to where the actual XCFramework is kept).
Can anyone think of a reason why this should fail intermittently like that?