[SR-11643] Xcode 11.2 beta 2 Regression: runtime crash with generic Foundation Encoder

[groue]

Previous ID	SR-11643
Radar	rdar://problem/56443094
Original Reporter	@groue
Type	Bug

Attachment: Download

Environment

Xcode Version 11.2 beta 2 (11B44) MacOS 10.14.6 (18G87)

Additional Detail from JIRA

| | | |------------------|-----------------| |Votes | 2 | |Component/s | Compiler | |Labels | Bug, 5.1Regression, RunTimeCrash | |Assignee | None | |Priority | Medium | md5: b518bac98f64f18f48b7a0e0d3852343

Issue Description:

Hello,

When an Encoder is generic and defined in a Swift Package library module, an Xcode app can't import this module and use this encoder without crashing right between the instantiation of the encoder and the call to the container(keyedBy: ) method, which is never called.

A reproducible case is available at http://github.com/groue/GRDBIssue636, and attached to this issue.

To reproduce:

1. Open the Crash/Crash.xcodeproject project with Xcode 11.2 beta 2

2. Run the app in an iOS simulator

3. Expected: the app crashes with a "not implemented" fatal error

4. Actual: the app crashes before the "not implemented" fatal error

Experiments reveal that the bug does not reproduce when the encoder is not generic.

Experiments reveal that the bug does not reproduce when the encoder is invoked from another swift package (run `swift build` and then `.build/debug/Crash` in order to see the expected "not implemented" fatal error, and not the unexpected crash.

This issue was first reported in https://github.com/groue/GRDB.swift/issues/636

[groue]

Cross-posted on Apple Feedback Assistant, since this may be an Xcode issue: FB7395337

[swift-ci]

Comment by Randy R (JIRA)

We found a workaround. Setting DEAD_CODE_STRIPPING = NO in our app’s target fixes the crash.

[swift-ci]

Comment by Caleb J (JIRA)

+1.

I'm also seeing this problem in Version 11.2.1 (11B500) Latest Mac AppStore Release. Setting `DEAD_CODE_STRIPPING=NO` also worked for me.