[SR-10191] Trap 6 during compilation instead of compile error

[g-Off]

Previous ID	SR-10191
Radar	rdar://49446040
Original Reporter	@g-Off
Type	Bug
Status	Resolved
Resolution	Done

Environment

Xcode 10.2 (10E125)
Apple Swift version 5.0 (swiftlang-1001.0.69.5 clang-1001.0.46.3)
Target: x86_64-apple-darwin18.5.0
mac

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, CompilerCrash
Assignee	@slavapestov
Priority	Medium

md5: 437e4e3eaad3b8123e8123fcf24ddf5a

relates to:

• SR-10648 Linker fails to link open method that was previously internal

Issue Description:

The following should produce a compiler error, but instead it produces an "Abort trap: 6" and the initial error starts off with

Global is external, but doesn't have external or weak linkage!
%swift.method_descriptor* @"$s7Shopify4BaseC8function33_72119E9B637C621F6419FCE57445EE94LLyyFTq"
<unknown>:0: error: fatal error encountered during compilation; please file a bug report with your project and the crash log
<unknown>:0: note: Broken module found, compilation aborted!

In File1.swift

class Base {
  fileprivate func function() { }
}

class Sub1: Base {
  override func function() { }
}

File2.swift

final class Sub2: Sub1 {
  override func function() { }
}

[belkadan]

Ooh, fun. @slavapestov, another version of the access control override issue.

[slavapestov]

#25190