Attachment: Download

$ sw_vers
ProductName: Mac OS X
ProductVersion: 10.15.4
BuildVersion: 19E266

$ xcodebuild -versionXcode 11.4
Build version 11E146

$ swift --version
Apple Swift version 5.2 (swiftlang-1103.0.32.1 clang-1103.0.32.29)
Target: x86_64-apple-darwin19.4.0

$ swift build --version
Swift Package Manager - Swift 5.2.0

Issue Description:

EDIT:
I asked for help in Swift Forums. There I got the explanation for my issue. I was using the same name for two of the packages in the dependency graph. I am not sure if I should close this bug or not. Because I believe that SwiftPM could fail in a more controlled way and give more helpful feedback when there is a clash in packages names.

When I add a specific dependency to my Package.swift (https://github.com/hectr/swift-http-client.git) file, SPM stops working (It cannot resolve package dependencies):

$ swift package resolve
Fatal error: 'try!' expression unexpectedly raised an error: TSCBasic.GraphError.unexpectedCycle: file /Library/Caches/com.apple.xbs/Sources/swiftpm/swiftpm-16074/Sources/Workspace/Workspace.swift, line 1112
zsh: illegal hardware instruction  swift package resolve

I attempted to use the dependency using a tag, the branch name and a local folder in my machine, but the outcome was the same. Renaming the library didn't help either.

I have tried to create the minimal project to reproduce the issue in my machine (Package.zip).

I am going to explain also how the issue started, just in case it is useful:

I am building an iOS application. My setup consists of a workspace that contains:

• a project with the application's target

• a Package.swift file

I also use CocoaPods, but I think it is not relevant to this issue.

I use the Package.swift file to add external dependencies and to create local libraries that I then add to the application target.

See the file layout:

.
├── Application
│   ├── MyApp/
│   └── MyApp.xcodeproj/
├── Package
│   ├── Package.swift
│   ├── Sources/
│   └── Tests/
├── MyApp.xcworkspace/
└── ...

I do most of the development opening the workspace and editing the source files and the Package.swift file.

After adding as a dependency the library https://github.com/hectr/swift-http-client.git, Xcode crashed. It kept crashing consistently each time I opened it. See the attached crash report.

If I remove the dependency, Xcode stops crashing.