[SR-9734] SPM get stuck in an infinite loop

[0xTim]

Previous ID	SR-9734
Radar	None
Original Reporter	@0xTim
Type	Bug

Environment

macOS 10.14.2 Apple Swift version 4.2.1 (swiftlang-1000.11.42 clang-1000.11.45.1) Target: x86_64-apple-darwin18.2.0

Additional Detail from JIRA

| | | |------------------|-----------------| |Votes | 0 | |Component/s | Package Manager | |Labels | Bug | |Assignee | None | |Priority | Medium | md5: 82a76cb7edafea119cb7c88af560b918

Issue Description:

When running swift package resolve with the following manifest, it gets stuck in an infinite loop. The reason is that fluent-postgresql is only a major version 1, 3.0.0 doesn't exist yet.

Steps to reproduce:

1. Create empty SPM project

2. Set Package.swift to the following:
   // swift-tools-version:4.2
import PackageDescription``let package = Package(
   {{ name: "name",}}
   {{ dependencies: [}}
   {{ .package(url: "https://github.com/vapor/vapor.git", from: "3.0.0"),}}
   {{ .package(url: "https://github.com/vapor/fluent-postgresql.git", from: "3.0.0"),}}
   {{ .package(url: "https://github.com/vapor/auth.git", from: "2.0.0"),}}
   {{ ],}}
   {{ targets: [}}
   {{ .target(name: "App", dependencies: ["Authentication", "FluentPostgreSQL", "Vapor"]),}}
   {{ .target(name: "Run", dependencies: ["App"]),}}
   {{ .testTarget(name: "AppTests", dependencies: ["App"])}}
   {{ ]}}
   )

3. Run swift package resolve

Expected outcome:

• Error produced showing could not be satisfied

• Ideally says 3.0.0 does not exist

Actual outcome:
SPM gets stuck in an infinite loop

[weissi]

@aciidb0mb3r/ @neonichu pretty sure this is fixed with pubgrub?