[SR-15616] Inconsistent validation of local package path in SwiftPM

[stackotter]

Previous ID	SR-15616
Radar	None
Original Reporter	@stackotter
Type	Bug

Environment

Xcode Version 13.2 (13C90)

swift-driver version: 1.26.21 Apple Swift version 5.5.2 (swiftlang-1300.0.47.5 clang-1300.0.29.30)

Target: x86_64-apple-macosx12.0

Additional Detail from JIRA

Votes	0
Component/s	Package Manager
Labels	Bug
Assignee	None
Priority	Medium

md5: bb0eb88610d50cf42613003444078194

Issue Description:

I am developing an app which is a Swift package. Building it using swift build works completely fine. However, when I include it as a dependency in another package, building that package fails with the following error:

invalidManifestFormat("'./Sources/Core' is not a valid path for path-based dependencies; use relative or absolute path instead.", diagnosticFile: nil) in https://github.com/stackotter/delta-client.

The path that is causing the error is valid when building the delta-client package, but not when delta-client is a dependency.

Here is an example Package.swift that results in the aforementioned error:

// swift-tools-version:5.5

import PackageDescription

let package = Package(
  name: "BugReproducer",
  dependencies: [
    .package(name: "DeltaClient", url: "https://github.com/stackotter/delta-client", .branch("refactor-rendering")),
  ],
  targets: [
    .executableTarget(
      name: "BugReproducer",
      dependencies: [
        .product(name: "StaticShim", package: "DeltaClient")
      ]),
  ]
)

[stackotter]

Removing the ./ does stop the error, but the inconsistency is a bit odd.