fix a bug in resolving registry dependencies with alternative manifest versions (#4198)

motivation: fix an existing issue with registry dependencies that can lead to resolution failure

changes:
* improve the placeholder manifest lookup of registry based dependencies that have alternative manifests
* add test

Author: tomerd

Sources/Workspace/RegistryPackageContainer.swift

@@ -173,8 +173,20 @@ public class RegistryPackageContainer: PackageContainer {
                                 return completion(.failure(error))
                             case .success(let manifestContent):
                                 do {
+                                    // find the fake manifest so we can replace it with the real manifest content
+                                    guard let placeholderManifestFileName = try fileSystem.getDirectoryContents(.root).first(where: { file in
+                                        if file == Manifest.basename + "@swift-\(preferredToolsVersion).swift" {
+                                            return true
+                                        } else if preferredToolsVersion.patch == 0, file == Manifest.basename + "@swift-\(preferredToolsVersion.major).\(preferredToolsVersion.minor).swift" {
+                                            return true
+                                        } else {
+                                            return false
+                                        }
+                                    }) else {
+                                        throw StringError("failed locating placeholder manifest for \(preferredToolsVersion)")
+                                    }
                                     // replace the fake manifest with the real manifest content
-                                    let manifestPath = AbsolutePath.root.appending(component: Manifest.basename + "@swift-\(preferredToolsVersion).swift")
+                                    let manifestPath = AbsolutePath.root.appending(component: placeholderManifestFileName)
                                     try fileSystem.removeFileTree(manifestPath)
                                     try fileSystem.writeFileContents(manifestPath, string: manifestContent)
                                     // finally, load the manifest

Tests/WorkspaceTests/RegistryPackageContainerTests.swift

@@ -208,6 +208,8 @@ class RegistryPackageContainerTests: XCTestCase {
         let packageVersion = Version("1.0.0")
         let packagePath = AbsolutePath.root
 
+        let v5_3_3 = ToolsVersion(string: "5.3.3")!
+
         func createProvider(_ toolsVersion: ToolsVersion) throws -> PackageContainerProvider {
             let registryClient = try makeRegistryClient(
                 packageIdentity: packageIdentity,
@@ -222,6 +224,7 @@ class RegistryPackageContainerTests: XCTestCase {
                                 "Content-Version": "1",
                                 "Content-Type": "text/x-swift",
                                 "Link": """
+                                \(self.manifestLink(packageIdentity, v5_3_3)),
                                 \(self.manifestLink(packageIdentity, .v5_4)),
                                 \(self.manifestLink(packageIdentity, .v5_5))
                                 """
@@ -279,6 +282,14 @@ class RegistryPackageContainerTests: XCTestCase {
             XCTAssertEqual(manifest.toolsVersion, .v5_3)
         }
 
+        do {
+            let provider = try createProvider(v5_3_3) // the version of the alternate
+            let ref = PackageReference.registry(identity: packageIdentity)
+            let container = try provider.getContainer(for: ref, skipUpdate: false) as! RegistryPackageContainer
+            let manifest = try container.loadManifest(version: packageVersion)
+            XCTAssertEqual(manifest.toolsVersion, v5_3_3)
+        }
+
         do {
             let provider = try createProvider(.v5_4) // the version of the alternate
             let ref = PackageReference.registry(identity: packageIdentity)
@@ -453,7 +464,8 @@ class RegistryPackageContainerTests: XCTestCase {
         guard let (scope, name) = identity.scopeAndName else {
             preconditionFailure("invalid identity")
         }
-        return "<http://localhost/\(scope)/\(name)/\(version)/\(Manifest.filename)?swift-version=\(version)>; rel=\"alternate\"; filename=\"Package@swift-\(version).swift\"; swift-tools-version=\"\(version)\""
+        let versionString = version.patch == 0 ? "\(version.major).\(version.minor)" : version.description
+        return "<http://localhost/\(scope)/\(name)/\(version)/\(Manifest.filename)?swift-version=\(version)>; rel=\"alternate\"; filename=\"\(Manifest.basename)@swift-\(versionString).swift\"; swift-tools-version=\"\(version)\""
     }
 }