Do not realpath the project root of a SwiftPMBuildSystem

If you have a package located at `/pkg` and a symlink at `/symlink` and you open `/symlink` as a workspace, the SwiftPMBuildSystem’s project root would be `/pkg`. This would mean that it also only knew about build settings for files in `/pkg`, not in `/symlink`. Thus, whenever we were opening a file in `/symlink` we would create an implicit workspace to handle it (but which ended up having a project root at `/symlink` again) – or something close to this.

We shouldn’t need to realpath here. If you open `/symlink`, we should view `/symlink` as the project root of your workspace.

(cherry picked from commit 8617b8b)

Author: ahoppen

Sources/BuildSystemIntegration/SwiftPMBuildSystem.swift

@@ -169,9 +169,7 @@ package actor SwiftPMBuildSystem: BuiltInBuildSystem {
   private var targetDependencies: [BuildTargetIdentifier: Set<BuildTargetIdentifier>] = [:]
 
   static package func projectRoot(for path: URL, options: SourceKitLSPOptions) -> URL? {
-    guard var path = orLog("Getting realpath for project root", { try path.realpath }) else {
-      return nil
-    }
+    var path = path
     while true {
       let packagePath = path.appendingPathComponent("Package.swift")
       if (try? String(contentsOf: packagePath, encoding: .utf8))?.contains("PackageDescription") ?? false {

Tests/BuildSystemIntegrationTests/SwiftPMBuildSystemTests.swift

@@ -806,28 +806,21 @@ final class SwiftPMBuildSystemTests: XCTestCase {
           fallbackAfterTimeout: false
         )
       ).compilerArguments
-      let argumentsFromReal = try await unwrap(
-        buildSystemManager.buildSettingsInferredFromMainFile(
-          for: DocumentURI(aswiftReal),
-          language: .swift,
-          fallbackAfterTimeout: false
-        )
-      ).compilerArguments
 
-      // The arguments retrieved from the symlink and the real document should be the same, except that both should
-      // contain they file the build settings were created.
-      // FIXME: Or should the build settings always reference the main file?
-      XCTAssertEqual(
-        try argumentsFromSymlink.filter { try $0 != aswiftSymlink.filePath && $0 != aswiftReal.filePath },
-        try argumentsFromReal.filter { try $0 != aswiftSymlink.filePath && $0 != aswiftReal.filePath }
+      // We opened the project from a symlink. The realpath isn't part of the project and we should thus not receive
+      // build settings for it.
+      assertTrue(
+        try await unwrap(
+          buildSystemManager.buildSettingsInferredFromMainFile(
+            for: DocumentURI(aswiftReal),
+            language: .swift,
+            fallbackAfterTimeout: false
+          )
+        ).isFallback
       )
-
       assertArgumentsContain(try aswiftSymlink.filePath, arguments: argumentsFromSymlink)
       assertArgumentsDoNotContain(try aswiftReal.filePath, arguments: argumentsFromSymlink)
 
-      assertArgumentsContain(try aswiftReal.filePath, arguments: argumentsFromReal)
-      assertArgumentsDoNotContain(try aswiftSymlink.filePath, arguments: argumentsFromReal)
-
       let argsManifest = try await unwrap(
         buildSystemManager.buildSettingsInferredFromMainFile(
           for: DocumentURI(manifest),