Fix watcher crashing in package subdirectories

.vscode/tasks.json

@@ -33,6 +33,11 @@
       "type": "shell",
       "command": "swift build && cd TestApp && ../.build/debug/carton dev --product TestApp"
     },
+    {
+      "label": "build and run dev in subdirectory",
+      "type": "shell",
+      "command": "swift build && cd TestApp/Sources/TestApp && ../../../.build/debug/carton dev --product TestApp"
+    },
     {
       "label": "build and run test",
       "type": "shell",

Sources/CartonHelpers/ProcessRunner.swift

@@ -59,7 +59,11 @@ public final class ProcessRunner {
         }, receiveCompletion: {
           switch $0 {
           case .finished:
-            terminal.write("\nProcess completed successfully\n", inColor: .green, bold: false)
+            terminal.write(
+              "\n`\(AbsolutePath(arguments[0]).basename)` process finished successfully\n",
+              inColor: .green,
+              bold: false
+            )
           case let .failure(error):
             let errorString = String(describing: error)
             if errorString.isEmpty {

Sources/SwiftToolchain/Toolchain.swift

@@ -44,7 +44,10 @@ enum ToolchainError: Error, CustomStringConvertible {
     case .failedToBuildTestBundle:
       return "Failed to build the test bundle"
     case .missingPackage:
-      return "No package found"
+      return """
+      The `Package.swift` manifest file could not be found. Please navigate to a directory that \
+      contains `Package.swift` and restart.
+      """
     }
   }
 }
@@ -118,8 +121,27 @@ public final class Toolchain {
     }
   }
 
+  private func inferManifestDirectory() throws -> AbsolutePath {
+    guard package != nil, var cwd = fileSystem.currentWorkingDirectory else {
+      throw ToolchainError.missingPackage
+    }
+
+    repeat {
+      guard !fileSystem.isFile(cwd.appending(component: "Package.swift")) else {
+        return cwd
+      }
+
+      // `parentDirectory` just returns `self` if it's `root`
+      cwd = cwd.parentDirectory
+    } while !cwd.isRoot
+
+    throw ToolchainError.missingPackage
+  }
+
   public func inferSourcesPaths() throws -> [AbsolutePath] {
-    let package = try Package(with: swiftPath, terminal)
+    guard let package = package else {
+      throw ToolchainError.missingPackage
+    }
 
     let targetPaths = package.targets.compactMap { target -> String? in
       guard let path = target.path else {
@@ -133,8 +155,10 @@ public final class Toolchain {
       return path
     }
 
+    let manifestDirectory = try inferManifestDirectory()
+
     return try targetPaths.compactMap {
-      try fileSystem.currentWorkingDirectory?.appending(RelativePath(validating: $0))
+      try manifestDirectory.appending(RelativePath(validating: $0))
     }
   }
 

Sources/carton/Combine/Watcher.swift

@@ -28,6 +28,8 @@ final class Watcher {
   init(_ paths: [AbsolutePath]) throws {
     publisher = subject.eraseToAnyPublisher()
 
+    guard !paths.isEmpty else { return }
+
     fsWatch = FSWatch(paths: paths, latency: 0.1) { [weak self] in
       self?.subject.send($0)
     }

Sources/carton/Helpers/FileSystem.swift

@@ -16,11 +16,18 @@ import Foundation
 import TSCBasic
 
 extension FileSystem {
-  func traverseRecursively(_ root: AbsolutePath) throws -> [AbsolutePath] {
-    precondition(isDirectory(root))
-    var result = [root]
+  func traverseRecursively(_ traversalRoot: AbsolutePath) throws -> [AbsolutePath] {
+    guard exists(traversalRoot, followSymlink: true) else {
+      return []
+    }
+
+    var result = [traversalRoot]
+
+    guard isDirectory(traversalRoot) else {
+      return result
+    }
 
-    var pathsToTraverse = [root]
+    var pathsToTraverse = result
     while let currentDirectory = pathsToTraverse.popLast() {
       let directoryContents = try getDirectoryContents(currentDirectory)
         .map(currentDirectory.appending)