Use {install-root}/libexec/container-plugins for plugins. (#341)

- Use a directory that's separate from user data, as user-installed
plugins have a distinct lifecycle.
- Closes #340.

Sources/APIServer/APIServer.swift

@@ -129,18 +129,28 @@ struct APIServer: AsyncParsableCommand {
     }
 
     private func initializePluginLoader(log: Logger) throws -> PluginLoader {
-        // create user-installed plugins directory if it doesn't exist
-        let pluginsURL = PluginLoader.userPluginsDir(root: Self.appRoot)
-        try FileManager.default.createDirectory(at: pluginsURL, withIntermediateDirectories: true)
+        let installRoot = CommandLine.executablePathUrl
+            .deletingLastPathComponent()
+            .appendingPathComponent("..")
+            .standardized
+        let pluginsURL = PluginLoader.userPluginsDir(root: installRoot)
+        var directoryExists: ObjCBool = false
+        _ = FileManager.default.fileExists(atPath: pluginsURL.path, isDirectory: &directoryExists)
+        let userPluginsURL = directoryExists.boolValue ? pluginsURL : nil
 
         // plugins built into the application installed as a macOS app bundle
         let appBundlePluginsURL = Bundle.main.resourceURL?.appending(path: "plugins")
 
         // plugins built into the application installed as a Unix-like application
-        let installRootPluginsURL = CommandLine.executableDirectoryUrl.appendingPathComponent("../libexec/container/plugins")
+        let installRootPluginsURL =
+            installRoot
+            .appendingPathComponent("libexec")
+            .appendingPathComponent("container")
+            .appendingPathComponent("plugins")
+            .standardized
 
         let pluginDirectories = [
-            pluginsURL,
+            userPluginsURL,
             appBundlePluginsURL,
             installRootPluginsURL,
         ].compactMap { $0 }
@@ -150,6 +160,7 @@ struct APIServer: AsyncParsableCommand {
             AppBundlePluginFactory(),
         ]
 
+        log.info("PLUGINS: \(pluginDirectories)")
         let statePath = PluginLoader.defaultPluginResourcePath(root: Self.appRoot)
         try FileManager.default.createDirectory(at: statePath, withIntermediateDirectories: true)
         return PluginLoader(pluginDirectories: pluginDirectories, pluginFactories: pluginFactories, defaultResourcePath: statePath, log: log)

Sources/CLI/Application.swift

@@ -94,12 +94,32 @@ struct Application: AsyncParsableCommand {
     }()
 
     static let pluginLoader: PluginLoader = {
-        // create user-installed plugins directory if it doesn't exist
-        let pluginsURL = PluginLoader.userPluginsDir(root: Self.appRoot)
-        try! FileManager.default.createDirectory(at: pluginsURL, withIntermediateDirectories: true)
+        let installRoot = CommandLine.executablePathUrl
+            .deletingLastPathComponent()
+            .appendingPathComponent("..")
+            .standardized
+        let pluginsURL = PluginLoader.userPluginsDir(root: installRoot)
+        var directoryExists: ObjCBool = false
+        _ = FileManager.default.fileExists(atPath: pluginsURL.path, isDirectory: &directoryExists)
+        let userPluginsURL = directoryExists.boolValue ? pluginsURL : nil
+
+        // plugins built into the application installed as a macOS app bundle
+        let appBundlePluginsURL = Bundle.main.resourceURL?.appending(path: "plugins")
+
+        // plugins built into the application installed as a Unix-like application
+        let installRootPluginsURL =
+            installRoot
+            .appendingPathComponent("libexec")
+            .appendingPathComponent("container")
+            .appendingPathComponent("plugins")
+            .standardized
+
         let pluginDirectories = [
-            pluginsURL
-        ]
+            userPluginsURL,
+            appBundlePluginsURL,
+            installRootPluginsURL,
+        ].compactMap { $0 }
+
         let pluginFactories = [
             DefaultPluginFactory()
         ]

Sources/ContainerPlugin/CommandLine+Executable.swift

@@ -17,10 +17,20 @@
 import Foundation
 
 extension CommandLine {
-    public static var executableDirectoryUrl: URL {
-        let executablePath = Self.arguments[0]
-        let executableUrl = URL(filePath: executablePath)
-        let executableDirectoryUrl = executableUrl.deletingLastPathComponent()
-        return executableDirectoryUrl.standardized
+    public static var executablePathUrl: URL {
+        /// _NSGetExecutablePath with a zero-length buffer returns the needed buffer length
+        var bufferSize: Int32 = 0
+        var buffer = [CChar](repeating: 0, count: Int(bufferSize))
+        _ = _NSGetExecutablePath(&buffer, &bufferSize)
+
+        /// Create the buffer and get the path
+        buffer = [CChar](repeating: 0, count: Int(bufferSize))
+        guard _NSGetExecutablePath(&buffer, &bufferSize) == 0 else {
+            fatalError("UNEXPECTED: failed to get executable path")
+        }
+
+        /// Return the path with the executable file component removed the last component and
+        let executablePath = String(cString: &buffer)
+        return URL(filePath: executablePath)
     }
 }

Sources/ContainerPlugin/PluginLoader.swift

@@ -44,7 +44,10 @@ public struct PluginLoader: Sendable {
     }
 
     static public func userPluginsDir(root: URL) -> URL {
-        root.appending(path: "user-plugins")
+        root
+            .appending(path: "libexec")
+            .appending(path: "container-plugins")
+            .resolvingSymlinksInPath()
     }
 }
 

Tests/ContainerPluginTests/CommandLine+ExecutableTest.swift

@@ -0,0 +1,27 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2025 Apple Inc. and the container project authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import Foundation
+import Testing
+
+@testable import ContainerPlugin
+
+struct CommandLineExecutableTest {
+    @Test
+    func testCLIPluginConfigLoad() async throws {
+        #expect(CommandLine.executablePathUrl.lastPathComponent == "swiftpm-testing-helper")
+    }
+}