Let users choose where Steam is installed

app/Sources/NotProtonApp/Model/SteamRepair.swift

@@ -178,6 +178,16 @@ enum SteamRepair {
     static func replace(_ app: URL, with staged: URL) throws {
         let files = FileManager.default
         try WriteRefused.catching(app) {
+            // The swap below cannot cross drives, so Steam on an external drive gets a copy beside it first.
+            var staged = staged
+            let folder = app.deletingLastPathComponent()
+            if volume(of: staged) != volume(of: folder) {
+                let copy = folder.appending(path: ".\(app.lastPathComponent).\(UUID().uuidString)")
+                try files.copyItem(at: staged, to: copy)
+                staged = copy
+            }
+            defer { try? files.removeItem(at: staged) }
+
             guard files.fileExists(atPath: app.path(percentEncoded: false)) else {
                 try files.moveItem(at: staged, to: app)
                 return
@@ -186,6 +196,10 @@ enum SteamRepair {
         }
     }
 
+    private static func volume(of url: URL) -> URL? {
+        try? url.resourceValues(forKeys: [.volumeURLKey]).volume
+    }
+
     static func clearInsert(at plist: URL) throws -> Bool {
         guard var dict = SteamBundle.readInfoPlist(at: plist),
               var environment = dict[SteamBundle.environmentKey] as? [String: Any]

app/Sources/NotProtonApp/Support/SupportPaths.swift

@@ -66,7 +66,13 @@ enum SupportPaths {
     static let bridgeCacheFolder = "bridge"
 
     enum Steam {
-        static var app: URL { URL(filePath: "/Applications/Steam.app") }
+        static let defaultApp = URL(filePath: "/Applications/Steam.app")
+        // Set from the Status page when Steam lives somewhere else, like an external drive.
+        static let appPathKey = "steamAppPath"
+
+        static var app: URL {
+            UserDefaults.standard.string(forKey: appPathKey).map { URL(filePath: $0) } ?? defaultApp
+        }
         static var infoPlist: URL { infoPlist(inBundle: app) }
         static var executable: URL { app.appending(path: "Contents/MacOS/steam_osx") }
         static var deployedDylib: URL { deployedDylib(inBundle: app) }

app/Sources/NotProtonApp/SystemStatus.swift

@@ -284,6 +284,49 @@ final class SystemStatus {
         await refresh()
     }
 
+    func chooseSteam() async {
+        let current = SupportPaths.Steam.app
+        let panel = NSOpenPanel()
+        panel.canChooseFiles = true
+        panel.canChooseDirectories = false
+        panel.allowsMultipleSelection = false
+        panel.allowedContentTypes = [.application]
+        panel.prompt = "Choose"
+        panel.message = "Select your copy of Steam."
+        panel.directoryURL = current.deletingLastPathComponent()
+
+        guard panel.runModal() == .OK, let url = panel.url else { return }
+        // The panel returns bundles as directories, with a trailing slash.
+        let picked = URL(filePath: url.path)
+
+        clearFailure()
+        outcome = nil
+
+        guard Bundle(url: picked)?.bundleIdentifier == SteamRepair.valveIdentifier else {
+            setFailure("\(picked.lastPathComponent) is not Steam.")
+            AppLog.note("steam choice refused: \(picked.path(percentEncoded: false))")
+            return
+        }
+        guard !CrossOverSource.same(picked, current) else { return }
+
+        // Moving on would leave the old copy patched, out of reach of Repair and Remove Everything.
+        let deployed = SupportPaths.Steam.deployedDylib(inBundle: current).path(percentEncoded: false)
+        if let insert = SteamBundle.currentInsert(), insert.split(separator: ":").contains(Substring(deployed)) {
+            setFailure("NotProton is installed in \(current.path(percentEncoded: false)). "
+                + "Use Repair Steam to remove it before choosing another copy of Steam.")
+            AppLog.note("steam choice refused, still patched: \(current.path(percentEncoded: false))")
+            return
+        }
+
+        if CrossOverSource.same(picked, SupportPaths.Steam.defaultApp) {
+            UserDefaults.standard.removeObject(forKey: SupportPaths.Steam.appPathKey)
+        } else {
+            UserDefaults.standard.set(picked.path(percentEncoded: false), forKey: SupportPaths.Steam.appPathKey)
+        }
+        AppLog.note("steam chosen: \(picked.path(percentEncoded: false))")
+        await refresh()
+    }
+
     private func highlight(_ row: CrossOverRow) {
         AccessibilityNotification.Announcement("\(row.title) is already listed.").post()
         highlightReset?.cancel()

app/Sources/NotProtonApp/Views/StatusView.swift

@@ -322,6 +322,15 @@ struct StatusView: View {
             }
 
             Section("Steam") {
+                StatusRow(
+                    title: "Location",
+                    value: SupportPaths.Steam.app.path(percentEncoded: false),
+                    action: StatusAction(
+                        label: "Choose\u{2026}",
+                        help: "Use a copy of Steam from another folder or drive.",
+                        isEnabled: status.isIdle
+                    ) { Task { await status.chooseSteam() } }
+                )
                 steamRow(snapshot.steam, payload: snapshot.payload)
                 if snapshot.steamRunning {
                     StatusRow(