Add --use flag to install

Sources/Swiftly/Install.swift

@@ -43,6 +43,9 @@ struct Install: SwiftlyCommand {
     ))
     var version: String
 
+    @Flag(name: .shortAndLong, help: "Mark the newly installed toolchain as in-use.")
+    var use: Bool = false
+
     @Option(help: ArgumentHelp(
         "A GitHub authentiation token to use for any GitHub API requests.",
         discussion: """
@@ -56,21 +59,22 @@ struct Install: SwiftlyCommand {
     public var httpClient = SwiftlyHTTPClient()
 
     private enum CodingKeys: String, CodingKey {
-        case version, token
+        case version, token, use
     }
 
     mutating func run() async throws {
         let selector = try ToolchainSelector(parsing: self.version)
         self.httpClient.githubToken = self.token
         let toolchainVersion = try await self.resolve(selector: selector)
         var config = try Config.load()
-        try await Self.execute(version: toolchainVersion, &config, self.httpClient)
+        try await Self.execute(version: toolchainVersion, &config, self.httpClient, useInstalledToolchain: self.use)
     }
 
     internal static func execute(
         version: ToolchainVersion,
         _ config: inout Config,
-        _ httpClient: SwiftlyHTTPClient
+        _ httpClient: SwiftlyHTTPClient,
+        useInstalledToolchain: Bool
     ) async throws {
         guard !config.installedToolchains.contains(version) else {
             SwiftlyCore.print("\(version) is already installed, exiting.")
@@ -168,8 +172,9 @@ struct Install: SwiftlyCommand {
         config.installedToolchains.insert(version)
         try config.save()
 
-        // If this is the first installed toolchain, mark it as in-use.
-        if config.inUse == nil {
+        // If this is the first installed toolchain, mark it as in-use regardless of whether the
+        // --use argument was provided.
+        if useInstalledToolchain || config.inUse == nil {
             try await Use.execute(version, &config)
         }
 

Sources/Swiftly/Update.swift

@@ -100,11 +100,12 @@ struct Update: SwiftlyCommand {
             }
         }
 
-        try await Install.execute(version: newToolchain, &config, self.httpClient)
-
-        if config.inUse == parameters.oldToolchain {
-            try await Use.execute(newToolchain, &config)
-        }
+        try await Install.execute(
+            version: newToolchain,
+            &config,
+            self.httpClient,
+            useInstalledToolchain: config.inUse == parameters.oldToolchain
+        )
 
         try await Uninstall.execute(parameters.oldToolchain, &config)
         SwiftlyCore.print("Successfully updated \(parameters.oldToolchain) ⟶ \(newToolchain)")

Tests/SwiftlyTests/InstallTests.swift

@@ -255,4 +255,16 @@ final class InstallTests: SwiftlyTests {
             try await self.validateInUse(expected: ToolchainVersion(major: 5, minor: 7, patch: 0))
         }
     }
+
+    /// Verify that the installed toolchain will be marked as in-use if the --use flag is specified.
+    func testInstallUseFlag() async throws {
+        try await self.withTestHome {
+            try await self.installMockedToolchain(toolchain: Self.oldStable)
+            var use = try self.parseCommand(Use.self, ["use", Self.oldStable.name])
+            try await use.run()
+            try await validateInUse(expected: Self.oldStable)
+            try await self.installMockedToolchain(selector: Self.newStable.name, args: ["--use"])
+            try await self.validateInUse(expected: Self.newStable)
+        }
+    }
 }

Tests/SwiftlyTests/SwiftlyTests.swift

@@ -172,8 +172,8 @@ class SwiftlyTests: XCTestCase {
     /// in its bin directory.
     ///
     /// When executed, the mocked executables will simply print the toolchain version and return.
-    func installMockedToolchain(selector: String, executables: [String]? = nil) async throws {
-        var install = try self.parseCommand(Install.self, ["install", "\(selector)"])
+    func installMockedToolchain(selector: String, args: [String] = [], executables: [String]? = nil) async throws {
+        var install = try self.parseCommand(Install.self, ["install", "\(selector)"] + args)
         install.httpClient = SwiftlyHTTPClient(toolchainDownloader: MockToolchainDownloader(executables: executables))
         try await install.run()
     }