Remove swiftly from the path during proxying

Sources/Swiftly/Run.swift

@@ -105,6 +105,9 @@ struct Run: SwiftlyCommand {
 
             try await Swiftly.currentPlatform.proxy(ctx, toolchain, command[0], [String](command[1...]))
         } catch let terminated as RunProgramError {
+            if ctx.mockedHomeDir != nil {
+                throw terminated
+            }
             Foundation.exit(terminated.exitCode)
         } catch {
             throw error

Sources/SwiftlyCore/Platform.swift

@@ -164,25 +164,29 @@ extension Platform {
     }
 
 #if os(macOS) || os(Linux)
-    func proxyEnv(_ ctx: SwiftlyCoreContext, _ toolchain: ToolchainVersion) throws -> [
-        String:
-            String
-    ] {
+    func proxyEnv(_ ctx: SwiftlyCoreContext, env: [String: String], toolchain: ToolchainVersion) throws -> [String: String] {
+        var newEnv = env
+
         let tcPath = self.findToolchainLocation(ctx, toolchain).appendingPathComponent("usr/bin")
         guard tcPath.fileExists() else {
             throw SwiftlyError(
                 message:
                 "Toolchain \(toolchain) could not be located. You can try `swiftly uninstall \(toolchain)` to uninstall it and then `swiftly install \(toolchain)` to install it again."
             )
         }
-        var newEnv = ProcessInfo.processInfo.environment
+
+        var pathComponents = (newEnv["PATH"] ?? "").split(separator: ":").map { String($0) }
 
         // The toolchain goes to the beginning of the PATH
-        var newPath = newEnv["PATH"] ?? ""
-        if !newPath.hasPrefix(tcPath.path + ":") {
-            newPath = "\(tcPath.path):\(newPath)"
+        if pathComponents.first ?? "" != tcPath.path {
+            pathComponents = [tcPath.path] + pathComponents
         }
-        newEnv["PATH"] = newPath
+
+        // Remove swiftly bin directory from the PATH
+        let swiftlyBinDir = self.swiftlyBinDir(ctx).path
+        pathComponents.removeAll(where: { $0 == swiftlyBinDir })
+
+        newEnv["PATH"] = String(pathComponents.joined(by: ":"))
 
         return newEnv
     }
@@ -192,27 +196,40 @@ extension Platform {
     /// In the case where the command exit with a non-zero exit code a RunProgramError is thrown with
     /// the exit code and program information.
     ///
-    public func proxy(
-        _ ctx: SwiftlyCoreContext, _ toolchain: ToolchainVersion, _ command: String,
-        _ arguments: [String], _ env: [String: String] = [:]
-    ) async throws {
-        var newEnv = try self.proxyEnv(ctx, toolchain)
+    public func proxy(_ ctx: SwiftlyCoreContext, _ toolchain: ToolchainVersion, _ command: String, _ arguments: [String], _ env: [String: String] = [:]) async throws {
+        let tcPath = self.findToolchainLocation(ctx, toolchain).appendingPathComponent("usr/bin")
+
+        let commandTcPath = tcPath.appendingPathComponent(command)
+        let commandToRun = if FileManager.default.fileExists(atPath: commandTcPath.path) {
+            commandTcPath.path
+        } else {
+            command
+        }
+
+        var newEnv = try self.proxyEnv(ctx, env: ProcessInfo.processInfo.environment, toolchain: toolchain)
         for (key, value) in env {
             newEnv[key] = value
         }
-        try self.runProgram([command] + arguments, env: newEnv)
+
+        try self.runProgram([commandToRun] + arguments, env: newEnv)
     }
 
     /// Proxy the invocation of the provided command to the chosen toolchain and capture the output.
     ///
     /// In the case where the command exit with a non-zero exit code a RunProgramError is thrown with
     /// the exit code and program information.
     ///
-    public func proxyOutput(
-        _ ctx: SwiftlyCoreContext, _ toolchain: ToolchainVersion, _ command: String,
-        _ arguments: [String]
-    ) async throws -> String? {
-        try await self.runProgramOutput(command, arguments, env: self.proxyEnv(ctx, toolchain))
+    public func proxyOutput(_ ctx: SwiftlyCoreContext, _ toolchain: ToolchainVersion, _ command: String, _ arguments: [String]) async throws -> String? {
+        let tcPath = self.findToolchainLocation(ctx, toolchain).appendingPathComponent("usr/bin")
+
+        let commandTcPath = tcPath.appendingPathComponent(command)
+        let commandToRun = if FileManager.default.fileExists(atPath: commandTcPath.path) {
+            commandTcPath.path
+        } else {
+            command
+        }
+
+        return try await self.runProgramOutput(commandToRun, arguments, env: self.proxyEnv(ctx, env: ProcessInfo.processInfo.environment, toolchain: toolchain))
     }
 
     /// Run a program.

Tests/SwiftlyTests/PlatformTests.swift

@@ -85,4 +85,30 @@ import Testing
         toolchains = try FileManager.default.contentsOfDirectory(at: Swiftly.currentPlatform.swiftlyToolchainsDir(SwiftlyTests.ctx), includingPropertiesForKeys: nil)
         #expect(0 == toolchains.count)
     }
+
+#if os(macOS) || os(Linux)
+    @Test(
+        .mockHomeToolchains(),
+        arguments: [
+            "/a/b/c:SWIFTLY_BIN_DIR:/d/e/f",
+            "SWIFTLY_BIN_DIR:/abcde",
+            "/defgh:SWIFTLY_BIN_DIR",
+            "/xyzabc:/1/3/4",
+            "",
+        ]
+    ) func proxyEnv(_ path: String) async throws {
+        // GIVEN: a PATH that may contain the swiftly bin directory
+        let env = ["PATH": path.replacing("SWIFTLY_BIN_DIR", with: Swiftly.currentPlatform.swiftlyBinDir(SwiftlyTests.ctx).path)]
+
+        // WHEN: proxying to an installed toolchain
+        let newEnv = try Swiftly.currentPlatform.proxyEnv(SwiftlyTests.ctx, env: env, toolchain: .newStable)
+
+        // THEN: the toolchain's bin directory is added to the beginning of the PATH
+        #expect(newEnv["PATH"]!.hasPrefix(Swiftly.currentPlatform.findToolchainLocation(SwiftlyTests.ctx, .newStable).appendingPathComponent("usr/bin").path))
+
+        // AND: the swiftly bin directory is removed from the PATH
+        #expect(!newEnv["PATH"]!.contains(Swiftly.currentPlatform.swiftlyBinDir(SwiftlyTests.ctx).path))
+        #expect(!newEnv["PATH"]!.contains(Swiftly.currentPlatform.swiftlyBinDir(SwiftlyTests.ctx).path))
+    }
+#endif
 }