Remove swiftly from the path during proxying

Sources/SwiftlyCore/Platform.swift

@@ -139,19 +139,25 @@ extension Platform {
     }
 
 #if os(macOS) || os(Linux)
-    internal func proxyEnv(_ toolchain: ToolchainVersion) throws -> [String: String] {
+    internal func proxyEnv(env: [String: String], toolchain: ToolchainVersion) throws -> [String: String] {
+        var newEnv = env
+
         let tcPath = self.findToolchainLocation(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)"
-        }
-        newEnv["PATH"] = newPath
+        pathComponents.removeAll(where: { $0 == tcPath.path })
+        pathComponents = [tcPath.path] + pathComponents
+
+        // Remove swiftly bin directory from the PATH entirely
+        let swiftlyBinDir = self.swiftlyBinDir
+        pathComponents.removeAll(where: { $0 == swiftlyBinDir.path })
+
+        newEnv["PATH"] = String(pathComponents.joined(by: ":"))
 
         return newEnv
     }
@@ -162,11 +168,22 @@ extension Platform {
     /// the exit code and program information.
     ///
     public func proxy(_ toolchain: ToolchainVersion, _ command: String, _ arguments: [String], _ env: [String: String] = [:]) async throws {
-        var newEnv = try self.proxyEnv(toolchain)
+        var newEnv = try self.proxyEnv(env: ProcessInfo.processInfo.environment, toolchain: toolchain)
+
+        let tcPath = self.findToolchainLocation(toolchain).appendingPathComponent("usr/bin")
+
+        let commandTcPath = tcPath.appendingPathComponent(command)
+        let commandToRun = if FileManager.default.fileExists(atPath: commandTcPath.path) {
+            commandTcPath.path
+        } else {
+            command
+        }
+
         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.
@@ -175,7 +192,16 @@ extension Platform {
     /// the exit code and program information.
     ///
     public func proxyOutput(_ toolchain: ToolchainVersion, _ command: String, _ arguments: [String]) async throws -> String? {
-        try await self.runProgramOutput(command, arguments, env: self.proxyEnv(toolchain))
+        let tcPath = self.findToolchainLocation(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(env: ProcessInfo.processInfo.environment, toolchain: toolchain))
     }
 
     /// Run a program.

Tests/SwiftlyTests/PlatformTests.swift

@@ -73,4 +73,34 @@ final class PlatformTests: SwiftlyTests {
             XCTAssertEqual(0, toolchains.count)
         }
     }
+
+#if os(macOS) || os(Linux)
+    func testProxyEnv() async throws {
+        try await self.rollbackLocalChanges {
+            var (mockedToolchainFile, version) = try await self.mockToolchainDownload(version: SwiftlyTests.newStable.name)
+            try Swiftly.currentPlatform.install(from: mockedToolchainFile, version: version, verbose: true)
+
+            for path in [
+                "/a/b/c:SWIFTLY_BIN_DIR:/d/e/f",
+                "SWIFTLY_BIN_DIR:/abcde",
+                "/defgh:SWIFTLY_BIN_DIR",
+                "/xyzabc:/1/3/4",
+                "",
+            ] {
+                // GIVEN: a PATH that may contain the swiftly bin directory
+                let env = ["PATH": path.replacing("SWIFTLY_BIN_DIR", with: Swiftly.currentPlatform.swiftlyBinDir.path)]
+
+                // WHEN: proxying to an installed toolchain
+                let newEnv = try Swiftly.currentPlatform.proxyEnv(env: env, toolchain: SwiftlyTests.newStable)
+
+                // THEN: the toolchain's bin directory is added to the beginning of the PATH
+                XCTAssert(newEnv["PATH"]!.hasPrefix(Swiftly.currentPlatform.findToolchainLocation(SwiftlyTests.newStable).appendingPathComponent("usr/bin").path))
+
+                // AND: the swiftly bin directory is removed from the PATH
+                XCTAssert(!newEnv["PATH"]!.contains(Swiftly.currentPlatform.swiftlyBinDir.path))
+                XCTAssert(!newEnv["PATH"]!.contains(Swiftly.currentPlatform.swiftlyBinDir.path))
+            }
+        }
+    }
+#endif
 }