Add support for redirecting stderr to stdout.

Author: sergiocampama

Sources/TSCBasic/Process.swift

@@ -129,10 +129,20 @@ public final class Process: ObjectIdentifierProtocol {
     public enum OutputRedirection {
         /// Do not redirect the output
         case none
-        /// Collect stdout and stderr output and provide it back via ProcessResult object
-        case collect
-        /// Stream stdout and stderr via the corresponding closures
-        case stream(stdout: OutputClosure, stderr: OutputClosure)
+        /// Collect stdout and stderr output and provide it back via ProcessResult object. If redirectStderr is true,
+        /// stderr be redirected to stdout.
+        case collect(redirectStderr: Bool)
+        /// Stream stdout and stderr via the corresponding closures. If redirectStderr is true, stderr be redirected to
+        /// stdout.
+        case stream(stdout: OutputClosure, stderr: OutputClosure, redirectStderr: Bool)
+
+        /// Default collect OutputRedirection that defaults to not redirect stderr. Provided for API compatibility.
+        public static let collect: OutputRedirection = .collect(redirectStderr: false)
+
+        /// Default stream OutputRedirection that defaults to not redirect stderr. Provided for API compatibility.
+        public static func stream(stdout: @escaping OutputClosure, stderr: @escaping OutputClosure) -> Self {
+            return .stream(stdout: stdout, stderr: stderr, redirectStderr: false)
+        }
 
         public var redirectsOutput: Bool {
             switch self {
@@ -145,12 +155,23 @@ public final class Process: ObjectIdentifierProtocol {
 
         public var outputClosures: (stdoutClosure: OutputClosure, stderrClosure: OutputClosure)? {
             switch self {
-            case .stream(let stdoutClosure, let stderrClosure):
+            case let .stream(stdoutClosure, stderrClosure, _):
                 return (stdoutClosure: stdoutClosure, stderrClosure: stderrClosure)
             case .collect, .none:
                 return nil
             }
         }
+
+        public var redirectStderr: Bool {
+            switch self {
+            case let .collect(redirectStderr):
+                return redirectStderr
+            case let .stream(_, _, redirectStderr):
+                return redirectStderr
+            default:
+                return false
+            }
+        }
     }
 
     /// Typealias for process id type.
@@ -433,19 +454,30 @@ public final class Process: ObjectIdentifierProtocol {
         // Open /dev/null as stdin.
         posix_spawn_file_actions_addopen(&fileActions, 0, devNull, O_RDONLY, 0)
 
-        var outputPipe: [Int32] = [0, 0]
-        var stderrPipe: [Int32] = [0, 0]
+        var outputPipe: [Int32] = [-1, -1]
+        var stderrPipe: [Int32] = [-1, -1]
         if outputRedirection.redirectsOutput {
-            // Open the pipes.
+            // Open the pipe.
             try open(pipe: &outputPipe)
-            try open(pipe: &stderrPipe)
-            // Open the write end of the pipe as stdout and stderr, if desired.
+
+            // Open the write end of the pipe.
             posix_spawn_file_actions_adddup2(&fileActions, outputPipe[1], 1)
-            posix_spawn_file_actions_adddup2(&fileActions, stderrPipe[1], 2)
+
             // Close the other ends of the pipe.
-            for pipe in [outputPipe, stderrPipe] {
-                posix_spawn_file_actions_addclose(&fileActions, pipe[0])
-                posix_spawn_file_actions_addclose(&fileActions, pipe[1])
+            posix_spawn_file_actions_addclose(&fileActions, outputPipe[0])
+            posix_spawn_file_actions_addclose(&fileActions, outputPipe[1])
+
+            if outputRedirection.redirectStderr {
+                // If merged was requested, send stderr to stdout.
+                posix_spawn_file_actions_adddup2(&fileActions, 1, 2)
+            } else {
+                // If no redirect was requested, open the pipe for stderr.
+                try open(pipe: &stderrPipe)
+                posix_spawn_file_actions_adddup2(&fileActions, stderrPipe[1], 2)
+
+                // Close the other ends of the pipe.
+                posix_spawn_file_actions_addclose(&fileActions, stderrPipe[0])
+                posix_spawn_file_actions_addclose(&fileActions, stderrPipe[1])
             }
         } else {
             posix_spawn_file_actions_adddup2(&fileActions, 1, 1)
@@ -475,17 +507,20 @@ public final class Process: ObjectIdentifierProtocol {
             thread.start()
             self.stdout.thread = thread
 
-            // Close the write end of the stderr pipe.
-            try close(fd: &stderrPipe[1])
+            // Only schedule a thread for stderr if no redirect was requested.
+            if !outputRedirection.redirectStderr {
+                // Close the write end of the stderr pipe.
+                try close(fd: &stderrPipe[1])
 
-            // Create a thread and start reading the stderr output on it.
-            thread = Thread { [weak self] in
-                if let readResult = self?.readOutput(onFD: stderrPipe[0], outputClosure: outputClosures?.stderrClosure) {
-                    self?.stderr.result = readResult
+                // Create a thread and start reading the stderr output on it.
+                thread = Thread { [weak self] in
+                    if let readResult = self?.readOutput(onFD: stderrPipe[0], outputClosure: outputClosures?.stderrClosure) {
+                        self?.stderr.result = readResult
+                    }
                 }
+                thread.start()
+                self.stderr.thread = thread
             }
-            thread.start()
-            self.stderr.thread = thread
         }
       #endif // POSIX implementation
     }

Tests/TSCBasicTests/ProcessTests.swift

@@ -191,7 +191,7 @@ class ProcessTests: XCTestCase {
         do {
             let result = try Process.popen(args: script("simple-stdout-stderr"))
             XCTAssertEqual(try result.utf8Output(), "simple output\n")
-            XCTAssertEqual(try result.utf8stderrOutput(), "simple error")
+            XCTAssertEqual(try result.utf8stderrOutput(), "simple error\n")
         }
 
         // A long stdout and stderr output.
@@ -211,6 +211,60 @@ class ProcessTests: XCTestCase {
         }
     }
 
+    func testStdoutStdErrRedirected() throws {
+        // A simple script to check that stdout and stderr are captured in the same location.
+        do {
+            let process = Process(args: script("simple-stdout-stderr"), outputRedirection: .collect(redirectStderr: true))
+            try process.launch()
+            let result = try process.waitUntilExit()
+            XCTAssertEqual(try result.utf8Output(), "simple error\nsimple output\n")
+            XCTAssertEqual(try result.utf8stderrOutput(), "")
+        }
+
+        // A long stdout and stderr output.
+        do {
+            let process = Process(args: script("long-stdout-stderr"), outputRedirection: .collect(redirectStderr: true))
+            try process.launch()
+            let result = try process.waitUntilExit()
+
+            let count = 16 * 1024
+            XCTAssertEqual(try result.utf8Output(), String(repeating: "12", count: count))
+            XCTAssertEqual(try result.utf8stderrOutput(), "")
+        }
+    }
+
+    func testStdoutStdErrStreaming() throws {
+        var stdout = [UInt8]()
+        var stderr = [UInt8]()
+        let process = Process(args: script("long-stdout-stderr"), outputRedirection: .stream(stdout: { stdoutBytes in
+            stdout += stdoutBytes
+        }, stderr: { stderrBytes in
+            stderr += stderrBytes
+        }))
+        try process.launch()
+        try process.waitUntilExit()
+
+        let count = 16 * 1024
+        XCTAssertEqual(String(bytes: stdout, encoding: .utf8), String(repeating: "1", count: count))
+        XCTAssertEqual(String(bytes: stderr, encoding: .utf8), String(repeating: "2", count: count))
+    }
+
+    func testStdoutStdErrStreamingRedirected() throws {
+        var stdout = [UInt8]()
+        var stderr = [UInt8]()
+        let process = Process(args: script("long-stdout-stderr"), outputRedirection: .stream(stdout: { stdoutBytes in
+            stdout += stdoutBytes
+        }, stderr: { stderrBytes in
+            stderr += stderrBytes
+        }, redirectStderr: true))
+        try process.launch()
+        try process.waitUntilExit()
+
+        let count = 16 * 1024
+        XCTAssertEqual(String(bytes: stdout, encoding: .utf8), String(repeating: "12", count: count))
+        XCTAssertEqual(stderr, [])
+    }
+
     func testWorkingDirectory() throws {
         guard #available(macOS 10.15, *) else {
             // Skip this test since it's not supported in this OS.

Tests/TSCBasicTests/processInputs/simple-stdout-stderr

@@ -2,7 +2,7 @@
 
 import sys
 
-sys.stderr.write("simple error")
+sys.stderr.write("simple error\n")
 sys.stderr.flush()
 sys.stdout.write("simple output\n")
 sys.stdout.flush()