Introduce FileDescriptorInput.standardInput, FileDescriptorOutput.standardOutput, and FileDescriptorOutput.standardError to easily bind current process' descriptors to child processes

Sources/Subprocess/Configuration.swift

@@ -103,6 +103,10 @@ public struct Configuration: Sendable {
         var _spawnResult = spawnResultBox!.take()!
 
         let execution = _spawnResult.execution
+        defer {
+            // Close process file descriptor now we finished monitoring
+            execution.processIdentifier.close()
+        }
 
         return try await withAsyncTaskCleanupHandler {
             let inputIO = _spawnResult.inputWriteEnd()
@@ -127,9 +131,6 @@ public struct Configuration: Sendable {
                 for: execution.processIdentifier
             )
 
-            // Close process file descriptor now we finished monitoring
-            execution.processIdentifier.close()
-
             return ExecutionResult(
                 terminationStatus: terminationStatus,
                 value: try result.get()

Sources/Subprocess/IO/AsyncIO+Linux.swift

@@ -288,7 +288,7 @@ final class AsyncIO: Sendable {
                 )
                 if rc != 0 {
                     _registration.withLock { storage in
-                        storage.removeValue(forKey: fileDescriptor.rawValue)
+                        _ = storage.removeValue(forKey: fileDescriptor.rawValue)
                     }
 
                     let capturedError = errno

Sources/Subprocess/IO/Input.swift

@@ -179,6 +179,17 @@ extension InputProtocol where Self == FileDescriptorInput {
             closeAfterSpawningProcess: closeAfterSpawningProcess
         )
     }
+
+    /// Create a Subprocess input that reads from the standard input of
+    /// current process.
+    ///
+    /// The file descriptor isn't closed afterwards.
+    public static var standardInput: Self {
+        return Self.fileDescriptor(
+            .standardInput,
+            closeAfterSpawningProcess: false
+        )
+    }
 }
 
 extension InputProtocol {

Sources/Subprocess/IO/Output.swift

@@ -231,6 +231,28 @@ extension OutputProtocol where Self == FileDescriptorOutput {
     ) -> Self {
         return .init(fileDescriptor: fd, closeAfterSpawningProcess: closeAfterSpawningProcess)
     }
+
+    /// Create a Subprocess output that writes output to the standard output of
+    /// current process.
+    ///
+    /// The file descriptor isn't closed afterwards.
+    public static var standardOutput: Self {
+        return Self.fileDescriptor(
+            .standardOutput,
+            closeAfterSpawningProcess: false
+        )
+    }
+
+    /// Create a Subprocess output that write output to the standard error of
+    /// current process.
+    ///
+    /// The file descriptor isn't closed afterwards.
+    public static var standardError: Self {
+        return Self.fileDescriptor(
+            .standardError,
+            closeAfterSpawningProcess: false
+        )
+    }
 }
 
 extension OutputProtocol where Self == StringOutput<UTF8> {