Fix an issue where process handles are leaked in exec on Windows

Because _exit immediately terminates the process, the CloseHandle calls in the defer blocks in the body of the exec function are never called. This leads to the handles leaking on Windows. Move the body of the function into a do block above the _exit call to resolve this.

Author: jakepetroules

Sources/TSCBasic/misc.swift

@@ -93,71 +93,74 @@ private func quote(_ arguments: [String]) -> String {
 public func exec(path: String, args: [String]) throws -> Never {
     let cArgs = CStringArray(args)
   #if os(Windows)
-    var hJob: HANDLE
+    // Wrap body in a do block to ensure closing handles in defer blocks occurs prior to the call to _exit
+    var dwExitCode: DWORD = DWORD(bitPattern: -1)
+    do {
+        var hJob: HANDLE
 
-    hJob = CreateJobObjectA(nil, nil)
-    if hJob == HANDLE(bitPattern: 0) {
-        throw SystemError.exec(Int32(GetLastError()), path: path, args: args)
-    }
-    defer { CloseHandle(hJob) }
+        hJob = CreateJobObjectA(nil, nil)
+        if hJob == HANDLE(bitPattern: 0) {
+            throw SystemError.exec(Int32(GetLastError()), path: path, args: args)
+        }
+        defer { CloseHandle(hJob) }
 
-    let hPort = CreateIoCompletionPort(INVALID_HANDLE_VALUE, nil, 0, 1)
-    if hPort == HANDLE(bitPattern: 0) {
-        throw SystemError.exec(Int32(GetLastError()), path: path, args: args)
-    }
+        let hPort = CreateIoCompletionPort(INVALID_HANDLE_VALUE, nil, 0, 1)
+        if hPort == HANDLE(bitPattern: 0) {
+            throw SystemError.exec(Int32(GetLastError()), path: path, args: args)
+        }
 
-    var acpAssociation: JOBOBJECT_ASSOCIATE_COMPLETION_PORT = JOBOBJECT_ASSOCIATE_COMPLETION_PORT()
-    acpAssociation.CompletionKey = hJob
-    acpAssociation.CompletionPort = hPort
-    if !SetInformationJobObject(hJob, JobObjectAssociateCompletionPortInformation,
-                                &acpAssociation, DWORD(MemoryLayout<JOBOBJECT_ASSOCIATE_COMPLETION_PORT>.size)) {
-        throw SystemError.exec(Int32(GetLastError()), path: path, args: args)
-    }
+        var acpAssociation: JOBOBJECT_ASSOCIATE_COMPLETION_PORT = JOBOBJECT_ASSOCIATE_COMPLETION_PORT()
+        acpAssociation.CompletionKey = hJob
+        acpAssociation.CompletionPort = hPort
+        if !SetInformationJobObject(hJob, JobObjectAssociateCompletionPortInformation,
+                                    &acpAssociation, DWORD(MemoryLayout<JOBOBJECT_ASSOCIATE_COMPLETION_PORT>.size)) {
+            throw SystemError.exec(Int32(GetLastError()), path: path, args: args)
+        }
 
-    var eliLimits: JOBOBJECT_EXTENDED_LIMIT_INFORMATION = JOBOBJECT_EXTENDED_LIMIT_INFORMATION()
-    eliLimits.BasicLimitInformation.LimitFlags =
-            DWORD(JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE) | DWORD(JOB_OBJECT_LIMIT_SILENT_BREAKAWAY_OK)
-    if !SetInformationJobObject(hJob, JobObjectExtendedLimitInformation, &eliLimits,
-                                DWORD(MemoryLayout<JOBOBJECT_EXTENDED_LIMIT_INFORMATION>.size)) {
-        throw SystemError.exec(Int32(GetLastError()), path: path, args: args)
-    }
+        var eliLimits: JOBOBJECT_EXTENDED_LIMIT_INFORMATION = JOBOBJECT_EXTENDED_LIMIT_INFORMATION()
+        eliLimits.BasicLimitInformation.LimitFlags =
+        DWORD(JOB_OBJECT_LIMIT_KILL_ON_JOB_CLOSE) | DWORD(JOB_OBJECT_LIMIT_SILENT_BREAKAWAY_OK)
+        if !SetInformationJobObject(hJob, JobObjectExtendedLimitInformation, &eliLimits,
+                                    DWORD(MemoryLayout<JOBOBJECT_EXTENDED_LIMIT_INFORMATION>.size)) {
+            throw SystemError.exec(Int32(GetLastError()), path: path, args: args)
+        }
 
 
-    var siInfo: STARTUPINFOW = STARTUPINFOW()
-    siInfo.cb = DWORD(MemoryLayout<STARTUPINFOW>.size)
+        var siInfo: STARTUPINFOW = STARTUPINFOW()
+        siInfo.cb = DWORD(MemoryLayout<STARTUPINFOW>.size)
 
-    var piInfo: PROCESS_INFORMATION = PROCESS_INFORMATION()
+        var piInfo: PROCESS_INFORMATION = PROCESS_INFORMATION()
 
-    try quote(args).withCString(encodedAs: UTF16.self) { pwszCommandLine in
-        if !CreateProcessW(nil,
-                           UnsafeMutablePointer<WCHAR>(mutating: pwszCommandLine),
-                           nil, nil, false,
-                           DWORD(CREATE_SUSPENDED) | DWORD(CREATE_NEW_PROCESS_GROUP),
-                           nil, nil, &siInfo, &piInfo) {
-            throw SystemError.exec(Int32(GetLastError()), path: path, args: args)
+        try quote(args).withCString(encodedAs: UTF16.self) { pwszCommandLine in
+            if !CreateProcessW(nil,
+                               UnsafeMutablePointer<WCHAR>(mutating: pwszCommandLine),
+                               nil, nil, false,
+                               DWORD(CREATE_SUSPENDED) | DWORD(CREATE_NEW_PROCESS_GROUP),
+                               nil, nil, &siInfo, &piInfo) {
+                throw SystemError.exec(Int32(GetLastError()), path: path, args: args)
+            }
         }
-    }
 
-    defer { CloseHandle(piInfo.hThread) }
-    defer { CloseHandle(piInfo.hProcess) }
+        defer { CloseHandle(piInfo.hThread) }
+        defer { CloseHandle(piInfo.hProcess) }
 
-    if !AssignProcessToJobObject(hJob, piInfo.hProcess) {
-        throw SystemError.exec(Int32(GetLastError()), path: path, args: args)
-    }
+        if !AssignProcessToJobObject(hJob, piInfo.hProcess) {
+            throw SystemError.exec(Int32(GetLastError()), path: path, args: args)
+        }
 
-    _ = ResumeThread(piInfo.hThread)
+        _ = ResumeThread(piInfo.hThread)
 
-    var dwCompletionCode: DWORD = 0
-    var ulCompletionKey: ULONG_PTR = 0
-    var lpOverlapped: LPOVERLAPPED?
-    repeat {
-    } while GetQueuedCompletionStatus(hPort, &dwCompletionCode, &ulCompletionKey,
-                                      &lpOverlapped, INFINITE) &&
-            !(ulCompletionKey == ULONG_PTR(UInt(bitPattern: hJob)) &&
-              dwCompletionCode == JOB_OBJECT_MSG_ACTIVE_PROCESS_ZERO)
+        var dwCompletionCode: DWORD = 0
+        var ulCompletionKey: ULONG_PTR = 0
+        var lpOverlapped: LPOVERLAPPED?
+        repeat {
+        } while GetQueuedCompletionStatus(hPort, &dwCompletionCode, &ulCompletionKey,
+                                          &lpOverlapped, INFINITE) &&
+        !(ulCompletionKey == ULONG_PTR(UInt(bitPattern: hJob)) &&
+          dwCompletionCode == JOB_OBJECT_MSG_ACTIVE_PROCESS_ZERO)
 
-    var dwExitCode: DWORD = DWORD(bitPattern: -1)
-    _ = GetExitCodeProcess(piInfo.hProcess, &dwExitCode)
+        _ = GetExitCodeProcess(piInfo.hProcess, &dwExitCode)
+    }
     _exit(Int32(bitPattern: dwExitCode))
   #elseif (!canImport(Darwin) || os(macOS))
     guard execv(path, cArgs.cArray) != -1 else {