syscall: don't check non-existent return code in GetStartupInfo

Fixes #31316

Change-Id: I1ca5968836e7bcad91496e4ed3cf1a0caf1375f1
Reviewed-on: https://go-review.googlesource.com/c/go/+/520275
Run-TryBot: Tobias Klauser <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Tobias Klauser <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>

Author: tklauser

src/syscall/syscall_windows.go

@@ -264,7 +264,7 @@ func NewCallbackCDecl(fn any) uintptr {
 //sys	OpenProcess(da uint32, inheritHandle bool, pid uint32) (handle Handle, err error)
 //sys	TerminateProcess(handle Handle, exitcode uint32) (err error)
 //sys	GetExitCodeProcess(handle Handle, exitcode *uint32) (err error)
-//sys	GetStartupInfo(startupInfo *StartupInfo) (err error) = GetStartupInfoW
+//sys	getStartupInfo(startupInfo *StartupInfo) = GetStartupInfoW
 //sys	GetCurrentProcess() (pseudoHandle Handle, err error)
 //sys	GetProcessTimes(handle Handle, creationTime *Filetime, exitTime *Filetime, kernelTime *Filetime, userTime *Filetime) (err error)
 //sys	DuplicateHandle(hSourceProcessHandle Handle, hSourceHandle Handle, hTargetProcessHandle Handle, lpTargetHandle *Handle, dwDesiredAccess uint32, bInheritHandle bool, dwOptions uint32) (err error)
@@ -1437,3 +1437,8 @@ func newProcThreadAttributeList(maxAttrCount uint32) (*_PROC_THREAD_ATTRIBUTE_LI
 func RegEnumKeyEx(key Handle, index uint32, name *uint16, nameLen *uint32, reserved *uint32, class *uint16, classLen *uint32, lastWriteTime *Filetime) (regerrno error) {
 	return regEnumKeyEx(key, index, name, nameLen, reserved, class, classLen, lastWriteTime)
 }
+
+func GetStartupInfo(startupInfo *StartupInfo) error {
+	getStartupInfo(startupInfo)
+	return nil
+}

src/syscall/syscall_windows_test.go

@@ -204,6 +204,15 @@ func TestGetwd_DoesNotPanicWhenPathIsLong(t *testing.T) {
 	syscall.Getwd()
 }
 
+func TestGetStartupInfo(t *testing.T) {
+	var si syscall.StartupInfo
+	err := syscall.GetStartupInfo(&si)
+	if err != nil {
+		// see https://go.dev/issue/31316
+		t.Fatalf("GetStartupInfo: got error %v, want nil", err)
+	}
+}
+
 func FuzzUTF16FromString(f *testing.F) {
 	f.Add("hi")           // ASCII
 	f.Add("â")            // latin1