Don't even start process alive check if platform does not support it (#3762)

Author: jakebailey

cmd/tsgo/isprocessalive_other.go

@@ -2,9 +2,8 @@
 
 package main
 
-// isProcessAlive on unsupported platforms always returns true,
-// meaning the watchdog will never fire. This is safe: the server
-// simply won't detect a dead parent on these platforms.
+const processAliveSupported = false
+
 func isProcessAlive(pid int) bool {
-	return true
+	panic("isProcessAlive is not supported on this platform")
 }

cmd/tsgo/isprocessalive_unix.go

@@ -8,6 +8,8 @@ import (
 	"syscall"
 )
 
+const processAliveSupported = true
+
 // isProcessAlive checks if a process with the given PID is still running.
 // On Unix, FindProcess always succeeds, so we send signal 0 to probe the
 // process. If the signal returns nil or EPERM, the process exists (EPERM

cmd/tsgo/isprocessalive_windows.go

@@ -4,6 +4,8 @@ package main
 
 import "syscall"
 
+const processAliveSupported = true
+
 // isProcessAlive checks if a process with the given PID is still running.
 // On Windows, we open the process with SYNCHRONIZE access and use
 // WaitForSingleObject with a zero timeout. If the wait times out, the

cmd/tsgo/lsp.go

@@ -60,10 +60,8 @@ func runLSP(args []string) int {
 			cmd.Dir = cwd
 			return cmd.Output()
 		},
-		ProgressDelay: 250 * time.Millisecond,
-		SetParentProcessID: func(parentPID int) {
-			startParentProcessWatchdog(ctx, stop, parentPID)
-		},
+		ProgressDelay:      250 * time.Millisecond,
+		SetParentProcessID: newParentProcessWatchdog(ctx, stop),
 	})
 
 	if err := s.Run(ctx); err != nil {
@@ -73,6 +71,17 @@ func runLSP(args []string) int {
 	return 0
 }
 
+// newParentProcessWatchdog returns a SetParentProcessID callback if the platform
+// supports process-alive checking, or nil otherwise.
+func newParentProcessWatchdog(ctx context.Context, stop context.CancelFunc) func(int) {
+	if !processAliveSupported {
+		return nil
+	}
+	return func(parentPID int) {
+		startParentProcessWatchdog(ctx, stop, parentPID)
+	}
+}
+
 // startParentProcessWatchdog starts a goroutine that monitors the parent process
 // and cancels the context if the parent dies. This prevents orphaned language
 // server processes when the editor crashes or is killed.