internal/configstore: do not require console for subprocess in windows

The configstore downloads the latest telemetry config using the
`go mod download` command. The uploader process that calls this
configstore is likely a daemonized process (see x/telemetry/start_windows.go)
and has no console attached.  The console creation behavior when
the parent is a console process without console is not clearly
documented anywhere, but empirically we observed a new console
(new window) is created for the subprocess. I am not sure if this
is due to the system default configuration, or due to how go's
os/exec is implemented on windows.

Prevent the new console creation by explicitly setting the
CREATE_NO_WINDOW attribute.
  https://learn.microsoft.com/en-us/windows/win32/procthread/process-creation-flags

Manually tested.

For golang/go#67660

Change-Id: Ia86ebafe3d4d7bcb63a7eaf9ce01c4eb32b43809
Reviewed-on: https://go-review.googlesource.com/c/telemetry/+/589061
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>

internal/configstore/download.go

@@ -25,6 +25,10 @@ const (
 	configFileName = "config.json"
 )
 
+// needNoConsole is used on windows to set the windows.CREATE_NO_WINDOW
+// creation flag.
+var needNoConsole = func(cmd *exec.Cmd) {}
+
 // Download fetches the requested telemetry UploadConfig using "go mod
 // download". If envOverlay is provided, it is appended to the environment used
 // for invoking the go command.
@@ -37,6 +41,7 @@ func Download(version string, envOverlay []string) (*telemetry.UploadConfig, str
 	modVer := ModulePath + "@" + version
 	var stdout, stderr bytes.Buffer
 	cmd := exec.Command("go", "mod", "download", "-json", modVer)
+	needNoConsole(cmd)
 	cmd.Env = append(os.Environ(), envOverlay...)
 	cmd.Stdout = &stdout
 	cmd.Stderr = &stderr

internal/configstore/download_windows.go

@@ -0,0 +1,33 @@
+// Copyright 2024 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build windows
+
+package configstore
+
+import (
+	"os/exec"
+	"syscall"
+
+	"golang.org/x/sys/windows"
+)
+
+func init() {
+	needNoConsole = needNoConsoleWindows
+}
+
+func needNoConsoleWindows(cmd *exec.Cmd) {
+	// The uploader main process is likely a daemonized process with no console.
+	// (see x/telemetry/start_windows.go) The console creation behavior when
+	// a parent is a console process without console is not clearly documented
+	// but empirically we observed the new console is created and attached to the
+	// subprocess in the default setup.
+	//
+	// Ensure no new console is attached to the subprocess by setting CREATE_NO_WINDOW.
+	//   https://learn.microsoft.com/en-us/windows/console/creation-of-a-console
+	//   https://learn.microsoft.com/en-us/windows/win32/procthread/process-creation-flags
+	cmd.SysProcAttr = &syscall.SysProcAttr{
+		CreationFlags: windows.CREATE_NO_WINDOW,
+	}
+}