gopls/internal/cmd: implement counters for mcp server

Adds three new counters for tracking usage of the Go MCP
Server that increment when a user starts up the server
in attached or headless mode.

For golang/go#74291

Change-Id: Ifa324f1151371aac68f1cde63f0d7966a95e97dd
Reviewed-on: https://go-review.googlesource.com/c/tools/+/683315
Auto-Submit: Madeline Kalil <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Robert Findley <[email protected]>

Author: madelinekalil

gopls/internal/cmd/counters.go

@@ -0,0 +1,15 @@
+// Copyright 2025 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.
+
+package cmd
+
+import "golang.org/x/telemetry/counter"
+
+// Proposed counters for evaluating usage of the Go MCP Server. These counters
+// increment when the user starts up the server in attached or headless mode.
+var (
+	countHeadlessMCPStdIO = counter.New("gopls/mcp-headless:stdio")
+	countHeadlessMCPSSE   = counter.New("gopls/mcp-headless:sse")
+	countAttachedMCP      = counter.New("gopls/mcp")
+)

gopls/internal/cmd/mcp.go

@@ -47,6 +47,7 @@ func (m *headlessMCP) Run(ctx context.Context, args ...string) error {
 
 	// Send a SessionStart event to trigger creation of an http handler.
 	if m.Address != "" {
+		countHeadlessMCPSSE.Inc()
 		// Specify a channel size of two so that the send operations are
 		// non-blocking.
 		eventChan := make(chan lsprpc.SessionEvent, 2)
@@ -65,6 +66,7 @@ func (m *headlessMCP) Run(ctx context.Context, args ...string) error {
 
 		return mcp.Serve(ctx, m.Address, eventChan, false)
 	} else {
+		countHeadlessMCPStdIO.Inc()
 		return mcp.StartStdIO(ctx, sess)
 	}
 }

gopls/internal/cmd/serve.go

@@ -126,6 +126,7 @@ func (s *Serve) Run(ctx context.Context, args ...string) error {
 
 	// Start MCP server.
 	if eventChan != nil {
+		countAttachedMCP.Inc()
 		group.Go(func() (err error) {
 			defer func() {
 				if err == nil {