gopls: record telemetry counters for settings that are used

Instrument telemetry recording which settings are passed to gopls.
In some cases, this merely records whether settings were set. In others,
it records buckets for the setting value.

Fixes golang/go#71285

Change-Id: I820318fe9cf1b05accb3105e5e2d6ddc3c5e768f
Reviewed-on: https://go-review.googlesource.com/c/tools/+/648416
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Alan Donovan <[email protected]>
Auto-Submit: Robert Findley <[email protected]>

Author: findleyr

gopls/internal/cache/session_test.go

@@ -337,7 +337,8 @@ replace (
 			for _, f := range test.folders {
 				opts := settings.DefaultOptions()
 				if f.options != nil {
-					for _, err := range opts.Set(f.options(dir)) {
+					_, errs := opts.Set(f.options(dir))
+					for _, err := range errs {
 						t.Fatal(err)
 					}
 				}

gopls/internal/server/general.go

@@ -28,6 +28,7 @@ import (
 	"golang.org/x/tools/gopls/internal/protocol"
 	"golang.org/x/tools/gopls/internal/protocol/semtok"
 	"golang.org/x/tools/gopls/internal/settings"
+	"golang.org/x/tools/gopls/internal/telemetry"
 	"golang.org/x/tools/gopls/internal/util/bug"
 	"golang.org/x/tools/gopls/internal/util/goversion"
 	"golang.org/x/tools/gopls/internal/util/moremaps"
@@ -74,7 +75,11 @@ func (s *server) Initialize(ctx context.Context, params *protocol.ParamInitializ
 	// TODO(rfindley): eliminate this defer.
 	defer func() { s.SetOptions(options) }()
 
-	s.handleOptionErrors(ctx, options.Set(params.InitializationOptions))
+	// Process initialization options.
+	{
+		res, errs := options.Set(params.InitializationOptions)
+		s.handleOptionResult(ctx, res, errs)
+	}
 	options.ForClientCapabilities(params.ClientInfo, params.Capabilities)
 
 	if options.ShowBugReports {
@@ -541,7 +546,8 @@ func (s *server) fetchFolderOptions(ctx context.Context, folder protocol.Documen
 
 	opts = opts.Clone()
 	for _, config := range configs {
-		s.handleOptionErrors(ctx, opts.Set(config))
+		res, errs := opts.Set(config)
+		s.handleOptionResult(ctx, res, errs)
 	}
 	return opts, nil
 }
@@ -555,7 +561,12 @@ func (s *server) eventuallyShowMessage(ctx context.Context, msg *protocol.ShowMe
 	s.notifications = append(s.notifications, msg)
 }
 
-func (s *server) handleOptionErrors(ctx context.Context, optionErrors []error) {
+func (s *server) handleOptionResult(ctx context.Context, applied []telemetry.CounterPath, optionErrors []error) {
+	for _, path := range applied {
+		path = append(settings.CounterPath{"gopls", "setting"}, path...)
+		counter.Inc(path.FullName())
+	}
+
 	var warnings, errs []string
 	for _, err := range optionErrors {
 		if err == nil {