gopls/internal/server: respect SemanticTokens option during initialization

Previously, the Initialize method unconditionally advertised support for
semantic tokens via the SemanticTokensProvider capability. This caused
clients (such as VS Code) to send semantic token requests even if the
user had configured "semanticTokens": false.

The performance overhead of these requests was small, as gopls already
checks the option when handling requests and returns an empty response
if disabled.

However, omitting the SemanticTokensProvider capability when the option
is disabled will save a few roundtrips and result in less noise in the
logs.

Change-Id: If36b2e0752f9ca42cfaf6b458ae96d5ffeaea6e9
Reviewed-on: https://go-review.googlesource.com/c/tools/+/740920
Reviewed-by: Alan Donovan <adonovan@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Alan Donovan <adonovan@google.com>
Reviewed-by: Madeline Kalil <mkalil@google.com>

Author: leitzler

gopls/doc/settings.md

@@ -210,8 +210,9 @@ Default: `{"generate":true,"regenerate_cgo":true,"run_govulncheck":true,"tidy":t
 
 **This setting is experimental and may be deleted.**
 
-semanticTokens controls whether the LSP server will send
-semantic tokens to the client.
+semanticTokens determines whether gopls will return a
+SemanticTokensProvider at initialization, or respond
+to request for semantic tokens.
 
 Default: `false`.
 

gopls/internal/doc/api.json

@@ -2113,7 +2113,7 @@
 			{
 				"Name": "semanticTokens",
 				"Type": "bool",
-				"Doc": "semanticTokens controls whether the LSP server will send\nsemantic tokens to the client.\n",
+				"Doc": "semanticTokens determines whether gopls will return a\nSemanticTokensProvider at initialization, or respond\nto request for semantic tokens.\n",
 				"EnumKeys": {
 					"ValueType": "",
 					"Keys": null

gopls/internal/server/general.go

@@ -123,6 +123,18 @@ func (s *server) Initialize(ctx context.Context, params *protocol.ParamInitializ
 		}
 	}
 
+	var semanticTokenProvider any
+	if options.SemanticTokens {
+		semanticTokenProvider = protocol.SemanticTokensOptions{
+			Range: &protocol.Or_SemanticTokensOptions_range{Value: true},
+			Full:  &protocol.Or_SemanticTokensOptions_full{Value: true},
+			Legend: protocol.SemanticTokensLegend{
+				TokenTypes:     moreslices.ConvertStrings[string](semtok.Types),
+				TokenModifiers: moreslices.ConvertStrings[string](semtok.Modifiers),
+			},
+		}
+	}
+
 	versionInfo := debug.VersionInfo()
 
 	goplsVersion, err := json.Marshal(versionInfo)
@@ -156,14 +168,7 @@ func (s *server) Initialize(ctx context.Context, params *protocol.ParamInitializ
 			ReferencesProvider:        &protocol.Or_ServerCapabilities_referencesProvider{Value: true},
 			RenameProvider:            renameOpts,
 			SelectionRangeProvider:    &protocol.Or_ServerCapabilities_selectionRangeProvider{Value: true},
-			SemanticTokensProvider: protocol.SemanticTokensOptions{
-				Range: &protocol.Or_SemanticTokensOptions_range{Value: true},
-				Full:  &protocol.Or_SemanticTokensOptions_full{Value: true},
-				Legend: protocol.SemanticTokensLegend{
-					TokenTypes:     moreslices.ConvertStrings[string](semtok.Types),
-					TokenModifiers: moreslices.ConvertStrings[string](semtok.Modifiers),
-				},
-			},
+			SemanticTokensProvider:    semanticTokenProvider,
 			SignatureHelpProvider: &protocol.SignatureHelpOptions{
 				TriggerCharacters: []string{"(", ","},
 				// Used to update or dismiss signature help when it's already active,

gopls/internal/settings/settings.go

@@ -225,8 +225,9 @@ type UIOptions struct {
 	// ```
 	Codelenses map[CodeLensSource]bool
 
-	// SemanticTokens controls whether the LSP server will send
-	// semantic tokens to the client.
+	// SemanticTokens determines whether gopls will return a
+	// SemanticTokensProvider at initialization, or respond
+	// to request for semantic tokens.
 	SemanticTokens bool `status:"experimental"`
 
 	// NoSemanticString turns off the sending of the semantic token 'string'