Fix unused identifier diags, LSP tag diags

internal/checker/checker.go

@@ -2130,7 +2130,7 @@ func (c *Checker) checkSourceFile(ctx context.Context, sourceFile *ast.SourceFil
 		}
 		if ctx.Err() == nil {
 			// This relies on the results of other lazy diagnostics, so must be computed after them
-			if !sourceFile.IsDeclarationFile && (c.compilerOptions.NoUnusedLocals.IsTrue() || c.compilerOptions.NoUnusedParameters.IsTrue()) {
+			if !sourceFile.IsDeclarationFile {
 				c.checkUnusedIdentifiers(links.identifierCheckNodes)
 			}
 			if !sourceFile.IsDeclarationFile {
@@ -6781,10 +6781,26 @@ func (c *Checker) reportUnusedVariable(location *ast.Node, diagnostic *ast.Diagn
 }
 
 func (c *Checker) reportUnused(location *ast.Node, kind UnusedKind, diagnostic *ast.Diagnostic) {
-	if location.Flags&(ast.NodeFlagsAmbient|ast.NodeFlagsThisNodeOrAnySubNodesHasError) == 0 &&
-		(kind == UnusedKindLocal && c.compilerOptions.NoUnusedLocals.IsTrue() ||
-			(kind == UnusedKindParameter && c.compilerOptions.NoUnusedParameters.IsTrue())) {
-		c.diagnostics.Add(diagnostic)
+	if location.Flags&(ast.NodeFlagsAmbient|ast.NodeFlagsThisNodeOrAnySubNodesHasError) == 0 {
+		isError := c.unusedIsError(kind)
+		if isError {
+			c.diagnostics.Add(diagnostic)
+		} else {
+			suggestion := *diagnostic
+			suggestion.SetCategory(diagnostics.CategorySuggestion)
+			c.suggestionDiagnostics.Add(&suggestion)
+		}
+	}
+}
+
+func (c *Checker) unusedIsError(kind UnusedKind) bool {
+	switch kind {
+	case UnusedKindLocal:
+		return c.compilerOptions.NoUnusedLocals.IsTrue()
+	case UnusedKindParameter:
+		return c.compilerOptions.NoUnusedParameters.IsTrue()
+	default:
+		panic("Unhandled case in unusedIsError")
 	}
 }
 

internal/fourslash/fourslash.go

@@ -270,12 +270,6 @@ func getCapabilitiesWithDefaults(capabilities *lsproto.ClientCapabilities) *lspr
 	if capabilitiesWithDefaults.TextDocument.Diagnostic == nil {
 		capabilitiesWithDefaults.TextDocument.Diagnostic = &lsproto.DiagnosticClientCapabilities{
 			RelatedInformation: ptrTrue,
-			TagSupport: &lsproto.ClientDiagnosticsTagOptions{
-				ValueSet: []lsproto.DiagnosticTag{
-					lsproto.DiagnosticTagUnnecessary,
-					lsproto.DiagnosticTagDeprecated,
-				},
-			},
 		}
 	}
 	if capabilitiesWithDefaults.Workspace == nil {

internal/ls/diagnostics.go

@@ -2,7 +2,6 @@ package ls
 
 import (
 	"context"
-	"slices"
 	"strings"
 
 	"github.com/microsoft/typescript-go/internal/ast"
@@ -20,6 +19,7 @@ func (l *LanguageService) ProvideDiagnostics(ctx context.Context, uri lsproto.Do
 	diagnostics = append(diagnostics, program.GetSemanticDiagnostics(ctx, file))
 	// !!! user preference for suggestion diagnostics; keep only unnecessary/deprecated?
 	// See: https://github.com/microsoft/vscode/blob/3dbc74129aaae102e5cb485b958fa5360e8d3e7a/extensions/typescript-language-features/src/languageFeatures/diagnostics.ts#L114
+	// TODO: also implement reportStyleCheckAsWarnings to rewrite diags with Warning severity
 	diagnostics = append(diagnostics, program.GetSuggestionDiagnostics(ctx, file))
 	if program.Options().GetEmitDeclarations() {
 		diagnostics = append(diagnostics, program.GetDeclarationDiagnostics(ctx, file))
@@ -73,13 +73,14 @@ func (l *LanguageService) toLSPDiagnostic(clientOptions *lsproto.DiagnosticClien
 		}
 	}
 
+	// We do not check client capabilities for tags; the LSP spec says clients must handle unknown tags.
 	var tags []lsproto.DiagnosticTag
-	if clientOptions != nil && clientOptions.TagSupport != nil && (diagnostic.ReportsUnnecessary() || diagnostic.ReportsDeprecated()) {
+	if diagnostic.ReportsUnnecessary() || diagnostic.ReportsDeprecated() {
 		tags = make([]lsproto.DiagnosticTag, 0, 2)
-		if diagnostic.ReportsUnnecessary() && slices.Contains(clientOptions.TagSupport.ValueSet, lsproto.DiagnosticTagUnnecessary) {
+		if diagnostic.ReportsUnnecessary() {
 			tags = append(tags, lsproto.DiagnosticTagUnnecessary)
 		}
-		if diagnostic.ReportsDeprecated() && slices.Contains(clientOptions.TagSupport.ValueSet, lsproto.DiagnosticTagDeprecated) {
+		if diagnostic.ReportsDeprecated() {
 			tags = append(tags, lsproto.DiagnosticTagDeprecated)
 		}
 	}