Expose bind diags in LSP, show dead/deprecated code

internal/ast/diagnostic.go

@@ -19,6 +19,8 @@ type Diagnostic struct {
 	message            string
 	messageChain       []*Diagnostic
 	relatedInformation []*Diagnostic
+	reportsUnnecessary bool
+	reportsDeprecated  bool
 }
 
 func (d *Diagnostic) File() *SourceFile                 { return d.file }
@@ -31,6 +33,8 @@ func (d *Diagnostic) Category() diagnostics.Category    { return d.category }
 func (d *Diagnostic) Message() string                   { return d.message }
 func (d *Diagnostic) MessageChain() []*Diagnostic       { return d.messageChain }
 func (d *Diagnostic) RelatedInformation() []*Diagnostic { return d.relatedInformation }
+func (d *Diagnostic) ReportsUnnecessary() bool          { return d.reportsUnnecessary }
+func (d *Diagnostic) ReportsDeprecated() bool           { return d.reportsDeprecated }
 
 func (d *Diagnostic) SetFile(file *SourceFile)                  { d.file = file }
 func (d *Diagnostic) SetLocation(loc core.TextRange)            { d.loc = loc }
@@ -67,11 +71,13 @@ func (d *Diagnostic) Clone() *Diagnostic {
 
 func NewDiagnostic(file *SourceFile, loc core.TextRange, message *diagnostics.Message, args ...any) *Diagnostic {
 	return &Diagnostic{
-		file:     file,
-		loc:      loc,
-		code:     message.Code(),
-		category: message.Category(),
-		message:  message.Format(args...),
+		file:               file,
+		loc:                loc,
+		code:               message.Code(),
+		category:           message.Category(),
+		message:            message.Format(args...),
+		reportsUnnecessary: message.ReportsUnnecessary(),
+		reportsDeprecated:  message.ReportsDeprecated(),
 	}
 }
 

internal/checker/checker.go

@@ -13153,21 +13153,29 @@ func (c *Checker) getCannotFindNameDiagnosticForName(node *ast.Node) *diagnostic
 }
 
 func (c *Checker) GetDiagnostics(ctx context.Context, sourceFile *ast.SourceFile) []*ast.Diagnostic {
+	return c.getDiagnostics(ctx, sourceFile, &c.diagnostics)
+}
+
+func (c *Checker) GetSuggestionDiagnostics(ctx context.Context, sourceFile *ast.SourceFile) []*ast.Diagnostic {
+	return c.getDiagnostics(ctx, sourceFile, &c.suggestionDiagnostics)
+}
+
+func (c *Checker) getDiagnostics(ctx context.Context, sourceFile *ast.SourceFile, collection *ast.DiagnosticsCollection) []*ast.Diagnostic {
 	c.checkNotCanceled()
 	if sourceFile != nil {
 		c.CheckSourceFile(ctx, sourceFile)
 		if c.wasCanceled {
 			return nil
 		}
-		return c.diagnostics.GetDiagnosticsForFile(sourceFile.FileName())
+		return collection.GetDiagnosticsForFile(sourceFile.FileName())
 	}
 	for _, file := range c.files {
 		c.CheckSourceFile(ctx, file)
 		if c.wasCanceled {
 			return nil
 		}
 	}
-	return c.diagnostics.GetDiagnostics()
+	return collection.GetDiagnostics()
 }
 
 func (c *Checker) GetDiagnosticsWithoutCheck(sourceFile *ast.SourceFile) []*ast.Diagnostic {

internal/compiler/program.go

@@ -348,6 +348,10 @@ func (p *Program) GetSemanticDiagnostics(ctx context.Context, sourceFile *ast.So
 	return p.getDiagnosticsHelper(ctx, sourceFile, true /*ensureBound*/, true /*ensureChecked*/, p.getSemanticDiagnosticsForFile)
 }
 
+func (p *Program) GetSuggestionDiagnostics(ctx context.Context, sourceFile *ast.SourceFile) []*ast.Diagnostic {
+	return p.getDiagnosticsHelper(ctx, sourceFile, true /*ensureBound*/, true /*ensureChecked*/, p.getSuggestionDiagnosticsForFile)
+}
+
 func (p *Program) GetGlobalDiagnostics(ctx context.Context) []*ast.Diagnostic {
 	var globalDiagnostics []*ast.Diagnostic
 	checkers, done := p.checkerPool.GetAllCheckers(ctx)
@@ -452,6 +456,39 @@ func (p *Program) getSemanticDiagnosticsForFile(ctx context.Context, sourceFile
 	return filtered
 }
 
+func (p *Program) getSuggestionDiagnosticsForFile(ctx context.Context, sourceFile *ast.SourceFile) []*ast.Diagnostic {
+	if checker.SkipTypeChecking(sourceFile, p.compilerOptions) {
+		return nil
+	}
+
+	var fileChecker *checker.Checker
+	var done func()
+	if sourceFile != nil {
+		fileChecker, done = p.checkerPool.GetCheckerForFile(ctx, sourceFile)
+		defer done()
+	}
+
+	diags := slices.Clip(sourceFile.BindSuggestionDiagnostics)
+
+	checkers, closeCheckers := p.checkerPool.GetAllCheckers(ctx)
+	defer closeCheckers()
+
+	// Ask for diags from all checkers; checking one file may add diagnostics to other files.
+	// These are deduplicated later.
+	for _, checker := range checkers {
+		if sourceFile == nil || checker == fileChecker {
+			diags = append(diags, checker.GetSuggestionDiagnostics(ctx, sourceFile)...)
+		} else {
+			// !!! is there any case where suggestion diagnostics are produced in other checkers?
+		}
+	}
+	if ctx.Err() != nil {
+		return nil
+	}
+
+	return diags
+}
+
 func isCommentOrBlankLine(text string, pos int) bool {
 	for pos < len(text) && (text[pos] == ' ' || text[pos] == '\t') {
 		pos++

internal/ls/diagnostics.go

@@ -13,17 +13,21 @@ func (l *LanguageService) GetDocumentDiagnostics(ctx context.Context, documentUR
 	syntaxDiagnostics := program.GetSyntacticDiagnostics(ctx, file)
 	var lspDiagnostics []*lsproto.Diagnostic
 	if len(syntaxDiagnostics) != 0 {
-		lspDiagnostics = make([]*lsproto.Diagnostic, len(syntaxDiagnostics))
-		for i, diag := range syntaxDiagnostics {
-			lspDiagnostics[i] = toLSPDiagnostic(diag, l.converters)
+		lspDiagnostics = make([]*lsproto.Diagnostic, 0, len(syntaxDiagnostics))
+		for _, diag := range syntaxDiagnostics {
+			lspDiagnostics = append(lspDiagnostics, toLSPDiagnostic(diag, l.converters))
 		}
 	} else {
-		checker, done := program.GetTypeCheckerForFile(ctx, file)
-		defer done()
-		semanticDiagnostics := checker.GetDiagnostics(ctx, file)
-		lspDiagnostics = make([]*lsproto.Diagnostic, len(semanticDiagnostics))
-		for i, diag := range semanticDiagnostics {
-			lspDiagnostics[i] = toLSPDiagnostic(diag, l.converters)
+		diagnostics := program.GetSemanticDiagnostics(ctx, file)
+		suggestionDiagnostics := program.GetSuggestionDiagnostics(ctx, file)
+
+		lspDiagnostics = make([]*lsproto.Diagnostic, 0, len(diagnostics)+len(suggestionDiagnostics))
+		for _, diag := range diagnostics {
+			lspDiagnostics = append(lspDiagnostics, toLSPDiagnostic(diag, l.converters))
+		}
+		for _, diag := range suggestionDiagnostics {
+			// !!! user preference for suggestion diagnostics; keep only unnecessary/dprecated?
+			lspDiagnostics = append(lspDiagnostics, toLSPDiagnostic(diag, l.converters))
 		}
 	}
 	return &lsproto.DocumentDiagnosticReport{
@@ -60,6 +64,17 @@ func toLSPDiagnostic(diagnostic *ast.Diagnostic, converters *Converters) *lsprot
 		})
 	}
 
+	var tags []lsproto.DiagnosticTag
+	if diagnostic.ReportsUnnecessary() || diagnostic.ReportsDeprecated() {
+		tags = make([]lsproto.DiagnosticTag, 0, 2)
+		if diagnostic.ReportsUnnecessary() {
+			tags = append(tags, lsproto.DiagnosticTagUnnecessary)
+		}
+		if diagnostic.ReportsDeprecated() {
+			tags = append(tags, lsproto.DiagnosticTagDeprecated)
+		}
+	}
+
 	return &lsproto.Diagnostic{
 		Range: converters.ToLSPRange(diagnostic.File(), diagnostic.Loc()),
 		Code: &lsproto.IntegerOrString{
@@ -68,6 +83,14 @@ func toLSPDiagnostic(diagnostic *ast.Diagnostic, converters *Converters) *lsprot
 		Severity:           &severity,
 		Message:            diagnostic.Message(),
 		Source:             ptrTo("ts"),
-		RelatedInformation: &relatedInformation,
+		RelatedInformation: ptrToSliceIfNonEmpty(relatedInformation),
+		Tags:               ptrToSliceIfNonEmpty(tags),
+	}
+}
+
+func ptrToSliceIfNonEmpty[T any](s []T) *[]T {
+	if len(s) == 0 {
+		return nil
 	}
+	return &s
 }