Implement reportStyleChecksAsWarnings

internal/fourslash/fourslash.go

@@ -2568,8 +2568,7 @@ func (f *FourslashTest) getDiagnostics(t *testing.T, fileName string) []*lsproto
 }
 
 func isSuggestionDiagnostic(diag *lsproto.Diagnostic) bool {
-	return diag.Tags != nil && len(*diag.Tags) > 0 ||
-		(diag.Severity != nil && *diag.Severity == lsproto.DiagnosticSeverityHint)
+	return diag.Severity != nil && *diag.Severity == lsproto.DiagnosticSeverityHint
 }
 
 func (f *FourslashTest) VerifyBaselineNonSuggestionDiagnostics(t *testing.T) {

internal/fourslash/tests/unreachableCodeDiagnostics_test.go

@@ -0,0 +1,21 @@
+package fourslash_test
+
+import (
+	"testing"
+
+	"github.com/microsoft/typescript-go/internal/fourslash"
+	"github.com/microsoft/typescript-go/internal/testutil"
+)
+
+func TestUnreachableCodeDiagnostics(t *testing.T) {
+	t.Parallel()
+
+	defer testutil.RecoverAndFail(t, "Panic on fourslash test")
+	const content = `// @allowUnreachableCode: false
+throw new Error();
+
+(() => {})();
+	`
+	f := fourslash.NewFourslash(t, nil /*capabilities*/, content)
+	f.VerifyBaselineNonSuggestionDiagnostics(t)
+}

internal/ls/diagnostics.go

@@ -16,7 +16,6 @@ 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))
@@ -37,7 +36,7 @@ func (l *LanguageService) toLSPDiagnostics(ctx context.Context, diagnostics ...[
 	lspDiagnostics := make([]*lsproto.Diagnostic, 0, size)
 	for _, diagSlice := range diagnostics {
 		for _, diag := range diagSlice {
-			lspDiagnostics = append(lspDiagnostics, lsconv.DiagnosticToLSPPull(ctx, l.converters, diag))
+			lspDiagnostics = append(lspDiagnostics, lsconv.DiagnosticToLSPPull(ctx, l.converters, diag, l.UserPreferences().ReportStyleChecksAsWarnings))
 		}
 	}
 	return lspDiagnostics

internal/ls/lsconv/converters.go

@@ -10,6 +10,7 @@ import (
 	"unicode/utf8"
 
 	"github.com/microsoft/typescript-go/internal/ast"
+	"github.com/microsoft/typescript-go/internal/collections"
 	"github.com/microsoft/typescript-go/internal/core"
 	"github.com/microsoft/typescript-go/internal/diagnostics"
 	"github.com/microsoft/typescript-go/internal/diagnosticwriter"
@@ -204,30 +205,44 @@ func ptrTo[T any](v T) *T {
 	return &v
 }
 
-type diagnosticCapabilities struct {
-	relatedInformation bool
-	tagValueSet        []lsproto.DiagnosticTag
+type diagnosticOptions struct {
+	reportStyleChecksAsWarnings bool
+	relatedInformation          bool
+	tagValueSet                 []lsproto.DiagnosticTag
 }
 
 // DiagnosticToLSPPull converts a diagnostic for pull diagnostics (textDocument/diagnostic)
-func DiagnosticToLSPPull(ctx context.Context, converters *Converters, diagnostic *ast.Diagnostic) *lsproto.Diagnostic {
+func DiagnosticToLSPPull(ctx context.Context, converters *Converters, diagnostic *ast.Diagnostic, reportStyleChecksAsWarnings bool) *lsproto.Diagnostic {
 	clientCaps := lsproto.GetClientCapabilities(ctx).TextDocument.Diagnostic
-	return diagnosticToLSP(converters, diagnostic, diagnosticCapabilities{
-		relatedInformation: clientCaps.RelatedInformation,
-		tagValueSet:        clientCaps.TagSupport.ValueSet,
+	return diagnosticToLSP(converters, diagnostic, diagnosticOptions{
+		reportStyleChecksAsWarnings: reportStyleChecksAsWarnings, // !!! get through context UserPreferences
+		relatedInformation:          clientCaps.RelatedInformation,
+		tagValueSet:                 clientCaps.TagSupport.ValueSet,
 	})
 }
 
 // DiagnosticToLSPPush converts a diagnostic for push diagnostics (textDocument/publishDiagnostics)
 func DiagnosticToLSPPush(ctx context.Context, converters *Converters, diagnostic *ast.Diagnostic) *lsproto.Diagnostic {
 	clientCaps := lsproto.GetClientCapabilities(ctx).TextDocument.PublishDiagnostics
-	return diagnosticToLSP(converters, diagnostic, diagnosticCapabilities{
+	return diagnosticToLSP(converters, diagnostic, diagnosticOptions{
 		relatedInformation: clientCaps.RelatedInformation,
 		tagValueSet:        clientCaps.TagSupport.ValueSet,
 	})
 }
 
-func diagnosticToLSP(converters *Converters, diagnostic *ast.Diagnostic, caps diagnosticCapabilities) *lsproto.Diagnostic {
+// https://github.com/microsoft/vscode/blob/93e08afe0469712706ca4e268f778cfadf1a43ef/extensions/typescript-language-features/src/typeScriptServiceClientHost.ts#L40C7-L40C29
+var styleCheckDiagnostics = collections.NewSetFromItems(
+	diagnostics.X_0_is_declared_but_never_used.Code(),
+	diagnostics.X_0_is_declared_but_its_value_is_never_read.Code(),
+	diagnostics.Property_0_is_declared_but_its_value_is_never_read.Code(),
+	diagnostics.All_imports_in_import_declaration_are_unused.Code(),
+	diagnostics.Unreachable_code_detected.Code(),
+	diagnostics.Unused_label.Code(),
+	diagnostics.Fallthrough_case_in_switch.Code(),
+	diagnostics.Not_all_code_paths_return_a_value.Code(),
+)
+
+func diagnosticToLSP(converters *Converters, diagnostic *ast.Diagnostic, opts diagnosticOptions) *lsproto.Diagnostic {
 	var severity lsproto.DiagnosticSeverity
 	switch diagnostic.Category() {
 	case diagnostics.CategorySuggestion:
@@ -240,8 +255,12 @@ func diagnosticToLSP(converters *Converters, diagnostic *ast.Diagnostic, caps di
 		severity = lsproto.DiagnosticSeverityError
 	}
 
+	if opts.reportStyleChecksAsWarnings && severity == lsproto.DiagnosticSeverityError && styleCheckDiagnostics.Has(diagnostic.Code()) {
+		severity = lsproto.DiagnosticSeverityWarning
+	}
+
 	var relatedInformation []*lsproto.DiagnosticRelatedInformation
-	if caps.relatedInformation {
+	if opts.relatedInformation {
 		relatedInformation = make([]*lsproto.DiagnosticRelatedInformation, 0, len(diagnostic.RelatedInformation()))
 		for _, related := range diagnostic.RelatedInformation() {
 			relatedInformation = append(relatedInformation, &lsproto.DiagnosticRelatedInformation{
@@ -255,12 +274,12 @@ func diagnosticToLSP(converters *Converters, diagnostic *ast.Diagnostic, caps di
 	}
 
 	var tags []lsproto.DiagnosticTag
-	if len(caps.tagValueSet) > 0 && (diagnostic.ReportsUnnecessary() || diagnostic.ReportsDeprecated()) {
+	if len(opts.tagValueSet) > 0 && (diagnostic.ReportsUnnecessary() || diagnostic.ReportsDeprecated()) {
 		tags = make([]lsproto.DiagnosticTag, 0, 2)
-		if diagnostic.ReportsUnnecessary() && slices.Contains(caps.tagValueSet, lsproto.DiagnosticTagUnnecessary) {
+		if diagnostic.ReportsUnnecessary() && slices.Contains(opts.tagValueSet, lsproto.DiagnosticTagUnnecessary) {
 			tags = append(tags, lsproto.DiagnosticTagUnnecessary)
 		}
-		if diagnostic.ReportsDeprecated() && slices.Contains(caps.tagValueSet, lsproto.DiagnosticTagDeprecated) {
+		if diagnostic.ReportsDeprecated() && slices.Contains(opts.tagValueSet, lsproto.DiagnosticTagDeprecated) {
 			tags = append(tags, lsproto.DiagnosticTagDeprecated)
 		}
 	}

internal/ls/lsutil/userpreferences.go

@@ -19,6 +19,7 @@ func NewDefaultUserPreferences() *UserPreferences {
 		IncludeCompletionsWithSnippetText:  core.TSTrue,
 		DisplayPartsForJSDoc:               true,
 		DisableLineTextInReferences:        true,
+		ReportStyleChecksAsWarnings:        true,
 	}
 }
 
@@ -148,6 +149,7 @@ type UserPreferences struct {
 	DisableSuggestions           bool // !!!
 	DisableLineTextInReferences  bool // !!!
 	DisplayPartsForJSDoc         bool // !!!
+	ReportStyleChecksAsWarnings  bool // !!! If this changes, we need to ask the client to recompute diagnostics
 }
 
 type JsxAttributeCompletionStyle string
@@ -628,5 +630,7 @@ func (p *UserPreferences) set(name string, value any) {
 		p.DisableLineTextInReferences = parseBoolWithDefault(value, true)
 	case "displaypartsforjsdoc":
 		p.DisplayPartsForJSDoc = parseBoolWithDefault(value, true)
+	case "reportstylechecksaswarnings":
+		p.ReportStyleChecksAsWarnings = parseBoolWithDefault(value, true)
 	}
 }

testdata/baselines/reference/fourslash/syntaxandSemanticDiagnostics/unreachableCodeDiagnostics.baseline

@@ -0,0 +1,11 @@
+// === Syntax and Semantic Diagnostics ===
+/unreachableCodeDiagnostics.ts(3,1): warning TS7027: Unreachable code detected.
+
+
+==== /unreachableCodeDiagnostics.ts (1 errors) ====
+    throw new Error();
+
+    (() => {})();
+    ~~~~~~~~~~~~~
+!!! warning TS7027: Unreachable code detected.
+