Fix data race in includeProcessor

Added mutex protection to includeProcessor to prevent concurrent access to processingDiagnostics and fileIncludeReasons. The data race was occurring when multiple goroutines in parseTask.load() called addProcessingDiagnostic simultaneously.

Changes:
- Added mu sync.Mutex to includeProcessor struct
- Protected all reads/writes to processingDiagnostics with mutex
- Protected all reads/writes to fileIncludeReasons with mutex
- Added addFileIncludeReason() and getFileIncludeReasons() helper methods
- Updated all direct field accesses to use protected methods
- Used maps.Copy in GetIncludeReasons() as suggested by linter

Co-authored-by: jakebailey <[email protected]>

Author: Copilot

internal/compiler/filesparser.go

@@ -427,10 +427,6 @@ func (w *filesParser) addIncludeReason(loader *fileLoader, task *parseTask, reas
 	if task.redirectedParseTask != nil {
 		w.addIncludeReason(loader, task.redirectedParseTask, reason)
 	} else if task.loaded {
-		if existing, ok := loader.includeProcessor.fileIncludeReasons[task.path]; ok {
-			loader.includeProcessor.fileIncludeReasons[task.path] = append(existing, reason)
-		} else {
-			loader.includeProcessor.fileIncludeReasons[task.path] = []*FileIncludeReason{reason}
-		}
+		loader.includeProcessor.addFileIncludeReason(task.path, reason)
 	}
 }

internal/compiler/includeprocessor.go

@@ -15,6 +15,7 @@ import (
 type includeProcessor struct {
 	fileIncludeReasons    map[tspath.Path][]*FileIncludeReason
 	processingDiagnostics []*processingDiagnostic
+	mu                    sync.Mutex // protects fileIncludeReasons and processingDiagnostics
 
 	reasonToReferenceLocation  collections.SyncMap[*FileIncludeReason, *referenceFileLocation]
 	includeReasonToRelatedInfo collections.SyncMap[*FileIncludeReason, *ast.Diagnostic]
@@ -35,7 +36,13 @@ func updateFileIncludeProcessor(p *Program) {
 func (i *includeProcessor) getDiagnostics(p *Program) *ast.DiagnosticsCollection {
 	i.computedDiagnosticsOnce.Do(func() {
 		i.computedDiagnostics = &ast.DiagnosticsCollection{}
-		for _, d := range i.processingDiagnostics {
+
+		i.mu.Lock()
+		diagnostics := make([]*processingDiagnostic, len(i.processingDiagnostics))
+		copy(diagnostics, i.processingDiagnostics)
+		i.mu.Unlock()
+
+		for _, d := range diagnostics {
 			i.computedDiagnostics.Add(d.toDiagnostic(p))
 		}
 		for _, resolutions := range p.resolvedModules {
@@ -57,14 +64,31 @@ func (i *includeProcessor) getDiagnostics(p *Program) *ast.DiagnosticsCollection
 }
 
 func (i *includeProcessor) addProcessingDiagnostic(d ...*processingDiagnostic) {
+	i.mu.Lock()
+	defer i.mu.Unlock()
 	i.processingDiagnostics = append(i.processingDiagnostics, d...)
 }
 
+func (i *includeProcessor) addFileIncludeReason(path tspath.Path, reason *FileIncludeReason) {
+	i.mu.Lock()
+	defer i.mu.Unlock()
+	i.fileIncludeReasons[path] = append(i.fileIncludeReasons[path], reason)
+}
+
+func (i *includeProcessor) getFileIncludeReasons(path tspath.Path) []*FileIncludeReason {
+	i.mu.Lock()
+	defer i.mu.Unlock()
+	return i.fileIncludeReasons[path]
+}
+
 func (i *includeProcessor) addProcessingDiagnosticsForFileCasing(file tspath.Path, existingCasing string, currentCasing string, reason *FileIncludeReason) {
+	i.mu.Lock()
+	defer i.mu.Unlock()
+
 	if !reason.isReferencedFile() && slices.ContainsFunc(i.fileIncludeReasons[file], func(r *FileIncludeReason) bool {
 		return r.isReferencedFile()
 	}) {
-		i.addProcessingDiagnostic(&processingDiagnostic{
+		i.processingDiagnostics = append(i.processingDiagnostics, &processingDiagnostic{
 			kind: processingDiagnosticKindExplainingFileInclude,
 			data: &includeExplainingDiagnostic{
 				file:             file,
@@ -74,7 +98,7 @@ func (i *includeProcessor) addProcessingDiagnosticsForFileCasing(file tspath.Pat
 			},
 		})
 	} else {
-		i.addProcessingDiagnostic(&processingDiagnostic{
+		i.processingDiagnostics = append(i.processingDiagnostics, &processingDiagnostic{
 			kind: processingDiagnosticKindExplainingFileInclude,
 			data: &includeExplainingDiagnostic{
 				file:             file,

internal/compiler/processingDiagnostic.go

@@ -97,7 +97,7 @@ func (d *processingDiagnostic) createDiagnosticExplainingFile(program *Program)
 	// !!! todo sheetal caching
 
 	if diag.file != "" {
-		reasons := program.includeProcessor.fileIncludeReasons[diag.file]
+		reasons := program.includeProcessor.getFileIncludeReasons(diag.file)
 		includeDetails = make([]*ast.Diagnostic, 0, len(reasons))
 		for _, reason := range reasons {
 			processInclude(reason)

internal/compiler/program.go

@@ -1562,7 +1562,12 @@ func (p *Program) GetSourceFiles() []*ast.SourceFile {
 
 // Testing only
 func (p *Program) GetIncludeReasons() map[tspath.Path][]*FileIncludeReason {
-	return p.includeProcessor.fileIncludeReasons
+	p.includeProcessor.mu.Lock()
+	defer p.includeProcessor.mu.Unlock()
+	// Return a copy to avoid concurrent access issues
+	result := make(map[tspath.Path][]*FileIncludeReason, len(p.includeProcessor.fileIncludeReasons))
+	maps.Copy(result, p.includeProcessor.fileIncludeReasons)
+	return result
 }
 
 // Testing only
@@ -1578,7 +1583,7 @@ func (p *Program) ExplainFiles(w io.Writer, locale locale.Locale) {
 	}
 	for _, file := range p.GetSourceFiles() {
 		fmt.Fprintln(w, toRelativeFileName(file.FileName()))
-		for _, reason := range p.includeProcessor.fileIncludeReasons[file.Path()] {
+		for _, reason := range p.includeProcessor.getFileIncludeReasons(file.Path()) {
 			fmt.Fprintln(w, "  ", reason.toDiagnostic(p, true).Localize(locale))
 		}
 		for _, diag := range p.includeProcessor.explainRedirectAndImpliedFormat(p, file, toRelativeFileName) {