[Diagnostics] Let the swift-syntax formatter handle multiple files itself

Author: DougGregor

include/swift/Frontend/PrintingDiagnosticConsumer.h

@@ -50,7 +50,6 @@ class PrintingDiagnosticConsumer : public DiagnosticConsumer {
   /// The queued diagnostics structure.
   void *queuedDiagnostics = nullptr;
   llvm::DenseMap<unsigned, QueuedBuffer> queuedBuffers;
-  unsigned queuedDiagnosticsOutermostBufferID;
 
 public:
   PrintingDiagnosticConsumer(llvm::raw_ostream &stream = llvm::errs());

lib/Frontend/PrintingDiagnosticConsumer.cpp

@@ -458,16 +458,10 @@ void PrintingDiagnosticConsumer::handleDiagnostic(SourceManager &SM,
     // Use the swift-syntax formatter.
     auto bufferStack = getSourceBufferStack(SM, Info.Loc);
     if (!bufferStack.empty()) {
-      // If there are no enqueued diagnostics, they are from a different
-      // outermost buffer, or we have hit a non-note diagnostic, flush any
-      // enqueued diagnostics and start fresh.
-      unsigned outermostBufferID = bufferStack.back();
-      if (!queuedDiagnostics ||
-          outermostBufferID != queuedDiagnosticsOutermostBufferID ||
-          Info.Kind != DiagnosticKind::Note) {
+      // If there are no enqueued diagnostics, or we have hit a non-note
+	// diagnostic, flush any enqueued diagnostics and start fresh.
+      if (!queuedDiagnostics || Info.Kind != DiagnosticKind::Note) {
         flush(/*includeTrailingBreak*/ true);
-
-        queuedDiagnosticsOutermostBufferID = outermostBufferID;
         queuedDiagnostics = swift_ASTGen_createQueuedDiagnostics();
       }