diff --git a/include/swift/AST/DiagnosticBridge.h b/include/swift/AST/DiagnosticBridge.h
index b110f530e9b6b..81a161aa3a549 100644
--- a/include/swift/AST/DiagnosticBridge.h
+++ b/include/swift/AST/DiagnosticBridge.h
@@ -46,6 +46,10 @@ class DiagnosticBridge {
   void enqueueDiagnostic(SourceManager &SM, const DiagnosticInfo &Info,
                          unsigned innermostBufferID);
 
+  /// Emit a single diagnostic without location information.
+  void emitDiagnosticWithoutLocation(
+      const DiagnosticInfo &Info, llvm::raw_ostream &out, bool forceColors);
+
   /// Flush all enqueued diagnostics.
   void flush(llvm::raw_ostream &OS, bool includeTrailingBreak,
              bool forceColors);
diff --git a/include/swift/Bridging/ASTGen.h b/include/swift/Bridging/ASTGen.h
index afef5603a99c7..b72b9a52d4814 100644
--- a/include/swift/Bridging/ASTGen.h
+++ b/include/swift/Bridging/ASTGen.h
@@ -35,6 +35,14 @@ void swift_ASTGen_addQueuedDiagnostic(
     const BridgedCharSourceRange *_Nullable highlightRanges,
     ptrdiff_t numHighlightRanges,
     BridgedArrayRef /*BridgedFixIt*/ fixIts);
+void swift_ASTGen_renderSingleDiagnostic(
+    void *_Nonnull state,
+    BridgedStringRef text,
+    BridgedDiagnosticSeverity severity,
+    BridgedStringRef categoryName,
+    BridgedStringRef documentationPath,
+    ssize_t colorize,
+    BridgedStringRef *_Nonnull renderedString);
 void swift_ASTGen_renderQueuedDiagnostics(
     void *_Nonnull queued, ssize_t contextSize, ssize_t colorize,
     BridgedStringRef *_Nonnull renderedString);
diff --git a/lib/AST/DiagnosticBridge.cpp b/lib/AST/DiagnosticBridge.cpp
index 859acbb22c2d6..e79cb386771ea 100644
--- a/lib/AST/DiagnosticBridge.cpp
+++ b/lib/AST/DiagnosticBridge.cpp
@@ -26,6 +26,22 @@
 using namespace swift;
 
 #if SWIFT_BUILD_SWIFT_SYNTAX
+static BridgedDiagnosticSeverity bridgeDiagnosticSeverity(DiagnosticKind kind) {
+  switch (kind) {
+  case DiagnosticKind::Error:
+    return BridgedDiagnosticSeverity::BridgedError;
+
+  case DiagnosticKind::Warning:
+    return BridgedDiagnosticSeverity::BridgedWarning;
+
+  case DiagnosticKind::Remark:
+    return BridgedDiagnosticSeverity::BridgedRemark;
+
+  case DiagnosticKind::Note:
+    return BridgedDiagnosticSeverity::BridgedNote;
+  }
+}
+
 /// Enqueue a diagnostic with ASTGen's diagnostic rendering.
 static void addQueueDiagnostic(void *queuedDiagnostics,
                                void *perFrontendState,
@@ -37,24 +53,7 @@ static void addQueueDiagnostic(void *queuedDiagnostics,
                                            info.FormatArgs);
   }
 
-  BridgedDiagnosticSeverity severity;
-  switch (info.Kind) {
-  case DiagnosticKind::Error:
-    severity = BridgedDiagnosticSeverity::BridgedError;
-    break;
-
-  case DiagnosticKind::Warning:
-    severity = BridgedDiagnosticSeverity::BridgedWarning;
-    break;
-
-  case DiagnosticKind::Remark:
-    severity = BridgedDiagnosticSeverity::BridgedRemark;
-    break;
-
-  case DiagnosticKind::Note:
-    severity = BridgedDiagnosticSeverity::BridgedNote;
-    break;
-  }
+  BridgedDiagnosticSeverity severity = bridgeDiagnosticSeverity(info.Kind);
 
   // Map the highlight ranges.
   SmallVector<BridgedCharSourceRange, 2> highlightRanges;
@@ -87,6 +86,39 @@ static void addQueueDiagnostic(void *queuedDiagnostics,
   }
 }
 
+void DiagnosticBridge::emitDiagnosticWithoutLocation(
+    const DiagnosticInfo &info, llvm::raw_ostream &out, bool forceColors) {
+  ASSERT(queuedDiagnostics == nullptr);
+
+  // If we didn't have per-frontend state before, create it now.
+  if (!perFrontendState) {
+    perFrontendState = swift_ASTGen_createPerFrontendDiagnosticState();
+  }
+
+  llvm::SmallString<256> text;
+  {
+    llvm::raw_svector_ostream out(text);
+    DiagnosticEngine::formatDiagnosticText(out, info.FormatString,
+                                           info.FormatArgs);
+  }
+
+  BridgedDiagnosticSeverity severity = bridgeDiagnosticSeverity(info.Kind);
+
+  BridgedStringRef bridgedRenderedString{nullptr, 0};
+  swift_ASTGen_renderSingleDiagnostic(
+      perFrontendState, text.str(), severity, info.Category,
+      llvm::StringRef(info.CategoryDocumentationURL), forceColors ? 1 : 0,
+      &bridgedRenderedString);
+
+  auto renderedString = bridgedRenderedString.unbridged();
+  if (renderedString.data()) {
+    out << "<unknown>:0: ";
+    out.write(renderedString.data(), renderedString.size());
+    swift_ASTGen_freeBridgedString(renderedString);
+    out << "\n";
+  }
+}
+
 void DiagnosticBridge::enqueueDiagnostic(SourceManager &SM,
                                          const DiagnosticInfo &Info,
                                          unsigned innermostBufferID) {
diff --git a/lib/ASTGen/Sources/ASTGen/DiagnosticsBridge.swift b/lib/ASTGen/Sources/ASTGen/DiagnosticsBridge.swift
index 6d733229c2e1a..5f0eab41ed26c 100644
--- a/lib/ASTGen/Sources/ASTGen/DiagnosticsBridge.swift
+++ b/lib/ASTGen/Sources/ASTGen/DiagnosticsBridge.swift
@@ -425,6 +425,60 @@ public func addQueuedDiagnostic(
   queuedDiagnostics.pointee.grouped.addDiagnostic(diagnostic)
 }
 
+/// Render a single diagnostic that has no source location information.
+@_cdecl("swift_ASTGen_renderSingleDiagnostic")
+public func renderSingleDiagnostic(
+  perFrontendDiagnosticStatePtr: UnsafeMutableRawPointer,
+  text: BridgedStringRef,
+  severity: BridgedDiagnosticSeverity,
+  categoryName: BridgedStringRef,
+  documentationPath: BridgedStringRef,
+  colorize: Int,
+  renderedStringOutPtr: UnsafeMutablePointer<BridgedStringRef>
+) {
+  let diagnosticState = perFrontendDiagnosticStatePtr.assumingMemoryBound(
+    to: PerFrontendDiagnosticState.self
+  )
+
+  let documentationPath = String(bridged: documentationPath)
+  let documentationURL: String? = if !documentationPath.isEmpty {
+      // If this looks doesn't look like a URL, prepend file://.
+      documentationPath.looksLikeURL ? documentationPath : "file://\(documentationPath)"
+    } else {
+      nil
+    }
+
+  let categoryName = String(bridged: categoryName)
+  // If the data comes from serialized diagnostics, it's possible that
+  // the category name is empty because StringRef() is serialized into
+  // an empty string.
+  let category: DiagnosticCategory? = if !categoryName.isEmpty {
+      DiagnosticCategory(
+        name: categoryName,
+        documentationURL: documentationURL
+      )
+    } else {
+      nil
+    }
+
+  // Note that we referenced this category.
+  if let category {
+    diagnosticState.pointee.referencedCategories.insert(category)
+  }
+
+  let formatter = DiagnosticsFormatter(colorize: colorize != 0)
+
+  let renderedStr = formatter.formattedMessage(
+    SimpleDiagnostic(
+      message: String(bridged: text),
+      severity: severity.asSeverity,
+      category: category
+    )
+  )
+
+  renderedStringOutPtr.pointee = allocateBridgedString(renderedStr)
+}
+
 /// Render the queued diagnostics into a UTF-8 string.
 @_cdecl("swift_ASTGen_renderQueuedDiagnostics")
 public func renderQueuedDiagnostics(
diff --git a/lib/Frontend/PrintingDiagnosticConsumer.cpp b/lib/Frontend/PrintingDiagnosticConsumer.cpp
index 00806723d8c34..79120207045e8 100644
--- a/lib/Frontend/PrintingDiagnosticConsumer.cpp
+++ b/lib/Frontend/PrintingDiagnosticConsumer.cpp
@@ -48,20 +48,20 @@ void PrintingDiagnosticConsumer::handleDiagnostic(SourceManager &SM,
 #if SWIFT_BUILD_SWIFT_SYNTAX
     // Use the swift-syntax formatter.
     auto bufferStack = DiagnosticBridge::getSourceBufferStack(SM, Info.Loc);
-    if (!bufferStack.empty()) {
-      if (Info.Kind != DiagnosticKind::Note)
-        DiagBridge.flush(Stream, /*includeTrailingBreak=*/true,
-                         /*forceColors=*/ForceColors);
+    if (Info.Kind != DiagnosticKind::Note || bufferStack.empty())
+      DiagBridge.flush(Stream, /*includeTrailingBreak=*/true,
+                       /*forceColors=*/ForceColors);
 
+    if (bufferStack.empty()) {
+      DiagBridge.emitDiagnosticWithoutLocation(Info, Stream, ForceColors);
+    } else {
       DiagBridge.enqueueDiagnostic(SM, Info, bufferStack.front());
-      break;
     }
-#endif
-
+    return;
+#else
     // Fall through when we don't have the new diagnostics renderer available.
-    // This also happens if the location of the diagnostic is invalid, because
-    // the new rendered cannot cope with that.
     LLVM_FALLTHROUGH;
+#endif
   }
 
   case DiagnosticOptions::FormattingStyle::LLVM:
@@ -215,4 +215,6 @@ PrintingDiagnosticConsumer::PrintingDiagnosticConsumer(
     llvm::raw_ostream &stream)
     : Stream(stream) {}
 
-PrintingDiagnosticConsumer::~PrintingDiagnosticConsumer() {}
+PrintingDiagnosticConsumer::~PrintingDiagnosticConsumer() {
+  flush();
+}