Index: clang/lib/Format/TokenAnnotator.cpp
===================================================================
--- clang/lib/Format/TokenAnnotator.cpp
+++ clang/lib/Format/TokenAnnotator.cpp
@@ -3310,6 +3310,11 @@
     }
   }
 
+  // trailing return type 'auto': []() -> auto {}, auto foo() -> auto {}
+  if (Left.is(tok::kw_auto) &&
+      Right.isOneOf(TT_LambdaLBrace, TT_FunctionLBrace))
+    return true;
+
   // auto{x} auto(x)
   if (Left.is(tok::kw_auto) && Right.isOneOf(tok::l_paren, tok::l_brace))
     return false;
Index: clang/unittests/Format/FormatTest.cpp
===================================================================
--- clang/unittests/Format/FormatTest.cpp
+++ clang/unittests/Format/FormatTest.cpp
@@ -23550,6 +23550,12 @@
   verifyFormat("auto lambda = [&a = a]() { a = 2; };", AlignStyle);
 }
 
+TEST_F(FormatTest, TrailingReturnTypeAuto) {
+  FormatStyle Style = getLLVMStyle();
+  verifyFormat("[]() -> auto { return Val; }", Style);
+  verifyFormat("auto foo() -> auto { return Val; }", Style);
+}
+
 TEST_F(FormatTest, SpacesInConditionalStatement) {
   FormatStyle Spaces = getLLVMStyle();
   Spaces.IfMacros.clear();