[Clang] Added comment and updated the clang release notes

Author: TilakChad

clang/docs/ReleaseNotes.rst

@@ -926,6 +926,7 @@ Bug Fixes to C++ Support
   (`LWG3929 <https://wg21.link/LWG3929>`__.) (#GH121278)
 - Clang now identifies unexpanded parameter packs within the type constraint on a non-type template parameter. (#GH88866)
 - Fixed an issue while resolving type of expression indexing into a pack of values of non-dependent type (#GH121242)
+- Fixed a crash when __PRETTY_FUNCTION__ or __FUNCSIG__ (clang-cl) appears in the trailing return type of the lambda (#GH121274)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/AST/Expr.cpp

@@ -775,6 +775,9 @@ std::string PredefinedExpr::ComputeName(PredefinedIdentKind IK,
     if (const FunctionDecl* Pattern = FD->getTemplateInstantiationPattern())
       Decl = Pattern;
 
+    // Bail out if the type of the function has not been set yet.
+    // This can notably happen in the trailing return type of a lambda
+    // expression.
     const Type *Ty = Decl->getType().getTypePtrOrNull();
     if (!Ty)
       return "";