Fix diagnostic error due to auto type during copy initialization/impl…

…icit cast

clang/lib/Sema/SemaOverload.cpp

@@ -2608,6 +2608,19 @@ bool Sema::IsPointerConversion(Expr *From, QualType FromType, QualType ToType,
     return true;
   }
 
+  // Note(kumarak): If the auto pointee type leaks into the implict cast, check
+  //                if FromPointeeType is undeduced and generate converted type
+  //                based on ToType. The patch avoids Diagnostic error due to
+  //                invalid cast from auto to another type.
+  if (getLangOpts().LexicalTemplateInstantiation) {
+    if (FromPointeeType->isUndeducedAutoType()) {
+      ConvertedType = BuildSimilarlyQualifiedPointerType(FromTypePtr,
+                                                       ToPointeeType,
+                                                      ToType, Context);
+      return true;
+    }
+  }
+
   return false;
 }
 

clang/lib/Sema/SemaStmt.cpp

@@ -4160,7 +4160,15 @@ StmtResult Sema::BuildReturnStmt(SourceLocation ReturnLoc, Expr *RetValExp,
 
     // In C++ the return statement is handled via a copy initialization,
     // the C version of which boils down to CheckSingleAssignmentConstraints.
-    if (!HasDependentReturnType && !RetValExp->isTypeDependent()) {
+
+    // Note(kumarak): If the Return value expression has undeduced auto types,
+    //                don't perform the copy operation instead force cast it
+    //                as unknown any types. Peforming copy operation on
+    //                from undeduced expression will cause diagnostic error.
+
+    auto HasUndeducedAutoType = getLangOpts().LexicalTemplateInstantiation &&
+                                      RetValExp->getType()->isUndeducedAutoType();
+    if (!HasDependentReturnType && !RetValExp->isTypeDependent() && !HasUndeducedAutoType) {
       // we have a non-void function with an expression, continue checking
       InitializedEntity Entity =
           InitializedEntity::InitializeResult(ReturnLoc, RetType);