Fix the const overload of IgnoreExprNodes

[d]

Summary

The existing code causes an infinite recursion. This is likely an
oversight of commit c0e5e3fbfa504c37 [1] where the intent must have been
to call the non-const overload.

[1] https://reviews.llvm.org/D87278

[d]

rebase

[gribozavr2]

Thanks for the fix! Do you have commit access?

[d]

In D100347#2684934, @gribozavr2 wrote:

Thanks for the fix! Do you have commit access?

Trying arc land I realize I do not...

[d]

@gribozavr2 it's also unclear to me where the tests for this are so I couldn't add a new test, is that OK?

[d]

More importantly, the bug exists in LLVM 12, what is the policy of patching the back branches in this project?

[gribozavr2]

Trying arc land I realize I do not...

Pushed as 595c3758e47042c876e7390d09642ea050ba6dbf.

it's also unclear to me where the tests for this are so I couldn't add a new test, is that OK?

Yes, unfortunately we don't have unit tests for the AST.

More importantly, the bug exists in LLVM 12, what is the policy of patching the back branches in this project?

Please take a look at https://llvm.org/docs/HowToReleaseLLVM.html#merge-requests .

clang/include/clang/AST/IgnoreExpr.h

 //===--- IgnoreExpr.h - Ignore intermediate Expressions -----------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 //
while (E != LastE) {
     LastE = E;
     E = detail::IgnoreExprNodesImpl(E, std::forward<FnTys>(Fns)...);
   }
   return E;
 }
 
 template <typename... FnTys>
 const Expr *IgnoreExprNodes(const Expr *E, FnTys &&...Fns) {
-  return const_cast<Expr *>(IgnoreExprNodes(E, std::forward<FnTys>(Fns)...));
+  return IgnoreExprNodes(const_cast<Expr *>(E), std::forward<FnTys>(Fns)...);
 }
 
 inline Expr *IgnoreImplicitCastsSingleStep(Expr *E) {
   if (auto *ICE = dyn_cast<ImplicitCastExpr>(E))
     return ICE->getSubExpr();
 
   if (auto *FE = dyn_cast<FullExpr>(E))
     return FE->getSubExpr();