[clang] [Serialization] Check for stack exhaustion when reading declarations (PR #79875)

[David Blaikie via cfe-commits]

dwblaikie wrote:

> > Could you show the stack (omitting/annotating the repeated part) that leads to failure? and/or the AST shape that leads to failure?
> 
> See the test I added. All you need is ~10k overloads of a method in a class and a `using Base::func` in the derived class. The AST represents that as a linked list inside `UsingShadowDecl` (each shadow decl references the next one). Serializing them works fine, but deserialization is recursive and blows up.
> 
> Feel free to just call `-ast-dump` on the test I posted (it only crashes when reading the pcm, so outputing AST should be fine)

Yeah, I was hoping to have it in the text of the discussion here without having to do it myself since you've already got the repro locally, presumably... so we can all see/discuss it. But perhaps it's not sufficiently helpful/constructive to worry about - not sure.

https://github.com/llvm/llvm-project/pull/79875