[clang] Reduce memory usage in AST parent map generation by lazily checking if nodes have been seen (PR #129934)

[Erich Keane via cfe-commits]

erichkeane wrote:

> > One is that I noticed `ASTContext::getTraversalScope()` is returning a vector by copy and that doesn't seem necessary. 

I noticed this too!  I'm actually working on validating a RAC fix for this right now, just to have it return an ArrayRef instead.  Both uses of that function just do observation, so it seems reasonable enough

https://github.com/llvm/llvm-project/pull/129934