aaron.ballman added inline comments.

================
Comment at: clang/lib/Sema/Sema.cpp:460-462
+        Scope S(TUScope, Scope::DeclScope, getDiagnostics());
+        PushDeclContext(&S, DC);
+        PushOnScopeChains(ND, &S);
----------------
erichkeane wrote:
> mizvekov wrote:
> > aaron.ballman wrote:
> > > Is it valid to use a local variable as a `Scope` object? I would assume 
> > > that scope goes away at the end of this compound statement? I didn't spot 
> > > other cases where we did this -- usually we call `Parser::EnterScope()` 
> > > which allocates a new `Scope` that `Sema` then uses.
> > I don't see anything problematic about allocating it on the stack like 
> > this, implementation-wise.
> > 
> > I thought it would be a bit counter-intuitive to use parser functions here, 
> > since these declarations are entirely synthetic.
> I dont know much about "Scope", as it is particularly used in Parsing, but I 
> DO see the comment says: "A scope is a transient data structure that is used 
> while parsing the program.  It assists with resolving identifiers to the 
> appropriate declaration."
> 
> Which means to me it doesn't need to out-live its parsing time.  I THINK it 
> gets replaced with a CXXScope at one point, but I dont know when/where that 
> happens.
> 
The situation I'm worried about (and maybe it's not a valid concern) is that 
`Parser::EnterScope` uses a cache of scopes that this bypasses and I'm not 
certain whether that's a good thing or not. I *think* it might be reasonable 
(`Scope` is just a holder for a `DeclContext` and that's the object which has 
all the declarations added to and removed from, and that context outlives the 
`Scope` object), but it's worth double-checking.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D136886/new/

https://reviews.llvm.org/D136886

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