Douglas Gregor | 19 Nov 20:48 2011

Re: [PATCH] Sema and AST for C++0x Lambda Expressions

On Nov 15, 2011, at 10:45 PM, John Freeman wrote:

> I finished integrating your LambdaScopeInfo changes with my work since my last patch submission.
Divergent branches aren't fun. :/

No, they aren't. Sorry for going rogue :)

> I saw you switched from using CheckFieldDecl to directly using FieldDecl::Create. Was that
intentional? I had the impression that the extra semantic checking was preferred. Same question about
switching from ActOnIdExpression to directly using name lookup.

We don't need most of the checking in CheckFieldDecl, since a proper AST already maintains most of those
invariants. Plus, all of the field-centric diagnostics would be wrong.

Similarly with ActOnIdExpression; I'd much rather that we just did unqualified name lookup and inspect
the result appropriately.

> A few problems concerning the CXXMethodDecl (henceforth called Method):
> A. I was trying to use ActOnStartOfFunctionDef to enter the DeclContext owned by Method. You had used
PushDeclContext directly. I believe that will be necessary to avoid creating an extraneous
FunctionScopeInfo, but do we want any of the extra checking in ActOnStartOfFunctionDef?

The necessary checking should be factored out of ActOnStartOfFunctionDef so that both routines can use it
(separate patches).

> B. A conundrum:
> - PushDeclContext requires that the lexical DeclContext for Method be CurContext.
> - CXXRecordDecl::addDecl requires that the lexical DeclContext for Method be the CXXRecordDecl
(henceforth called Class).
> How about this solution? :
> 1. Method.setLexicalDeclContext(CurContext).
> 2. PushDeclContext.
> 3. Add Method to the LambdaScopeInfo so that it can be retrieved later (we can't look it up in Class because
we haven't called addDecl yet).
> 4. Parse body.
> 5. Retrieve Method from the LambdaScopeInfo.
> 6. ActOnFinishFunctionBody (calls PopDeclContext).
> 7. Method.setLexicalDeclContext(Class).
> 8. Class.addDecl(Method).

This seems okay, but why not just perform the addDecl early on, and push both the Class context and the Method
context? (in other words, handle this like an inline member function of a local class)

> C. In a similar question to part A on ActOnStartOfFunctionDef vs PushDeclContext, concerning step 6
above, do we want to use PopDeclContext directly instead of ActOnFinishFunctionBody, or do we want the
extra semantic checks?

Again, I think the answer is to refactor. Blocks have some end-of-body checking; that's very much in the
same realm.

This is very much a refactor-and-then-implement sort of feature, if I haven't made that obvious :)

	- Doug