[cfe-dev] Modify (and reparse) AST

[Reid Kleckner]

Considering that MSVC rejects typename in places where it is required by
the standard, I don't think issuing fixits is appropriate if we assume that
users still want to build with MSVC.

It's way too late to go back and reparse with a new typename token by the
time we reach instantiation.  We've already done the first parse of the
template, and now we're transforming AST nodes.

I think we can probably add a hack for sizeof if we observe during
instantiation that the sizeof expr is really operating on a DeclRefExpr
that names a type and not a decl.  Then we have to turn that DeclRefExpr
into TypeSourceInfo, and I think we can rebuild a sizeof() expr that thinks
it got a type.  I'm not sure how to take apart a DeclRefExpr and go looking
for types with that name.



On Thu, Feb 13, 2014 at 12:49 PM, JB Feldman <jb.feldman at kyrus-tech.com>wrote:

> Is there a way to "modify the source" and reparse the text during the AST
> TreeTransform process?
>
> I am trying to make a local change that would fix the bug:
> http://llvm.org/bugs/show_bug.cgi?id=18443
>
> The idea would be to replace the nodes that are rendered as:
> UnaryExprOrTypeTraitExpr 0x10c4f18 <col:41, col:55> 'unsigned int' sizeof
> `-ParenExpr 0x10c4f00 <col:47, col:55> '<dependent type>' lvalue
>   `-DependentScopeDeclRefExpr 0x10c4ed8 <col:48, col:51> '<dependent
> type>' lvalue
> with
> UnaryExprOrTypeTraitExpr 0xf64f28 <col:41, col:64> 'unsigned int' sizeof
> 'typename T::type'
>
> simply by adding "typename" before the symbol, and then the parser would
> handle it correctly. and generate the correct UnaryExprOrTypeTraitExpr
>
> Solutions I would accept include:
> 1) Change the source and reprocess the file (a la "Fixit"), but this has a
> high overhead for large files/projects
> 2) Ask the parser for the single Expr that would be generated from the new
> text
> 3) A way to look up what the existing typename would be manually and
> create the expr manually.
> 4) Other thing I'm too new to know about.
>
> Thanks,
> JB
>
> FYI: I'm trying to do this from the context of
> TransformUnaryExprOrTypeTraitExpr
>
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