[cfe-commits] [PATCH] Allow typedef with unnecessary "typename" when ms-extensions are enabled.

[Nico Weber]

Out of interest, which headers do you need this for?

On Wed, May 2, 2012 at 6:54 AM, William Wilson <will at indefiant.com> wrote:

> Hi All,
>
> This patch follows on from http://llvm.org/bugs/show_bug.cgi?id=12715
> and includes a test case for validation. Local testing shows no
> regression.
>
> Original outline of issue from bug report:
>
> ----
>
> I've run into a issue parsing headers where the following constructs are
> (frequently) used and successfully compiled by the MSVC compilers:
>
> template <typename T>
> class Foo
> {
>  typedef typename T* pT;
> };
>
> The additional typename qualification is unnecessary and causes the
> following
> warning to be emitted from Parser::TryAnnotateTypeOrScopeToken():
>
> warning: expected a qualified name after 'typename'
>        typedef typename T* pT;
>
> Which is fine and expected, however the parsing quickly fails with:
>
> error: expected ';' at end of declaration list
>        typedef typename T* pT;
>
> This appears to be due the return true (error occurred) from
> TryAnnotateTypeOrScopeToken() even though the occurrence is treated as a
> warning.
>
> Interestingly the original commit that introduced the warning (r130088 by
> fpichet) states the following:
>
> "Must "return true;" even if it is a warning because the rest of the code
> path
> assumes that SS is set to something. The parser will get back on its feet
> and
> continue parsing the rest of the declaration correctly so it is not a
> problem."
>
> It's true that the rest of the code expects SS to be valid, but
> unfortunately
> the assumption that the "parser will get back on its feet" is not true
> with the
> current implementation.
>
> I tried a naive return false (no error) in the event of the
> diag::warn_expected_qualified_after_typename instance and the parser
> appeared
> to recover successfully, but being unfamiliar with the logic in question I
> wonder if that is the correct approach for recovery in this case?
>
> ----
>
> Other concerns:
>
> Do I need to annotate the typename token before the return false?
>
> Additionally, this recovery state seems more applicable to
> ms-compatibility rather than ms-extensions, but as r130088 uses
> MicrosoftExt I chose to leave it as is. Any thoughts?
>
> All the best,
> Will.
>
> PS. Many thanks for all the excellent work. It's probably the finest
> large-scale code base I've had the pleasure to work with.
>
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>
>
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