mizvekov added inline comments.
================
Comment at: clang/lib/Sema/SemaTemplateDeduction.cpp:5455-5456
if (!ClangABICompat15) {
- // Consider this a fix for CWG1432. Similar to the fix for CWG1395.
auto *TST1 = T1->castAs<TemplateSpecializationType>();
auto *TST2 = T2->castAs<TemplateSpecializationType>();
+ const TemplateArgument &TA1 = TST1->template_arguments().back();
----------------
ychen wrote:
> mizvekov wrote:
> > ychen wrote:
> > > ychen wrote:
> > > > mizvekov wrote:
> > > > > This is a bug, T1 and T2 are not in general canonical types for this
> > > > > function, and this castAs can pick up an alias template, and these
> > > > > should never participate in deduction.
> > > > >
> > > > > (Also, can you please add a test for that?)
> > > > >
> > > > > You should not need to keep sugar here, everything being tested below
> > > > > is present on the canonical type, so this is simple to solve, as
> > > > > suggested.
> > > > I see. I'll add a test.
> > > Looking more closely, `T1`/`T2` is mostly returned by
> > > `ASTContext::getTemplateSpecializationType` and for injected template
> > > specialization, always unqualified
> > > https://github.com/llvm/llvm-project/blob/52dce8900c46d5842a021619537ede598983dfde/clang/include/clang/AST/Type.h#L5431-L5432
> > > , it does not seem possible to have aliase template involved? I could've
> > > missed something though.
> > Yeah you are right, I missed that all the uses of this function, those
> > types either come from an Injected TST, or a dependent TST created on the
> > spot.
> >
> > But yeah, the change to a simple `cast` instead of `castAs` makes this more
> > clear.
> >
> > Otherwise, if there could have been any sugar node on top of the TST, that
> > sugar could have easily been an alias TST,
> > and I think it's very unlikely one wouldn't care, as they are very
> > different things.
> >
> > So I tend to view these as potential bugs, a simple `getAs` and `castAs` on
> > TSTs, which does not check or keeps digging through alias templates is
> > highly suspicious :)
> >
> > Thanks for taking a look at this though!
> Thanks for the explanation. Yeah, `castAs` looks misleading indeed. I wasn't
> aware of the subtle difference between `cast` and `castAs`. BTW, are you
> comfortable accepting this patch?
I hope I answered that in my other comment, but since this is a speculative
wording fix, I think it's more reasonable to wait more than a week for other
reviewers, specially since folks can be on time off and such.
But lacking interest from other folks in reviewing this, yeah sure.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D133683/new/
https://reviews.llvm.org/D133683
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
