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: > 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! 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