[all-commits] [llvm/llvm-project] 7a7950: [clang] disallow narrowing when matching template ...

[Matheus Izvekov via All-commits]

  Branch: refs/heads/users/mizvekov/clang-cwg2398-nttp-narrowing
  Home:   https://github.com/llvm/llvm-project
  Commit: 7a7950dd8fd6a01cdc0d1351b86962798d300ea6
      https://github.com/llvm/llvm-project/commit/7a7950dd8fd6a01cdc0d1351b86962798d300ea6
  Author: Matheus Izvekov <mizvekov at gmail.com>
  Date:   2025-01-24 (Fri, 24 Jan 2025)

  Changed paths:
    M clang/docs/ReleaseNotes.rst
    M clang/include/clang/Basic/DiagnosticSemaKinds.td
    M clang/include/clang/Sema/Sema.h
    M clang/lib/Sema/SemaLookup.cpp
    M clang/lib/Sema/SemaOverload.cpp
    M clang/lib/Sema/SemaTemplate.cpp
    M clang/lib/Sema/SemaTemplateDeduction.cpp
    M clang/lib/Sema/SemaTemplateInstantiate.cpp
    M clang/test/CXX/drs/cwg0xx.cpp
    M clang/test/CXX/drs/cwg12xx.cpp
    M clang/test/CXX/drs/cwg3xx.cpp
    M clang/test/CXX/expr/expr.const/p3-0x.cpp
    M clang/test/CXX/temp/temp.arg/temp.arg.nontype/p1.cpp
    M clang/test/CXX/temp/temp.arg/temp.arg.template/p3-0x.cpp
    M clang/test/Modules/cxx-templates.cpp
    M clang/test/SemaObjCXX/noescape.mm
    M clang/test/SemaTemplate/cwg2398.cpp
    M clang/test/SemaTemplate/default-arguments.cpp
    M clang/test/SemaTemplate/instantiate-template-template-parm.cpp
    M clang/test/SemaTemplate/instantiation-default-2.cpp
    M clang/test/SemaTemplate/nested-template.cpp
    M clang/test/SemaTemplate/temp_arg_nontype_cxx1z.cpp
    M clang/test/SemaTemplate/temp_arg_nontype_cxx20.cpp
    M clang/test/SemaTemplate/temp_arg_template.cpp
    M clang/test/SemaTemplate/temp_arg_template_p0522.cpp

  Log Message:
  -----------
  [clang] disallow narrowing when matching template template parameters

This fixes the core issue described in P3579, following the design
intent of P0522 to not introduce any new cases where a template
template parameter match is allowed for a template which is not valid
for all possible uses.

With this patch, narrowing conversions is disallowed for TTP matching.

This reuses the existing machinery for diagnosing narrowing in
a converted constant expression.
Since P0522 is a DR and we apply it all the way back to C++98,
this brings that machinery to use in older standards, in this
very narrow scope of TTP matching.

This still doesn't solve the ambiguity when partial ordering NTTPs of
different integral types, this is blocked by a different bug which will
be fixed in a subsequent patch.



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